THE MONTANA

STATE BOARD

OF

ENTOMOLOGY

SEVENTH BIENNIAL
REPORT

1927-1928

''■ ^^3,

THE MONTANA

STATE BOARD

OF

ENTOMOLOGY

SEVENTH BIENNIAL
REPORT

1927-1928

RIBUNE PRINTING CO. tl^^^^HD GREAT FALIS, MONTANA

MONTANA STATE BOARD OF ENTOMOLOGY

W. F. Cogswell, M. D., Secretary State Board of Health,
Chairman, Helena, Montana.

W. J. Butler, D. V. S., State Veterinary Surgeon,
Member, Helena, Montana.

J. E. Parker, M. S., Acting State Entomologist,
Acting Secretary, Bozemau, Montana.

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LETTER OF TRANSMITTAL

Bozeman, Montana, December 15, 1928.

To His Excellency,

John E. Erickson, Governor,

Helena, Montana.

Dear Sir :

As acting secretary of the Montana State Board of Entomology I have
the honor of submitting the Seventh Biennial Keport which covers the calendar
years of 1927 and 1928.

Outstanding developments of this period have been the completion of the
new laboratory at Hamilton, the success of the Spencer-Parker vaccine in
preventing Kocky Mountain Spotted Fever, and the rearing and liberation of
the Trench tick parasite, Ixodiphagus caucurtei. Papers dealing with these
developments will be found in the body of the report.

Kocky Mountain Spotted Fever has continued to spread throughout the
state. Whereas the disease was formerly largely confined to Western Montana
it has now been reported from 23 counties in Eastern Montana involving an
area of more than 30,000 square miles. During the biennium 15 cases occurred
in the western half of the state and 49 in the eastern half. The problem of
Rocky Mountain Spotted Fever is therefore extremely vital to the welfare of the
entire state and warrants the continued support of state funds.

Respectfully yours,

J. R. Parker, Acting Secretary.

CONTENTS

Page

FOEEWOED 7

EOY KEELEE 9

TICK PAEASITES 10

Tick Parasite — Executive Eeport 10

Preliminary Eeport on the Tick Parasite,

Ixodiphagus caucurtei du Buysson 17

Quantity Production of Tick Parasites 32

Tick Parasite Liberation in Montana During 1928 35

EOCKY MOUNTAIN SPOTTED FEVEE 39

Eoeky Mountain Spotted Fever 39

Eoeky Mountain Spotted Fever in Montana, 1927-1928 63

Vaccination Against Eoeky Mountain Spotted Fever 68

A Short Eeview of the Work of the U. S. Public Health Service on

Eoeky Mountain Spotted Fever 69

Control Work: Eoeky Mountain Spotted Fever Control Districts,

Bitter Eoot Valley, 1927-1928 70

TULAEAEMIA AND TICK PAEALYSIS 76

Introduction 76

Eesults of Preliminary Investigations in Montana of Pathological
Conditions in Sheep Due to the Wood Tick, Bermacentor ander-

soni Stiles 77

MONTANA LABOEATOEY FOE THE STUDY OF INSECT-BOENE

DISEASES 86

STATE BOARD OF ENTOMOLOGY

FOREWORD

J. R. Parker. Acting Secretary

According to the wordiug of the creative legislative act it is the duty of
the Montana State Board of Entomology "to investigate and study the dis-
semination by insects of diseases among persons and animals, said investiga-
tion having for its purpose the eradication and prevention of such diseases."
The study of insects which do not transmit disease and the control of insects
attacking crops are therefore not within the province of this board but are
taken care of by the Agricultural Experiment Station and the State
Entomologist. The State Board of Entomology is composed of three members;
the Secretary of the State Board of Health, the State Veterinary Surgeon and
the State entomologist, and therefore brings together in one organization the
three State Officials who are most concerned with the control of human
diseases, animal diseases and insects which may transmit disease.

The field headquarters for the Montana State Board of Entomology is at
Hamilton, Montana, where a modern, fire-proof, well equipped laboratory
was built tliis past year with funds provided by the 1927 legislative session.

The laboratory is occupied jointly by two staffs of investigators, one
employed by the Montana State Board of Entomology and the other by the
U. S. Public Health Service. These two organizations have worked together
under an informal plan of co-operation since 1921. The State Board of
Entomology has been fortunate indeed in securing this co-operation; the U. S.
Public Health Service has not only been generous in its financial support of
the work but has also provided higlily trained investigators whose researches
have advanced the work far more rapidly than could have been expected if
the State Board had continued to work alone.

The personnel of the State Board of Entomology remained unchanged
from the time the Board was established in 1913 to March, 1928. These fifteen
years of continuous service by all members of the Board have resulted in a
continuity of effort and an effectiveness that could not have otherwise been
obtained. In March, 1928, Professor R. A. Cooley, Secretary of the State
Board of Entomology, was granted a year's leave of absence from his duties
at the Montana State College and the Agricultural Experiment Station. He
is spending the year searching for tick parasites in South Africa and studying
ticks and tick parasites in England and France. The object of his trip is to
obtain information that will be valuable to the State Board of Entomology in
its efforts to control ticks in Montana by the use of parasites. Professor
Cooley is making his trip without expense to the State, personally paying part
of his travelling expenses, the remainder being paid from money contributed
by organizations interested in the possibility of tick control by parasites. In
this connection the Board of Entomology is pleased to acknowledge the
financial aid extended by the Anaconda Copper Mining Company, the Mon-
tana Power Company, the Great Northern and the Northern Pacific Railroads.
Professor Cooley will return to Montana in March, 1929, and will at that time
resume his duties as Secretary of the State Board of Entomology. During his

8 SEVENTH BIENNIAL REPORT

absence J. E. Parker, of the Montana Agricultural Experiment Station, is
serving as Acting Secretary.

The main lines of work conducted by the State Board of Entomology staff
during the past biennium were the study, rearing and liberation of the tick
parasite, Ixodiphagus caucurtei duB., and the continuation of the tick con-
trol program carried on in the Bitter Eoot Valley since 1918. Studies in con-
nection with the preparation and use of a vaccine to prevent Eocky Mountain
Spotted Fever and investigations concerning the organism causing the disease,
have largely occupied the attention of the U. S. Public Health Service workers.
A more detailed account of the work together wth some of the results accom-
plished, will be found in the body of the report.

As acting secretary of the State Board of Entomology, I wish to grate-
fully acknowledge the aid given by Doctor E. E. Parker and Doctor E. E.
Spencer in supplying material for the Biennial Eeport covering the work of
the U. S. Public Health Service at the Hamilton Laboratory during the past
biennium.

STATE BOARD OF ENTOMOLOGY

ROY KERLEE

To the list of those who have given their lives in the study of Eocky
Mountain Spotted Fever, another name must be added. While employed as
assistant bacteriologist in the Hamilton Laboratory, Eoy Kerlee in some un-
known manner contracted the disease and died on February 14, 1928.

Arthur LeEoy Kerlee was born at Darby, Montana, March 5, 1905, and
received his early education in the Darby schools. He graduated from the
Montana State College in 1927 with the degree of bachelor of science in
Botany and Bacteriology. Following his graduation he was employed as
assistant bacteriologist by the U. S. Public Health Service in the Hamilton
Laboratory. While in college Kerlee was a fine student and a leader in many
campus activities. Knowing full well the dangerous nature of the organism
which he would be called upon to study, he entered upon his ^professional work
with fearless enthusiasm. Although at the time of his death he had been
engaged in research work for only a few months, he was looked upon as a
young man of unusual ability who, if he had lived, would have gone far in
his chosen profession.

10 SEVENTH BIENNIAL REPORT

TICK PARASITES

TICK PARASITES— EXECUTIVE REPORT.^)

By
R. A. COOLEY, Secretary, Montana State Board of Entomology

111 the Sixth Biennial Eeport of the Montana State Board of Entomology
it was stated that the so-ealled French tick parasite (Ixodiphagus caucurtei du
Buysson) had been brought to Montana and that the work of colonizing it
here had been started in the hope that in time it might be found to be an
important factor in the destruction of the prevailing tick of the region
(Dermacentor andersoni Stiles). It should be stated, clearly, that our exper-
iences with the parasite so far have been distinctly encouraging, although
some difficulties have appeared which will have to be overcome.

In order to lead to a clearer understanding of what is involved in an effort
to introduce such a parasite, the necessary procedure will be outlined. The
purpose of the experiment is to breed -the parasites in quantity and to liberate
them where the ticks occur in Nature, and by such methods as will make it
possible for them to take up their habit of parasitizing the tick. The primary
requirements for successfully carrying out the enterprise are the following :

1. Keeping the parasites alive in the laboratory and breeding large
quantities when they are needed, particularly in the spring when they are to
be liberated.

2. Growing a sufficient supply of non-infected ticks in which to feed
the parasites.

3. Holding a sufficient supply of caged animals on which to feed ticks
both in growing our supply of ticks and for use in feeding ticks while they
are being parasitized.

4. Experimental work and study in order that we may better under-
stand this little known parasite whose habits are perhaps not primarily adapted
to the physical and biological conditions found in Montana.

5. Enough employees to carry out the tremendous amount of detail
required in the work.

6. Equipment such as animal cages, cage racks, infesting bags, micro-
scopes, as well as vials, pill boxes and scores of items of petty equipment.

7. Transportation to and from remote localities in the mountains, and
to and from other parts of the state where effort is being made to colonize
the parasite.

Previous to getting our initial stock of living parasites from Doctor
Larrousse in July, 1926, no provision had been made for getting a supply of
ticks in which to feed the parasites in the laboratory, and without such ticks
the parasites could not be materially increased. However, at that season of
the year we would not take steps to increase our supply, for it is necessary to
begin with adult ticks in the spring. These considerations in turn made it
impossible to liberate very many parasites in the spring of 1927. In the spring
months of 1927, steps were taken to obtain a supply of fully fed female ticks,
fresh out of nature and in a normal, vigorous condition. These were obtained

<1) Submitted by Professor R. A. Cooley on March 1, 1928, prior to his leaving
for South Africa.

STATE BOARD OP ENTOMOLOGY 11

from a locality near Flathead Lake believed to be free of any infection with
human diseases. These females laid eggs which were incubated in thermal
cabinets, and the larval ticks which hatched were fed on laboratory animals.
When they dropped, fully fed, they were recovered from the ' ' infesting bags ' '
and were incubated. About 250,000 nymphs were thus obtained from the
fed larvae by September, and are our stock of ticks for maintaining the stock
of parasites and for the quantity liberations in the spring of 1928.

In the season of 1928 it will be necessary to again rear a supply of
nymi:)hal ticks for 1929 and to rear large quantities of the parasites for
liberation.

The procedure of rearing parasites is as follows :

In the early spring the nymphal ticks are brought in from the stock
out of doors where they have been held in tubes or cages under conditions as
nearly natural as possible, and put on laboratory animals together with living,
adult parasites which lay their eggs in the ticks. The ticks continue to feeS
to repletion and drop off in the infesting bags. They are recovered and held
at favorable temperatures in thermal cabinets. Those ticks which have been
parasitized show up and are picked out and put individually in "tubes"; the
others, not parasitized, develop normally and produce adult ticks.

In order to make the best use possible of the French parasite a large
amount of experimental work and study has been laid out. The principal sub-
jects under investigation are the following:

1. Can the parasite endure the severe climate of Montana? A few para-
sites were placed out of doors in the fall of 1926 and were examined in the
spring of 1927 and found to be all dead. In the light of later findings not
much importance is attached to this, however, as we do not yet know what the
normal stage of the parasite in hibernation may be. Parasites in a full state
of nature, having fed in ticks in nature, may adopt means for hibernation of
which we have no knowledge. In the summer and fall of 1927 numerous para-
sites in various stages of development were placed out for observation under
a variety of field conditions, and in the spring of 1928 we may have results
of value.

2. Can this parasite adapt itself to the habits of our wood tick? We
cannot say positively what part of the world the parasite came from nor what
its original tick host or hosts may have been. There is a considerable varia-
tion in the habits of ticks and much may depend on the adaptability of the
parasite. We have given careful attention to the effects of various tempera-
tures on the development of the parasite and to the responses to biological
factors, and some observations of great interest have been made. The parasite
feeds only in the fed nymph, so far as we have yet been able to discover. It
follows, then, that the parasite can multiply in nature in Montana only during
those spring and early months when the nymphs are feeding on their rodent
hosts. This season is mainly over by July 15, though a lesser number may be
found until about September first. It is possible that the parasites which,
with favorable temperatures and a supply of nymphs to lay their eggs in, are
capable of passing through several generations during a summer, may die off,
wholly or in part, if unable to find ticks in which to lay their eggs. This, if
true, would be very unfortunate, but already we have found substantial indi-
cations of an adaptation, hitherto unsuspected, which may wholly obviate this
difficulty.

12 SEVENTH BIENNIAL REPORT

3. Is there another tick in Montana which the parasite can use as a host
during the late summer and early fall, and what would be the effect of such
a secoudary host on the parasitism in the wood tick? Instances are common in
nature in which a secondary host is of much value in completing the needs of
a valuable parasite. We have other ticks in Montana the life histories of
which should be studied in this connection. Dependent upon developments in
the future we intend, if possible, to make such studies.

4. How rapidly may the parasite multiply and overcome the ticks in a
given locality? It is of much practical interest to know not only if the para-
site can survive our climate, both in summer and in winter, and adapt itself
to the habits of our ticks, but also to know how rapidly it is able to increase
to effective numbers. On this would depend to a considerable extent our de-
cision whether to liberate more or less parasites in any one locality. If fewer
are to be placed in one colony, more colonies can be started. Accordingly,
experiments have been started the purpose of which is to determine from
year to year the percentage of parasitism in each colony established.

5. How far and how rapidly can the parasites spread from a given center
of introduction? Again, it will be of interest to know whether from a given
center of distribution the parasites will spread by their own means over many
miles in say five years, or remain rather closely confined to the locality where
originally introduced. Field men will collect ticks at measured distances by
shooting and trapping their rodent hosts, and bring them to the laboratory
where they will be held under observation for parasitism. It is assumed that the
rapidity and distances will vary with the kinds of animals which are tick
hosts in the several localities. Some animals, such as rabbits, should spread
the parasites rapidly and far.

6. What is the most effective or least expensive method of liberating
parasites? The laboratory method of parasitizing ticks is to turn the newly-
emerged parasites loose in a closed bag of unbleached muslin with a small
animal, usually a rabbit or a ground squirrel, on which ticks in the nymphal
stage are feeding. The parasites hunt the ticks in the fur and around the
eyes and ears and lay eggs in them. It is assumed that the parasites have
a similar habit on wild animals out in nature. In liberating the parasites it is
our purpose to place them where they can find animals and ticks. It is, of
course, necessary to place the parasites out at the right time of the year. At
the start, there was very little information to guide us in determining the best
method. A series of experiments has been started for the purpose of getting
this information. Following are some of the methods that have been tried:

a. Capture wild rodents and infest them with nymphal ticks in the
laboratory and after paiasitizing the ticks turn the animals loose again in the
same locality where they were captured. It is expected that in this way
parasitized ticks will be dropped in the very localities where we want them
to be, and that the parasites when mature and ready to lay eggs may find the
ticks on other ani)uals.

b. Mountain rats abound in the vicinity of the "goat rocks" where the
mountain goats are abundant and where the ticks are plentiful. Mountain
goats are undoubtedly a very important host of adult ticks. It is well known
that mountain rats, or pack rats as they are sometimes called, delight in pick-
ing up and carrying off objects that human beings leave around. Ground
squirrels also do this to some extent. A piece of rag or cotton is attractive

STATE BOARD OP ENTOMOLOGY 13

to them. Vials or "tubes" containing parasites, so arranged that the para-
sites can escape when they emerge or when disturbed, are attached to small
balls of cotton. In their night wandering the pack rats, and during the day
the ground squirrels, find these and carry them to their nests.

c. During the winter and in the early spring rabbits often find diffi-
culty in getting enough food. Another experimental method is to establish
feeding places where the rabbits gather and form a habit of returning. After
the rabbits have become accustomed to the place, parasites are liberated in
the immediate vicinity surrounding the feeding place so that the parasites
can find the ticks on any animals that come for food.

d. Place tubes about to yield adult parasites in the vicinity of the nesting
places and haunts of the various rodent hosts of ticks, such as mountain rats,
woodchncks, ground squirrels, pine squirrels, chipmunks, and rabbits.

e. Pull the cotton plugs and leave tubes of parasites in the grass in likely
places where, by chance, rodents may pass.

Our work on ticks in previous years has taught us that in different locali-
ties the rodents vary in importance as hosts of the early stages, and hence as
producers of adult ticks which are to feed on the larger animals, wild and
domestic. Since, in the mountainous country in Eavalli County, mountain
goats are abundant and undoubtedly feed very large numbers of adult ticks,
it naturally is of interest to discover what the rodent hosts are and then to find
a way to cause the parasites to attack the ticks on them in particular. Special
attention is being given to this point and since we know that the mountain
rat is one of these hosts of young ticks in the "goat rocks," and perhaps,
the principal one, parasites are being placed in their haunts.

What Progress Is Being Made With Parasites?

It should be stated quite plainly that it is too early to state what the
results of the work so far done on parasites may be. It will be doubtless
many years before the full results may be known. However, in a few years
Ave may have enough information to indicate rather reliably what the eventual
results are liable to be. It should be borne in mind that the work is new and
that there is only a very little of experience to guide us; that the State is
large; that it may require time for the parasites to become progressively
adapted to the new conditions; that the labor of breeding the parasites in
quantity is tremendous; and, finally, that these small insects which may die
off largely each winter, as most other insects do, may require years to multiply
and spread. We realize that since Ave are entrusted with the expenditure of
public funds it is necessary that we be informed as early as possible regarding
what the local results of parasite liberation may be, so that we may judge
reliably Avhether or not progress may be expected.

Origin of Tick Parasites.

A study of all that is knoAvn regarding this very small and highly special-
ized group of tick parasites has shown it to be very probable that it originated
in Africa. We belieA'e that the three known species all came from that conti-
nent, and yet no special effort has ever been directed at finding tick para-
sites there, although much work on the ticks of Africa has been done. The
tick parasites that we know of all have been discovered by chance in connec-
tion with other work. Plainly, it is desirable to make a search for other
species of tick parasites in Africa. Having noAV to our advantage a knowl-

14 SEVENTH BIENNIAL REPORT

edge of how to look for tlipiii, there is a reasonably good chance that by going
to the right places and looking in the right way, we may discover other species
that may be introduced into Montana. We cannot venture an opinion
either as to what the habits of such a new species may be or how the habits
may vary from those of the parasites we now have, but other species of para-
sites of different habits, in combination with those species we now have, may
be of the greatest value to us.

Again, it is very desirable to study the habits of these parasites in their
native environment and on the same hosts they have been using for countless
years. The habits of their tick hosts should be studied and correlated with
the parasite's habits. It is believed that information of this character may
be of great value to us. We know that in 1909 Mr. C. W. Howard discovered
what we have called the Texas species, in Portuguese East Africa, and I have
a-ecently learned through Mr. C. P. Lounsbury of Pretoria, Transvaal, that
some years ago parasites were recovered in Natal from some ticks that were
under observation. These parasites are now in a museum in South Africa and
have never been studied. They may be new.

It is for these reasons that the writer in taking his sabbatical leave from
the University, has decided to go to South Africa for the purpose of studying
tick parasites. The expedition may be briefly outlined as follows: Leaving
New York on April 12, 1928, the first stop will be made in England where
some time will be spent with Doctor George H. F. Nuttall at Cambridge, a
prominent authority and writer on ticks, who has very large collections and
who has done field work on ticks in Africa. It is very desirable, so far as
possible, to recognize ticks as they are collected and the time in England
will be spent in studying Doctor Nuttall 's collections. In France some time
will be spent in the study of ticks with Doctor E. Brumpt in Paris, who also has
extensive collections and has collected and done field work in Africa. Particu-
lar attention will be given to the French parasite of ticks for it was in
Doctor Brumpt 's laboratory that the species was studied. As much informa-
tion as possible will be obtained on the habits of the parasite in nature, its
seasonal history, and in correlating its habits with those of the tick it preys
upon in France.

In South Africa it is expected that laboratory facilities will be obtained
in one of the Government laboratories and that the work will be a combina-
tion of field and laboratory studies. The major part of the work will be in
the field where the hosts of the early stages of ticks will be shot or trapped
and examined for ticks. Any ticks recovered will be taken to the laboratory
for study and an effort will be made to find a way to bring them to America
alive.

A Second Tick Parasite.

Knowing that Ijack in 190S a tick parasite (HuntereUus hookeri Howard)
had been discovered in Texas by workers in the U. S. Bureau of Entomology
and 'described by Doctor L. O. Howard, a letter was written to Mr. F. C.
Bishopp, who at that time was in charge of the branch laboratory of the
Bureau at Dallas, Texas, asking if a supply of living parasites of the Texas
species might be obtained through him. Mr. Bishopp very kindly sent me two
lots of ticks {Bhipicephalus sanguineus Latreille) collected at Brownsville,
Texas, stating that they would probably yield some parasites. A total of 192

STATK BOARD OF ENTOMOLOGY 15

nyniphal ticks were received and 13 of these yielded adult parasites, or 6.7
percent. Thus we came into possession of a second" living tick parasite, though
our supply was small and precarious.

A laboratory study of this parasite was made by Mr. H. P. Wood of the
Bureau of Entomology and an article was published in The Journal of Eco-
nomic Entomology'^). This was the first published article on the habits of a
parasite of this group and contained much information of value. A study
of this article reveals that the habits and life history are remarkably like those
of the French species, as later published by Doctor Brumpt, and as further
studied by us. Mr. Wood was able to cause it to parasitize the American Dog
Tick (Bhipicephahis sanguineus Latreille) but he was unal)le to cause it to
develop in our northern tick (Dermacentor andersoni Stiles), or in any other
tick. Mr. Wood also sent some of the living parasites to Mr. C. P. Lounsbury
in Cape Town, South Africa; C. W. Howard, Loureneo Marquez, Portuguese
East Africa, and to P. Silvestri, Portici, Italy. In no case were these workers
successful in their attempts to rear the parasites on ticks.

Our supply of living parasites from Texas was sent over to the Hamil-
ton laboratory. Mr. Glen Kohls, who was locally in charge of the parasite
work, undertook to rear them on our wood-tick or Spotted Fever tick, adopting
the same .methods that are used in rearing the French species. For all time
we must give credit to Doctor Brumpt for, with great labor and at much ex-
pense, having worked out a way of keeping the French species alive in the
laboratory and cavising it to breed and multiply. During something over thir-
teen years he must have kept a strain of this parasite alive, for he published
on it in 1913 and sent living insects to Naushon Island, Massachusetts, in 1926.

Mr. Kohls ' efforts were successful. While at first the insects did not
lay eggs freely in the wood tick, successive generations took more readily to
the new habit and now (February, 1928) in less than one year, there appears
to be no more difficulty in keeping the species alive in the laboratory and in
causing it to multiply at will than in the French species.

Clearly the two S2)ecies are closely related and very much alike in their
habits, and the fact that H. hookeri Howard has been accommodating enough
in so short a time to modify its habits for us is very encouraging, for it is
very likely tiiat it may be very desirable to modify the habits of both species in
other respects in order that they meet our needs.

We are now able to multiply both species at will in the laboratory, the
only limitations appearing to be the supply of ticks and the labor necessary,
and since the uymphal ticks can be reared in the laboratory if enough labor
is employed, the number of parasites is limited only by the money expended.

We cannot emphasize too strongly the necessity for an extended study of
all the factors that have a bearing on the parasite problem. We must know
as much as possible about the habits of the parasites, the habits of the ticks,
the habits of the animals that are tick hosts, effect of climate and numerous
biological factors, and be constantly guided by new findings. Before liberat-
ing a second parasite in nature, it will be necessary to determine as accurately
as possible what the effect will be on the first species liberated. Instances are

(2) Wood, H. P. "Notes on the Habits of the Tick Parasi!.e Hunterellus hooJceri
Howard." Journ. Econ. Ent. IV, 1911, pp. 425-431.

16 SIOVEXTH BIEXNIAL REPORT

on record in which mistakes have been made by liberating parasites before
determining their habits. We shall not at present liberate the Texas species
in Montana but shall first make a careful study of it in the laboratory.

More Than One Parasite Desirable.

It is apparent that it is desirable to have more than one species of tick
parasite operating on our wood-tick just as it is desirable to have more than
one insectivorous bird feeding on our insect pests. Different parasites working
in different ways or at different times of the year, or even all working in the
same way, would be an advantage. Much experience on other insect pests in
other states and countries confirms this opinion. The standard practice is to
introduce as many as possible of the parasites that appear to promise benefit.
Hawaii leads the woj'ld in the control of insect pests by the use of parasites,
and, in an effort to control relatively very few troubles, has introduced upward
of ninety parasites and predators. It is commonly said of Hawaii that "para-
sites have saved the Islands, ' ' which is literally true.

Montana, then, in attempting to bring the tick menace under control by
the use of parasites, and in seeking for other species, even in Africa, is follow
ing standard methods and is backed by abundance of precedent.

Where Parasites Are Being Liberated in Montana.

The liberation of parasites was begun in the spring of 1927, in the moun-
tain canyons bordering on the Bitter Root Valley in Eavalli County. As has
been explained above, only a limited number of parasites was liberated during
that year because wc did not have the nymphal ticks on which to feed the
parasites and could not get them without rearing them in the laboratory from
adult ticks obtained in the spring. During the spring and summer of 1928
greatly increased numbers of parasites will be liberated in Eavalli County and
colonies will be started in the lower Bitter Root Valley and in the mountains
adjacent. As rapidly as conditions warrant and we are able to do it, other
colonies will be started in various parts of the state.

The following localities have been provisionally decided upon for new
work during 1928: In the upper part of the LoLo Valley; in upper O'Brien
Creek, west of Missoula ; in Owl Canyon four miles northeast of Bozeman ;
near Helena; in Musselshell County; near Miles City and Forsyth in eastern
Montana; in Carbon County, and in either Fergus County or Garfield County.
By referring to a map of the distribution of cases of Rocky Mountain Spotted
Fever in another part of this report, it will be observed that the locations for
parasite colonies have been selected where a considerable number of cases of
Spotted Fever have occurred. It will be quite impossible to give as much at-
tention to these scattered colonies as will be given to localities close by the
laboratory. In the process we hope to learn what measure of success may be
expected from such more or less hasty attempts in remote places. Until we
have gotten much more information on the liabits of the parasite and on meth-
ods, it will be necessary to concentrate our efforts mainly on the experimental
colonies close bv the Board's Laboratorv in the Bitter Root Vallev.

STATE BOARD OP ENTOMOLOGY 17

PRELIMINARY REPORT ON THE TICK PARASITE,
IXODIPHAGUS CAUCURTEI DU BUYSSON.

By

K. A. COOLEY, Secretary, Montana State Board of Entomology^'^>

Review.

The three known Chalcidid parasites of the Ixodoidea constitute a tribe,
the Ixodiphagini, belonging to the sub-family Eneyrtinae and family Encyr-
tidae. The genera and species are as follows:

Ixodiphagus texanus Howard
Hunterellus hool'eri Howard
Ixodiphagus caucurtei du Buysson

In ]907 Doctor L. 0. Howard(2) described the first known Chalcidid
parasite of a tick, Ixodiphagus texanus, from specimens reared from nymphs
of HaemaphysaUs leporis-palustris Pack., which were received on March 15,
1907, from Mr. J. D. Mitchell, Victoria, Texas. The ticks had been taken from
a cotton-tail rabbit and a jack rabbit.

In 1908 Doctor Howard described the second species, Hunterellus
hooker'J-'l, from specimens reared by W. A. Hooker from numerous nymphal
specimens of the Brown Dog Tick, Bhipicephalus texanus Banks, which has
been collected by Mr. H. P. Wood from a Mexican dog on April 20, 1908, at
Corpus Christi, Texas.

In 1912 the learned French entomologist, R. du Buysson (4), described
Ixodiphagus caucurtei from specimens discovered by the eminent E. Brumpt,
Professor of Parasitology of the Faculty of Medicine of the University of
Paris. Doctor Brumpt 's specimens were reared from nymphs of Ixodes ricinus
Linn., which he had taken near Paris at Chantilly and Fontainebleau from deer.

Regarding the first species described (I. texanus) nothing has been con-
tributed since the original publication. This insect has never been
re-discovered.

Mr. H. P. Wood(5) in 1911 published the results of a laboratory study
of H. hookeri and recorded important findings. He records the surprising fact
that C. W. Howard had found the same species of parasite attacking nymphs
of Bhipicephalus sanguineus Latr., at Lourenco Marquez, Portuguese East
Africa, in 1909. By letter dated February 1, 1928, I have learned from Mr.
C. W. Howard that his specimens of jff. hooTceri were reared from Bhipi-
cephalus evertsi taken from a dog. The letter further states that the para-
sites emerged from the adult ticks. This is surprising and is the only case on
record of tick parasites emerging from adult ticks. The parasites were very
numerous and were found in only one lot of ticks. Identification as R. hoolceri
was made by Doctor L. O. Howard.

(1) Submitted by Professor R. A. Cooley on March 1, 1928, prior to his leaving
for South Africa.

(2) Howard, L. O. "A Chalcidid Parasite of a Tick." Ent. News XVIII,
pp. 375-378, 1907.

(3) Howard. L. O. "Another Chalcidoid Parasite of a Tick." Can. Ent. XL,
pp. 239-241. 1908.

(4) DuBuvsson, R. "Un Hymenoptere Parasite des Ixodies." Archives de Para-
sitologie XV, p. 24 6, 1912.

(5) Wood, H. P. "Notes on the Life History of the Tick Parasite." Journ.
Econ. Ent. IV, pp. 425-431, 1911.

18 SEVENTH BIENNIAL REPORT

Mr. Wood states that two nymphs of Dennacentor parumaperttis margin-
atus Banks were taken "on a jack rabbit (or dog)" by Mr. McClure Lewis
of Green Valley, California, and received at the Bureau's Dallas laboratory
on June 18, 1910. One of these yielded H. hookeri. The author records the
following additional localities where H. Jioolceri had been taken: Brownsville.
Texas, and Monterey, Mexico. Of the Monterey specimens it is stated that the
adult parasites were never obtained and that the identification had been made
from immature specimens. If another species of tick parasite is ever found
in that locality this identification must be brought in question.

To the records of geographical distribution of H. hookeri as given above
are to be added the following, very kindly given to me by Mr. S. A. Eohwer
of the U. S. National Museum :

1. Coimbatore, South India, February, 1921, on bull terrier dog (E. Bal-
lard and Fullaway) dot. Timberlake.

2. Two slides in tray with above, but slides not bearing determination.
Indo-China. Bred from dog tick (E. Eoubaud). Letter Feb. 17, 1913.

3. V^edado Havana, Cuba, ex nymphal ticks. (Dr. Etchegoyhen). Ee-
ceived from N. S. Mayo. Det. Gahan.

Mr. Wood found that mating takes place immediately after the parasites
emerge and that the females are ready at once to lay eggs in fresh ticks. To
larval ticks the parasites were found to pay no attention though the record
does not state whether the larvae under observation had been engorged.
Attempted oviposition was observed in a male and an uneugorged female of
R. sanguineous. It was believed that "all that the parasite requires is a
nymph at least partly engorged". Adult parasites were seen to imbibe sweet-
ened water. In eight to fifteen days a characteristic striped appearance in
parasitized nymphs became evident and in about forty-four days the adult
parasites emerged.

The number of parasites per tick was found to vary between three and
seventeen and the females were more numerous. The number of days required
to emerge varied between 20 and 67, though the temperature was not recorded.

The Avriter was successful in his attempts to rear the parasites artificially
on E. sanguineus, though only one generation was reared. It was suspected
that more than one egg was laid at a single insertion of the ovipositor as more
parasites than the number of insertions were observed to emerge when mature.
Attempts to parasitize other species of ticks were unsuccessful.

In a stimulating and very valuable paper published in 1913, Doctor
Brumpt records certain of his studies on I. caucurtei. In a certain case 17 out
of 100 nymphs of /. ricinus recovered from deer were found to be parasitized,
and in another, 10 out of 100. At Fontainebleau 2 nymphs of Haemaphysalis
concinn.a Koch were found parasitized. Experimentally he was able to para-
sitize 95 out of 100 of /. ricinus; 90 out of 100 of B. sanguineus and 100 out
of 100 of D. andersoni Stiles. The last named species is our wood-tick of
Northwestern United States.

In France the adult parasites are to be seen from April to November.
This author also finds that the parasites attack only the nymphs of ticks,
either unfed or engorged, and complete development takes place in 4 to 6
weeks. In captivity the life of the adult parasite is not to exceed 8 days.
No hyperparasites were found. Above a certain amount humidity was found
to be very unfavorable. It is stated that the tick, B. sanguineus, is rarest in

STATE BOARD OF ENTOMOLOGY 19

France where tliis parasite is present and the author believes that the para-
site is responsible. Doctor Brumpt particularly discusses the wood-tick and
keenly analyzes the biological factors concerned and urges the desiraljility of
attempting to control it by the use of the French parasite.

The foregoing summarizes rather completely all that has been published
regarding tick parasites, with the exception of brief notes published m the
Sixth Report of this Board which gave an account of the introduction of
/. caucitrtei into America, and preliminary notes published by the present
writer. (*>)

Summary of Published Records.

The following primary- facts, which throw a considerable amount of light
on these valuable parasites, may be gleaned from the record. Three species
of tick parasites have been discovered, two from Texas and one from France.
All are alike in having been found feeding in nymphal ticks only and the
parasitized nymphs were all found feeding on their host animals. One excep-
tion must be recorded, that of Mr. C. W. Howard 's finding of parasites in
adult ticks. The Texas species were both taken in the spring and the French
species in the fall. The ticks from which the parasites were reared are H. le-
poris-palustris, H. texanus, R. evertsi, R. sanguineus, I. ricinus and D. paruma-
pertus timrginatus. Since being brought to America /. caucurtei has also been
reared in D. andersoni and Dermacentor variabilis Say. The host animals of
parasitized ticks taken out of nature are cottoiitail rabbits, jack rabbits, dog
and deer, exclusive of laboratory animals at the Hamilton Laboratory.

The Egg and Egg Laying.

So far as the printed records show, the eggs of tick parasites have never
been observed. As a preliminary to a search for eggs in parasitized nymphal
ticks, the ovaries removed from females of /. caucurtei were smeared on a slide
and stained with Giemsa's stain when the very numerous eggs became ap-
parent. The egg is broadly ellipsoidal, 0.06 mm. in length and without mark-
ings. To one end is attached a stem or egg-stalk. This stem is not always
evident in smears but may be coiled against the end of the egg where it ap-
pears as a small eccentric protuljerance. See figure 6. The dorsal walls
of the several slightly fed nymphs were removed, cleared and mounted. An
examination showed the punctures made by the ovipositors but we have not
been able to demonstrate the eggs in the ticks.

Our method of rearing parasites in the laboratory was learned from Doc-
tor Larrousse on Naushon Island in 1926, and essentially the French method
has been used ever since with some modifications. The newly emerged adult
parasites are liberated from very small vials on laboratory animals which
have been previously infested with nymphal ticks. Some observations have
been made on the habits of the parasites in depositing their eggs. The para-
sites appear to be well adapted to finding the ticks in the fur of the host
animal and in such nearly bare places as in the ears and around the eyes. The
objects of their search are recognized at once and generally the ovipositor is
inserted almost inmiediately on finding a victim. The act of ovipositing
takes but a few seconds, and a parasite after ovipositing once in a tick gen-
erally goes away in search of another, though rarely the act is repeated in the
same tick. Two parasites have been observed ovipositing in one nymph at

(6) Cooley, R. A. "Tick Parasites." The Med. Sentinel, XXXV, (1927),
pp. 805-815. (Portland, Oregon).

20 SEVENTH BIENNIAL, REPORT

the same time, aud it is not uncommon for more than one female to lay eggs
in one nymph. Mr. Kohls C) placed one female parasite with one unfed nymph
in a small vial and watched them for two and one-half hours, during which
period he observed the insect to insert the ovipositor in the tick forty-seven
times. The observation was then discontinued. Doctor Brumpt found that
at each insertion of the ovipositor the female lays from 5 to 10 eggs. Mr.
Wood in his study of H. hookeri reports having found 13 parasites in a nymph
that "had been parasitized only about three times — in no case as many as 13
times. ' ' No exact work has been done to determine how many eggs a female
may lay but the number must be large for she works rapidly and the supply
of eggs in the ovaries is very large.

Egg Laying in Fed Larvae.

In the summer of 1927 Mr. Kohls conducted an incidental experiment
that yielded very interesting results. The supply of nymphs of D. andersoni
is produced by feeding larval ticks on laboratory animals. There is thus
a plentiful supply of fed larvae on hand during the summer months. One
pill box of recently fed larvae, which had dropped on August 20 and amount-
ing to about 350, were placed in a small glass jar with about 90 adult /. cau-
curtei (males and females mixed) and set in the sunshine at room temperature
for a period of 3 hours. Following the exposure to parasites they were placed
in a thermal cabinet at 19°C., which is the usual procedure for rearing ticks.
By September 22 all of these fed larvae had "molted" to the nymphal stage.
They were then put in a longevity tube and placed out of doors in the ' ' tick
yard" under conditions simulating nature. On November 11 these nymphs
were put on a rabbit in the laboratory for feeding. In order to activate the
nymphs they had been brought into the laboratory two weeks earlier and held
at room temperatures. Seventy-eight fed nymphs recovered from the rabbit
were placed at 19 °C. and were examined from day to day. On December 5
it was noted that several showed the characteristic mottling indicating para-
sitism and eventually 32 nymphs, or 41.02 per cent of the whole number, were
isolated as parasitized. From these, 9 yielded adult parasites in due time.
"While 9 out of 32 is a small number to come through to the adult condition,
there may be and there may not be special biological significance in the fact
for it has been found that occasionally a lot of parasites which appears to be
normal may fail to emerge and we attribute the failure to faulty conditions
of humidity or temperature.

The foregoing shows that under the conditions stated;

a. /. caucurtei will lay eggs in freshly fed larvae of D. andersoni.

b. While it is true that in the case of eggs deposited in nymphal ticks,
development of the parasite begins promptly in suitable temperatures and
will proceed to the maturing of the parasites, in the case of eggs deposited
in fed larvae the development is delayed.

c. The living parasite is carried through the quiescent period of the fed
larva and is alive in the next stage.

d. The 'parasite remains alive through a resting period of the unfed
nymph prolonged for 50 days (September 22 to November 11).

e. Upon the nymph being fed the parasites will develop to maturity.

(7) Mr. Glen M. Kohls, a Junior in Entomology at Montana State College, was
employed by the Board of Entomology for one year beginning April 1, 1927,
and was placed in local charge of parasite work at the Hamilton Laboratory.

STATE BOARD OF ENTOMOLOGY

21

Egg Laying in Other Tick Stages,

It is well established that, under laboratory conditions at least, adult
females of the French species will lay eggs freely on nymphs of various
species of ticks while the latter are attached to host animals. It may be
the usual habit of the parasite to seek out tick hosts and to search them for
nymphal ticks. Such a habit is strongly indicated as the normal one. In the
practical work of establishing colonies of parasites, however, it would appear
to be unwise to neglect the possibility that there are other ways in which
eggs are normally laid. In fact, the information so far gained points to the
desirability of experiments and studies that will reveal much more regarding
the habits of these insects. It is particularly desirable to determine if there
are adaptations by which the species may survive periods of the year when
nymphal ticks are not to be found on their hosts. We now know that when
confined in vials the female will lay eggs in fed larvae, flat nymphs and fed
nymphs. Wood has observed attempted ovipositiou ' ' in both a male and un-
engorged female of li. sanguineus." Mr. Wood does not state whether these
adults of B. sanguineus were later fed and observed for parasitism. It seems
to be reasonable to assume that in a state of nature the parasite may oc-
casionally lay eggs on unattached ticks, yet when one considers the habit
which the nymphs have of waiting on the vegetation for rodents to pass
within reach, in many species at least, it is realized that the parasite may
have better success in finding ticks in considerable numbers by imitating
the ticks in searching for rodents or other animals.

It should be borne in mind also in further work on the biology of these
exceedingly interesting parasites, that egg laying in stages other than the
nymph may be connected in some way with special adaptations which may
be necessary in the full round of the insect's biology.

Development of the French Parasite.

The act of ovipositing appears to have little or no effect on the health
and vigor of the tick. Feeding on the host continues as usual and when fully
fed the tick drops off. In the rearing of parasites unit lots of flat nymphs
of about 250 each are used on each laboratory animal, and on an average
of about 75 fully fed nymphs are recovered from each cage bag. The feeding
of these ticks is done in wire cages enclosed in bags of unbleached muslin,
and the process is carried on in a room held at about 75 °F. This method
was devised by Doctor R. R. Parker some years ago when it was found that
a high room temperature caused the ticks to feed more successfully.

The following table is condensed from the records made in rearing ten
"Series," or generations, of parasites:

Series
No.

No.
Nymphs

Host

No.
Nymphs
Para-
sitized

No. Ticks
Produced

Per Cent
Para-

Per Cent
Producing

No.
Adult

in Series

Parasites

sitized

Parasites

Ticks

1

124

Rabbit

112

90

88.7

83.5

6

2

228

C 't 'ntail Rbt.

224

190

98.2

84.8

1

3

81

Rabbit

34

28

41.9

82.3

21

4

46

Rabbit

0

0

0

0

41

5

254

Rabbit

166

123

62.9

74.0

68

6

154

Rabbit

26

16

16.8

61.5

106

7

139

Rabbit

55

37

41.9

67.2

53

8

98

Rabbit

22

10

22.4

45.4

58

9

37

Mtn. Rat

2

0

5.4

0

28

10

128

Mtn. Rat

75

57

58.5

76.0

57

22 SEVENTH BIENNIAL REPORT

These figures show that of the total engorged nymphs recovered from
the bags an average of 48.53 per cent were parasitized, the per cent varying
from 0 per cent in Series 4, in which a domestic rabbit was used, to 98.2 per
cent in Series 2 in which a cottontail rabbit was used. The table further
shows that the percentage of the fed nymplis to produce adult parasites
varies from 0 per cent in Series 4 to 84.8 per cent in Series 2, and an average
percentage of 71.8. With more experience we have been able to raise the
percentage of parasitism, and 80 per ceut is now common.

The parasitized and non-parasitized engorged nymphs cannot be dis-
tinguished up to the time they finish feeding nor for some time thereafter.
In fact, the number of days between dropping and showing visible signs of
parasitism varies greatly. We have no data on the length of this period out
of doors but numerous rearings in which the parasitized nymphs were held
at constant temperatures in thermal cabinets have shown the following re-
sults :

At 17 °C., minimum 22 days, maximum 43 days.

At 22°C., minimum 12 days, maximum 48 days.

At 27 °C., minim urn 12 days, maximum 25 days.

At 32°C., minimum 12 days, maximum 31 days.

The highest percentage of nymphs to successfully complete their develop-
ment and produce adult parasites is at 22 °C., at the temperatures tried up to
this time. This is not very far from the most favoraljle temperature for the
parasite and an average of long series of rearings shows that the number of
days from dropping to the first indications of parasitism at this temperature
to be 18.49 days.

In the experiments summarized above we also included a parasitized lot
at 12°C. This experiment was started on July 18, 1927, and at the date of
this writing (March 1, 1928), none of the nymphs have yet yielded adult
parasites. Signs of parasitism began to show up on September 28 and exami-
nations made from time to time have shown others to show parasitism. On
January 4, 192S, additional nymphs were found to be parasitized and on this
date (March 1) the parasites are still alive and 12 more have just been "iso-
lated" as parasitized. It is doubtful whether the parasites of this series
(12°C.) will ever mature, but it is clear that there is great vitality in the
species and it is indicated that it may survive exposure to lowered tempera-
tures for a prolonged period.

At these same temperatures the minimum and maximum days from
dropping to emergence of the adult parasites are:

At 17 °C., minimum 76 days, maximum 97 days.

At 22 °C., minimum 40 days, maximum 51 days.

At 27 °C., minimum 33 days, maximum 44 days.

At 33°C., no adults emerged, the temperature being too high. Averaging
the duration periods for all of the parasites reared at 22 °C. we have 45 days,
and in our experience in rearing very many parasites at this temperature in
the practical work at the Hamilton Laboratory, we have found that we may
depend upon the bulk of the parasites to emerge in close to 45 days.

The signs of parasitism, to which reference is made above, is a very
characteristic mottling or striping shown in figure 8. Laying open the nymph
just at this stage, by fastening to a small block of paraffin and running the
very fine point of a small scalpel around the border, one finds that the ap-

STATE BOARD OF ENTOMOLOGY 23

penrance is caused by the larvae showing through the now translucent body
wall. The larvae at this time are very dark from the contents of the intes-
tinal tract, which is made up very largely of the blood which the tick had
drawn from its host. The entire contents of the tick is now within the para-
sites and the entire cavity is occupied by the larvae. The tick must have died
some time earlier, or generally in something less than 18 days at 22 °C. The
ticks are alive and able to crawl for some days after dropping, which for our
purpose is fortunate for thereby the nymphs are able to hide away when in a
state of nature and provide places more suitable for the parasites than would
be found on the bare surface of the ground. The tick is seeking a suitable
place for passing the quiescent period before emerging to the adult tick
stage but in so doing it is providing a measure of protection for the para-
sites. The adult ticks and adult parasites thus arise from the same places.

A parasitized nymph opened before the external mottling has appeared
reveals the larvae imbedded in the semifluid visceral mass from which they
may be separated if the mass is spread out. Their size naturally depends
upon their age, and the difficulty of finding them is proportional to their
size. We have as yet been able to discover almost nothing of the processes
of development and the early effect on the tick host up to the time that the
larvae may be easily seen.

Beginning at the time the larvae may be found in the wet mass of the
viscera the process, as observed, is as follows: The larvae continue to feed,
gradually reducing the body contents until it is all gone, only the empty
shell renmining. Up to this time the larvae apparently do not void anything
from tlie intestinal tracts. The body is semi-transparent, excepting the in-
testinal tract, and under a moderately high-powered binocular microscope the
brown or blackish granular intestinal contents may he plainly seen through
the body wall. During several days the shell of the dead tick contains only
the distended larvae; then the larvae commence voiding the intestinal contents
in the form of numerous dark brown pallets, each one of which is enclosed
in a clear, glistening membraneous covering. Among these are to be found
a smaller number of clear white or translucent pellets, otherwise like the dark
ones. These pellets are piled all in one place, generally, though rarely the
pile is divided. The mass of fecal pellets is most often piled in the anterior
end of the cavity. The process continues until the intestinal tracts are emp-
tied, when the larvae appear as whitish or translucent maggot-like grubs
disposed in one part of the cavity with the mass of feces in the other part.
The larvae next arrange themselves in parallel positions with their anterior
ends directed away from the pellets, in which position they pupate leaving
the pupae similarly arranged.

The size of the larvae is inversely proportional to their number in a
single tick and the size of the resulting adults correspondingly varies. It is
evident that the larvae must consume all of the semifluid mass in the host
tick in order to be successful in completing their transformation and expand-
ing their wings. Clearly there is here a very nicely adjusted adaptation and
one is impressed with the neatness of the operation. The pure white pupae
occupy one part of the cavity while the pile of fecal pellets occupies another,
and when the pupae emerge to adults there is space in which they may expand
their wings. The mass of moist pellets probably also assists in maintaining
a proper degree of humidity in the cavity. In a few rare instances we have
observed small amounts of unconsumed viscera in the cavity of the tick 's body.

24 SEVENTH BIENNIAL REPORT

Many times on opening nyinphs in which the development of the para-
sites had been delayed, we have observed the larvae to be below the average
in nnmber, though the duration of the period of development is apparently
not just inversely proportionate to the number of parasites.

The appendages of the insects, legs, wings and antennae are evident in
the naked pupae as would be expected in this group of insects. See figure 3.
While at first white, the pupae gradually darken and a reddish pigmentation
appears in the eyes and ocelli. A single emergence hole is gnawed through
the body wall and the mature insects file out and preen themselves. Mating
takes place immediately.

It is possible that the adaptation in the species whereby all of the con-
tents in the tick's body is consumed before further development proceeds will
explain why the parasite is found only in nymphal ticks. If it is a fact that
a considerable amount of the wet visceral mass left over in the tick would
be an interference in preparing a clear space in which to pupate, or would
upset the balance in the humidity, the species may have adapted itself to a
food mass just large enough to be consumed. It is quite conceivable that
the food mass in a fed larva is too small and that in a fed adult is too large.

The Number of Parasites per Tick.

Numerous counts of the number of parasites to emerge from a single
nymph have been made. It should be borne in mind that these counts have
been made only in connection with the laboratory rearing of parasites. The
number per nymph in nature may be very different. The number of para-
sites to emerge from a single tick under these conditions^ as based on 100
nymphs taken at random from routine rearings, was found to vary from 4 to
66 and averaged 21.19. The lowest number ever found was 2 and the highest
73. The size of the insects naturally varies inversely in proportion with the
number to derive their food from one tick.

Seasonal History of the Parasite.

Having as yet had no experience with I. caucurtei in nature we can ven-
ture no opinion on what the seasonal history may be. However, certain ex-
periences in the laboratory appear to have a bearing and are important.

In the Fall of 1926, soon after we obtained our initial supply of the living
parasite, we attempted to hold our stock at various lowered temperatures
hoping that it would become inactive and survive until spring when the adults
might be liberated out of doors in our experiments. We did this to conserve
our limited supply of nymphal ticks and to save labor. By December it
was found that the parasites, which were principally in the pupa stage, were
dying off rapidly. Much care had been taken to maintain the correct hu-
midity and yet the parasites were found to die if held too long at a low
temperature (12° and 17 °C.), or they would go on with their development
and emerge if held at higher temperatures. Since that time we have found
it to be more expedient to keep the parasites breeding all winter. In more
recent experiences, as reported on an earlier page, we have found that de-
velopment goes on, though slowly, at as low a temperature as 12 °C.

Up to the present time it appears that the species is primarily adapted
to continuous development throughout the year and that it has not developed
a hibernation adaptation, at least of the more usual kind. If this is true

STATE BOARD OF ENTOMOLOGY 25

it is indicated, in turn, that the insect is adapted primarily to a tropical or
sub-tropical climate in which case it was probably introduced into France in-
stead of being strictly native there.

Longevity of Adult Parasites.

Doctor Brumpt found that in captivity the life of the adult parasites
does not exceed eight days. In our work on /. caucurtei, which has been
done in considerable volume, we have frequently noticed that the adult dies at
room temperature in two to four days. On September 24, 1927, 14 parasitized
nymphs which had been held during development at 17 °C. were, upon emer-
gence, placed at 2° to 6°C. and observed for longevity from day to day.
Under these conditions the period varied from 12 to 19 days.

In an experimental liberation in Blodgett Canyon started June 28, 1927,
in which 50 tubes of parasites were attached individually to small balls of
cotton and so arranged that when disturbed by rodents the parasites would
be liberated, one vial was dropped from the cotton by the animal that dis-
turbed it and the small cotton plug failed to come out. Just two weeks after
the tube had been put out, a field man discovered the tube where it had been
dropped and found all the parasites to be alive. These parasites in a small
vial on tlie ground had survived for 14 days and might have lived longer.
This happened in a small ' ' cave ' ' in the rocks inhabited by mountain rats,
and the temperature at 11 a. m. on the day of the discovery, was determined
as 9°C. This experience plainly indicates that the life of the parasites in
a state of nature may be much longer than in the laboratory.

Correlation Between the Seasonal Histories of Dermacentor andersoni
Stiles and Ixodiphagus caucurtei duBuysson.

In an attempt to colonize the French tick parasite on the prevailing tick
of the Northwest region, a primary consideration of necessity must be a
suitable relationship between the life histories or seasonal requirements of
both species. The ticks in the proper stage or stages of development must be
available to the parasites at the egg-laying periods of the latter species.
Laboratory studies of the parasite, as already stated, have indicated that the
species is not primarily adapted to a period of hibernation in the usual sense.
Moreover, we have as yet discovered no indication that the parasite is adapted
to a period of aestivation during unsuitable temperatures for development in
the late summer months.

From the data at hand it appears that the parasite requires a continuous
supply of nymphs in which to lay eggs during the summer months and that
as cold weather comes on in the fall, the species will be required to become
inactive without a special adaptation for hibernation through a protracted
period of unfavoral)le temperatures.

Climate of Paris and of Montana.

Since /. caucurtei is known to have come from near Paris, at Fontaine-
bleau and Chantilly, where it must be more or less well adapted, although
it may have come originally from some other part of the world, it is of
interest to compare the climate of Paris with that of points in Montana.
Hamilton, Helena and Miles City are chosen for comparison. These points
are fairly representative and parasite colonies are to be established near these
points, if possible. The Board's laboratory is located at Hamilton and the
principal experiments in colonizing the parasite are located nearby, in the

26 SEVENTH BIENNIAL, REPORT

mountains. Miles City is located some 475 miles eastward, in the eastern
end of the state, well into the plains area. Helena is intermediate geograph-
ically and the climate is intermediate. The winter atmospheric temperatures
in the mountains near Hamilton are lower than at the town which is in the
Bitter Eoot Valley, but there is more snow in the mountains which has a very
marked influence on temperatures at or near the surface of the ground, where
the parasite must pass the winter. Precipitation records for the winter
months at Hamilton and ]\liles City show similarity and yet it is a fact that
more snow lies in the mountains near Hamilton than on the plains surround-
ing Miles City.

The normal climographs herewith presented are based on records obtained
through the Weather Bureau of the United States Department of Agriculture
and from "Handbuch der Klimatologie" by Julius Hann, 1911. Each climo-
graph is compiled from records covering a considerable number of years, in
no case less than twenty years.

The temperature is given in degrees Fahrenheit and the precipitation in
inches. It will be observed that Paris has the mildest winter climate while
Hamilton and Helena are intermediate and Miles City is coldest. Paris has
a higher precii)itation during the fall and winter months, while the points in
ilontana have a higher precipitation in May and June. In general, the climate
of Hamilton is more like that of Paris than is that of Helena or Miles City.

A table is presented which gives also the mean minimum temperatures
and the lowest temperature records for the points covered in the climographs.
It will be observed that the points in Montana have much lower air tempera-
tures in winter than does Paris.

Mean Minimum Temperatures Lowest Temperatures Recorded

Paris Hamilton Helena Miles City Paris Hamilton Helena Miles City

(20 yrs.)

(20 yrs.)

(42 yrs.)

(41 yrs.)

(47 yrs.)

(20 yrs.)

(42 yrs.)

(44 yrs.)

Jan.

32.4

17.5

12.1

3.4

1

-33

-42

-65

Feb.

32.7

18.9

14.5

5.3

4

-28

-41

-49

Mar.

36.3

26.9

23.0

19.6

12

-13

-20

-38

Apr.

40.5

33.6

33.4

34.7

26

8

6

- 7

May

46.2

39.4

41.0

44.1

29

18

22

17

June

52.0

46.3

48.3

53.7

36

30

31

33

July

55.4

50.4

54.1

58.9

42

36

36

31

Aug.

54.3

49.6

53.1

56.3

42

32

29

32

Sept.

50.0

42.1

44.3

45.5

33

28

20

16

Oct.

43.9

33.7

35.5

34.2

23

11

- 1

- 5

Nov.

37.4

26.8

24.3

21.2

5

- 9

-22

-26

Dec.

35.1

18.1

17.4

11.0

-14

-20

-40

-52

Extent of the Problem in Montana.

The wood tick is found more or less scatteringly throughout the greater
part of Montana and cases of Rocky Mountain Spotted Fever have occurred
in 32 out of a total of 57 counties, though in most of these counties the
disease exists only in the milder form. It is desirable then that parasites
may destroy the ticks throughout the State.

The State of Montana is as large as an empire, being the third largest
of all the states. It is 560 by 310 miles in extreme limits. Within this are
found numerous types of country with widely varying physical features, in-
cluding rugged mountains, foothills and plains. Ticks are to be found in the
most inaccessible mountain fastnesses, the mountain valleys and basins, the
agricultural valleys and grazing lands, and in the plains country which is used
for stock raising, or in some cases, left unused. If once started, ticks can find
more or less favorable conditions wherever rodents occur as hosts of the early
stages, and large animals, whether wild or domestic, as hosts of the adult ticks.

STATE BOARD OP ENTOMOLOGY

27

28 SEVENTH BIENNIAL REPORT

The problem of the use of parasites as destroyers of ticks is therefore a
large oae and moreover, the results of our study and experiments are applicable
also in the states of the northwest and in Canada.

Description of Plates.
Plate 1.

Fig. 1. Adult parasites that came out of one tick, and the killed tick. (Magni-
fied about 6 times.)

Fig. 2. Adult parasites magnified about twelve times. The variation in the
size of the parasites is well shown.

Fig. 3. Pupae about ready to emerge as dissected from a killed tick. Magni-
fied about twelve times.

Plate 2.

Fig. 4. Two dead nymphal ticks cut open to show the parasites in a natural

position. The one at the left shows the fecal pellets at the lower

end. The pupae at this stage are pure white.
Fig. 5. Nymphal tick cut open and showing the entire body cavity of the

tick occupied by the larvae of the parasite. The viscera of the tick

have been completely cousuuxed.
Fig. 6. Eggs- of the parasite as they appear when removed from the ovaries

of the adult female.

Plate 3.

Fig. 7. The larval parasites removed from one killed tick.
Fig. 8. Nymphal ticks showing "signs of parasitism." The mottling is due
to the parasite larvae showing through the thin body wall of the

tick. This stage soon passes after which the killed nymphal tick is

brown in color.

STATE BOARD OF ENTOMOLOGY

29

%v *

* «. 1 %

■^% ^ %

HH v.«<<» 1'^. v^-

.^ ^ ^"^ ^

30

SEVENTH BIENNIAL REPORT

STATE BOARD OF ENTOMOLOGY 31

7

32 SEVENTH BIENNIAL REPORT

QUANTITY PRODUCTION OF TICK PARASITES

By
Fred A. Morton, Laboratory Assistant, Montana State Board of Entomology.

The Montana State Board of Entomology, in its laboratory at Hamilton,
Montana, is rearing large numbers of the French tick parasite (Ixodiphagus
caucurtei du Buysson) for liberation throughout the state. It is a Chalcidoid
parasite (sub-family Encyrtinae) which attacks nothing but ticks, and so far
as is known, develo];)s in only the nymphal stage of ticks. Consequently, rear-
ing the parasite necessitates rearing a suitable tick to the nymphal stage, and
parasite production is naturally limited by nymphal tick production.

Technique of Tick Rearing.

In this laboratory the Spotted Fever tick, Dermacentor andersoni, is
reared as a host for the parasite and since that requires rearing the tick
through all stages of its development before parasites can be produced, the
technique of tick rearing will be considered first, under the following headings :
(1) The Adult Stage, (2) The Egg Stage, (3) The Larval Stage, and
(4) The Nymphal Stage.
1. THE ADULT STAGE.

(a) Pre-engorgement Period. The flat adults are quite susceptible to
both excessive and insufficient humidity, but may be kept for about a year
with comparatively low mortality if jjla^ed under satisfactory conditions. The
method now in use is to place the ticks inside a ' ' longevity tube, ' ' which is
a pyrex tube (1^/^ in. by 8 in.) plugged with clay at one end for a distance
of about 2 in., a piece of muslin being tied over the other end. A fcAV pieces
of dried leaves or shavings are placed inside the tube so the ticks will not be
forced into direct contact with the wet clay plug. The tube is then placed in a
5 in. vertical hole in the tick yard, which keeps the clay plug in the tube
always moist, and allows the ticks to seek the humidity within the tube which
is most satisfactory to them.

Usually, after the ticks have been held in the longevity tube for 3 or 4
months, they will be found ready to feed but sometimes it is necessary to
incubate them. In this event they are placed at a high temperature
(30°-85° C.) for several days, and then at a lower temperature (15° C. or cold-
er) for a day. After several such alternations of temperature the ticks will
generally engorge quite rapidly. This type of incubation is nearly always re-
quired for ticks less than 2 months old.

(b) Method of Engorgement. For a period of several months in the
spring of the year, it is possible to purchase engorged female ticks from stock
owners wlio reside in localities where ticks are not known to be carriers of
human disease. These ticks lay eggs quicker than those engorged in the laljora-
tory, but they lay fewer eggs, probably because the laljoratory stock can be
engorged to a larger size. However, it is not safe to depend on being able to
purchase engorged ticks, and it is necessary to feed a considerable number of
adult ticks in the laboratory.

Eabbits are used as host animals in engorging adults. The rabbit 's belly
is clipped closely and two screen capsules are fitted to it by means of adhesive
tape. The capsules are circular, about 3 inches in diameter, and are stamped

STATE BOARD OF ENTOMOLOGY 33

from 20 mesh brass seieening by a die, iu such a fashion that the finished
capsule has a circular depression % inch by 2 inches, surrounded by a i/^-iuch
rim, somewhat the shape of a low crowned hat. The rim fits tightly against
the rabbit's belly and the ticks are fed within the depression. About 40 flat
ticks are put into each capsule, approximately half of which will be females.
(c) Post-engorgement Period. After the ticks have fed for 10 days the
capsules are removed from the rabbit's belly and the ticks picked. Using the
two capsules we get an average of between 25 and 30 engorged females per
rabbit. Each female is placed in a shell vial (14 inch by 1 inch) which is then
plugged with cotton and held in a humid thermal cabinet at 20° C, pending
oviposition, which, at this temperature, occurs within 1 or 2 weeks. This time
may be lengthened or shortened without injury to the tick, by using any
desired temperature between 12° and 30° C. Greater extremes of temperature
miglit not prove harmful, l)ut they have not been used.

2. THE ECxG STAGE.

The average engorged female tick lays between 5,000 and 10,000 eggs and
at 20° C. has an oviposition period of about 3 weeks. The first eggs hatch
when they are about a month old and the female dies soon after. Maintenance
of the proper humidity is quite important with eggs^ although a certain per-
cent of them remain viable under considerable desiccation.

3. THE LAEVAL STAGE.

(a) Pre-engorgement Period. The vials of eggs are examined every
three or four days and those in which the eggs have started to hatch are
transf<^rred to another tray and a record kept of the date on which the larvae,
or seed ticks, were noticed. They may be fed from two to six week's later, but
if only two weeks old, it is preferable to incubate them for several days at
30° C. prior to engorgement. Seed ticks are more susceptible to the lack of
humidity than any other stage of the tick and will die within a few days if
subjected to ordinary room humidity at room temperature. With a high
humidity they will survive at 30° C. for a month or more.

(b) Method of Engorgement. Rabliits are used as hosts for seed ticks
and are infested in the following manner: The rabbit is placed within a
32 inch by 15-inch muslin "infesting" bag suspended by hooks, and the flat
seeds from two or three vials deposited in his ears, the favorite site of attach-
ment. This is easily accomplished by tapping the vial with a small block of
wood; the seeds cling to each other and the vial may be easily emptied, as
the mass will come out almost as a unit. A piece of tape is then placed
around the rabbit 's ears to prevent his shaking the seeds out lief ore they be-
come attached; the liag is tied with a piece of string and then placed iu a
cage. The cage rests in a frame, around which another bag is tied. The tape
is removed from the rabbit's ear 24 hours later and the infesting bag removed
and burned. On the third or fourth day some of the seeds, having become
completely engorged, detach themselves from the rabbit 's ears and drop to the
bottom of the bag surrounding the cage. Just before the seeds start dropping
the bags are cleaned out, and they are picked by turning the bags inside out
within a galvanized sheet metal container 27 inches square by 6 feet high, and
shaken clean. A 14-mesh removable screen inside this device separates the
engorged seeds from the trash, and the seeds roll down the funnel shaped
bottom into a removable cup which has a screen, with meshes just sufficient
to retain the seeds, soldered across the lower end. After all the bags are thus

34 SEVENTH BIENNIAL REPORT

picked, the cup is removed and shaken to clean the seeds of small debris. It
is necessary to pick these bags of seeds twice, either on the third and fifth
or the fourth and sixth days. We obtain approximately 3,000 engorged seeds
per rabbit.

(c) Post-Engorgement Period. After picking, the seeds are measured in
eul)ic centimeters and poured into longevity tubes, 12 or 15 ce. to the tube.
These tubes are kept for about three weeks at room temperature with their
clay plugs resting on moist sand. At the end of this time most of the seeds
have molted to nymphs and may be transferred out doors to the tick yard.
4. THE NYMPHAL STAGE.

(a) Pro-engorgement Period. The flat nymphs are kept in longevity
tubes for periods ranging from two to eight or nine months. They have been
found to overwinter Ijetter out doors than when kept inside, although the
mortality is quite high in either case, a 30% mortality being considered average
when kept out doors. Nymphs present an added difficulty when it is desired
to engorge them; they frequently refuse to feed even when several months old,
and thoy are extremely resistant to known methods of incubation. The present
system is to place the nymphs (which are at least six weeks old) at 30° C. for
two or three days, and then at 6° C. for a day. This procedure is repeated
until a fair number of them crawl up on to the cloth which is tied over the end
of the tube. An average of about 15% of these will feed, while practically
none of those will feed which remain in the trash at the bottom of the tube.

(b) Method of Engorgement. A longevity tube is selected which has a
suitable number of active flat nymphs on the cloth. The cloth is removed and
the nymphs on it smeared in the ears and around the eyes of a rabbit in an
infesting l)ag. The rabbit is then treated as described under "Method of
Engorgement of Seeds," and the engorged nymphs are picked in the same
device as was used for the seeds, using, of course, a screen of larger mesh.
Nymphs are picked on the fourth and sixth, or fifth and seventh days.

(c) Post-engorgement Period. The nymphs are measured in cubic centi-
meters and then put in cardboard pill Ijoxes, about 50 nymphs to the box. In
about a month they start molting to adults, and just prior to molting are
transferred to longevity tubes, about 400 to the tube. They complete molting
in the tubes and are then put out in the tick yard.

Technique of Parasite Rearing.

When parasites are to be reared the ticks are reared to the nymphal stage
as already described, and are then parasitized by the following method:

From 12 to 24 hours after the rabbit has l)een infested with flat nymphs,
50 to 100 parasites are shaken into the rabbit's ears and around the head, and
he is tied up in the infesting bag for 4 or 5 hours longer. The parasites im-
mediatel}' attack and lay eggs in the engorging nymphs.

These parasitized nymphs engorge, drop, and are picked exactly as normal
nymphs and after being put in pill boxes are placed at 22° C. Three or four
weeks later the parasitized nymphs may be easily distinguished from the others
by the fact that the parasitized ones have turned l)rown, while the normal ones
retain their blue color. The normal nymphs are allowed to molt to adults, and
are placed in the tick yard with the other flat adults, while the parasitized
nymphs are removed and the majority of them sent to locations throughout
the state where it is desired to establish the parasite. A few are retained to

STATE BOARD OF ENTOMOLOGY 35

keej) a foiitiuuai siii)])ly (ui liaiul for jjarasitization, and these are placed indi-
vidually Nvithin a 2-intdi piece of 6-millinieter glass tubing, cotton jdugged at
both ends. These are then placed at any desired temperature between 18°
and 23° C, which are loiown to be safe limits. The tubes are looked over
daily, and those containing adult parasites are either used immediately or
placed at (5° C, where they may be kept with low mortality for about a week.
We obtain an average of 20 parasites per nymph, and a 70% parasitiza-
tion. Parasites emerge from approximately 80% of the parasitized nymphs
under conditions of fairly high humidity, Init are unable to emerge if the
nymphal shell l)ecomes dry and ])rittle.

TICK PARASITE LIBERATION IN MONTANA DURING 1928.

J. R. Parker, Acting State Entomologist, and
W. J. Butler, State Veterinary Surgeon

The fight on parasites is universal ; no country is free from them. Some
are of lesser, others are of greater importance. Some are agricultural pests,
others attack man and animals. Naturally, those parasites which are the most
insidious and hardest to control have an intricate and complex life cycle. In
such cases, control by medicinal or mechanical agencies is very difficult and
ineffective. New methods continually have to be devised. Today, one of the
most advanced methods of fighting and controlling many of our parasites is
Avith parasites.

The Montana Slate Board of Entomology is commissioned with the duty
of investigating and studying the dissemination by insects of diseases among
persons and animals, with the purpose of eradicating and preventing such
diseases. Thus far the study of the Board has been confined largely to the
tick, Dermacentor andemoni, which is known to be a carrier of the causative
agents of Spotted Fes'er, Tick Paralysis and Tularaemia.

The Montana State Board of Entomology has naturally been greatly
interested in the tick parasite studies of Doctor Brumpt, Professor of Para-
sitologv at the University of Paris, and particularly in the efforts of Doctor
Brumpt 's associate. Doctor Larrousse, to introduce the French tick parasite
(Ixodiphagus caucurtei du Buysson) into the United States. In 1926 through
the efforts of Doctor S. B. Wolbach, of the Harvard Medical School, Doctor
Larrousse came to the United States and established a tick parasite colony
on Naushon Island. Professor R. A. Cooley, representing the Montana State
Board of Entomology, proceeded to Naushon Island and there reviewed and
studied with Doctor Larrousse the methods used in rearing the tick parasite
/. caucurtei. Through the courtesy of Doctor Larrousse, Professor Cooley
obtained and brought to Montana 27 of these parasitized nymphs. This small
initial stock has gradually been increased to the extent that during the summer
of 1928 we were able to release 381,190 parasites and still hold enough in
reserve to provide a much larger supply of parasites in 1929.

The tick parasite and its habits are described in considerable detail by
Professor Cooley elsewhere in this report. It is sufficient to say at this time
that it is a tiny wasp-like insect about 1/16 of an inch in length. The nmture
parasite does not sting or bite and is harmless to man and beast. The adult
female's only concern is to lay eggs in the nymphal stage of the tick while
the male's whole sphere in life is to fertilize the female's eggs.

36 SEVENTH BIEXNIAL REPORT

Wlien matured i^arasites are liberated they seek rodents and other small
animal life that harbor the nyniphal stage of D. andersoni. They then skirmish
through the hair, or fur, of the animal in search of nymphs. Upon finding
one, the ovipositor is inserted almost immediately and in most instances 5 to
10 egg:? are laid. The act of ovipositing takes but a few seconds. The female
parasite may repeat ovipositing in the same nymph, but ordinarily goes in
search of another victim. Two parasites have also been observed ovipositing
in one nymph at the same time, and it is not uncommon for more than one
female to lay eggs in one nymph.

Mr. Kohls, at the Board of Entomology La)ioratory in Hamilton, reports
having observed one female parasite insert its ovipositor in one nymph 47
times. The eggs of the parasite hatch into tiny maggots which feed upon the
tissues uf the nyniphal tick finally killing it. After the maggots or larvae are
full grown they transform to pupae within the body of the tick where they
remain until they emerge as adult parasites.

In distributing the tick parasite and in the endeavor to establish tick para-
site colonies, the two methods most commonly used are as follows :

Ticks for the rearing of the parasite are gathered in districts where
Spotted Fever, Tularaemia or Tick Paralysis have never been known to occur.
Nymphs from these ticks are used for the breeding of parasites.

Parasitized nymplis are placed in glass vials open at both ends. Over the
open ends wire gauze is attached. The mesh in the wire gauze is large enough
to permit the escape of the parasites when they emerge from the nymphs. The
wire gauze is simply an added precaution to prevent the loss of the nymphs,
or their escape should one happen to l:ie not parasitized and remain alive. These
glass vials containing tlie parasitized nymphs are taken out into the country
and placed at tlie mouth of rabbit holes, mice and rat runs and in and around
the nests and holes of other rodents that harbor the nymphal stage of
D. andersoni. Nymphs are not found on the common domestic animals. In
some cases and especially in a pack or mountain rat country, cotton and
bright articles are attached to the glass vials so as to attract the pack rats and
have them carry the vials to their nests.

The second method is to trap rodents, take them to the lalH)ratory and
allow new'ly parasitized nymphal ticks to attach themselves to the rodent. The
latter are then returned to the locality where they were caught and set free.
After the nymphal ticks have completed feeding they drop from the rodents,
crawl to protected places in trash or in rodent burrows. In such places condi-
tions are ideal for the development of the parasites and when the adult para-
sites emerge they generally will have little trouble in finding tick infested
rodents close at hand.

Areas in which tick parasites (/. caucurtei) were to be liberated were
selected on the basis of previous distril)ution of Rocky Mountain Spotted Fever
in Montana, with the end in view of establishing colonies of parasites in those
areas where the disease had l)een most abundant. The selection of points within
these areas at which the actual liberation of parasites was to take place was
based on the abundance of adult ticks and various small rodents which act as
hosts for nymphal ticks. In the selection of liberation points in Eastern
Montana, Doctor R. R. Parker of the U. S. Public Health Service, who had
formerly spent two years studying ticks in that section of the state, accom-
panied the State Board workers in their searcli for localities most suitable for

STATE BOARD OF ENTOMOLOGY 37

the development of the parasite. His knowledge of Eastern Montana condi-
tions saved many days of travel and gave assurance that the most desirable
places were selected. Doctor Baldwin of Miles City and Doctor Smith of
Billings, representatives for the Livestock Sanitary Board, aided the tick para-
site work in every possible way. Their knowledge of local tick aljundance was
most helpful and they stood ready at all times to either transport the State
Board workers or to receive and release shipments of tick parasites from the
Hamilton Laboratory'.

In the laboratory the uuml)er of parasites emerging from one nymphal
tick varies from 2 to 73, the average of 100 nymphs taken at random in one
experiment being 2^. In estimating the number of parasites liberated we have
thought it better to be conservative and have taken 14 as the average number
of adult parasites emerging from each parasitized engorged nymphal tick.
Localities, dates of liberation and the estimated number of parasites released
are shown in the following table:

Tick Parasite Liberation During 1928.

Bitter Root Valley
Place Dates and Number of Parasites Released Total

Lake Como May 24, 250 : June 7, 4,920 ; June 22, 1,600 ; July 9,

2,400; Oct. 6, 30,000 39,170

Blodgett Canyon May 22. 250 ; May 29, 2.680 ; July 10, 7,200 : Oct. 30,

20,000 30.130

Lo Lo Canyon Oct. 6, 30,000 30,000

Lick Creek June 22, 2,400; July 13, 4,800; Oct. 18, 75,000 82.200

O'Brien Creek June 15, 4,000 ; June 29, 4,800 ; July 13. 9,600 ;

Oct. 6, 30,000 48,400

Total 229,900

Central and Eastern Montana

Helena April 30, 1,400 ; June 5, 700 ; Oct. 3, 15,000 17,100

Bozeman June 2, 1,120; June 9, 700; Oct. 2, 14,000;

Oct. 15, 7,000 22,820

Edgar April 22, 336 ; May 9, 840 : May 21, 280 ; July 16,

644 ; Aug. 20, 700 ; Sept. 23, 20,000 22,800

Musselshell May 7, 420 ; May 22, 280 ; June 15, 2,000 ; July 4,

2,000 ; July 15, 644 ; Aug. 15, 560 ; Aug. 20, 700 ;

Sept. 26, 40,000 46,600

Forsyth May 8, 210 ; May 23, 280 ; July 16, 644 ; Aug. 20, 700 ;

Sept. 24, 15,000 16,830

Miles City April 21, 336 ; May 8, 420 ; May 23, 140 ; June 1, 700 ;

June 16, 3,500; July 15, 644; Aug. 24, 700;

Sept. 25, 18,000 24,440

Garfield County June 2, 700 700

Total 151,290

Grand total for season 381,190

With reference to overwintering, it is pleasing to report that Mr. Fred
Morton, supervising parasite rearing work for the Board of Entomology at
the Hamilton Laboratory, has advised the Board that he has recovered para-
sites from the Mill Creek hibernation experiment. The data in this experiment
are as follows:

Twentj'-eight nymphs dropped September 20, 1927, and 20 dropped iSep-
tember 23, 1927, were placed in two longevity tuljes containing a few leaves
and pine needles. They were still active and were held at 19° C, prior to
being placed out doors on October 1, 1927. These tubes were placed on the
ground and both ends covered with leaves. These tubes were Ijrought into
the laboratory on April 11, 1928. They were held at room temperature, and
on May 23, 1928, matured parasites emerged from three of these nymphs.
In this particular experiment parasites under out door conditions carried
over the winter.

38 SEVKXTH BIEXXIAL RFJPORT

It is also c'ucouiiiging aud pleasing to note that Doctors Larrousse, Wol-
bach and King report that I. caucurtei survived the winter under natural
conditions and were able to reproduce on Naushon Island. (Science LXVII,
No. 1735.)

Professor Cooley, representing the Montana State Board of Entomology,
but financed by private subscriptions, is now in Africa in an endeavor to
secure other parasites for D. andersoni, and also to secure additional data
on the present known parasites which may aid the Board in its work of eradi-
cating, or at least controlling, in our most infested districts, the tick
D. andersovi.

The work so far has been encouraging. With added experience which will
come as the work progresses, together with the adequate laboratory facilities,
which the State of Montana has so generously furnished, and with the data
and parasites which Professor Cooley may bring homo, we are justified in
the hope that we may so reduce the tick population by the use of parasites
as to make Spotted Fever, Tick Paralysis and Tularaemia rare diseases in
the State of Montana.

STATE BOARD OF ENTOMOLOGY 39

ROCKY MOUNTAIN SPOTTED FEVER

ROCKY MOUNTAIN SPOTTED FEVER H)

By

E. R. Parker, Special Expert, United States Fuhlic Health Service

Rocky Mountaiu spotted fever was recognized as a distinct disease entity
by many of the early physicians of the Rocky Mountain region for many years
before any attempt was made to determine either its etiology or mode of
transmission. Since the first studies by Wilson and Chowning (1902-1904)
there have been many field and laboratory investigations relating to epidemio-
logical, etiological, serological, immunological and entomological phases. The
most important of these, because of their fundamental significance, were :
First, those of Ricketts and his associates of the University of Chicago
(1906-1909), who showed that the disease is primarily an infection of small
mammals among which it is transmitted by the wood tick (Dennacentor under -
soni Stiles) and that large mammals are not susceptible, who proved to be
fact the wood tick theory of human infection advanced by Wilson and Chown-
ing and who made important observations and deductions concerning the main-
tenance and behavior of the virus in nature; second, the entomological and
zoological studies by Prof. R. A. Cooley, State Entomologist of Montana, in
association with Hunter, Bishopp and King of the federal Bureau of En-
tomology and representatives of the Bureau of the Biological Survey
(1909-1911), which resulted in demonstrating the two-year life cycle of the
wood-tick — larva, nymph and adult engorging in successive years — and the
relative importance of many mammals as tick hosts ; and third, those of Dr.
S. B. Wolbach of Harvard Medical School (1916-1919), who showed the
rickettsial nature of the virus.

The most comprehensive investigation of Rocky Mountain spotted fever,
however, was begun by the Bureau of the Public Health Service in the fall of
1921 under the direction of Surgeon R. R. Spencer, with whom the writer has
since been associated. This investigation has been carried ou in co-operation
with the Montana State Board of Entomology, which was created in 1913 for
the specific purpose of dealing with the spotted fever problem in Montana.
To the fiersistence of this Board'2) (the membership has fortunately remained
intact since its organization) under often discouraging conditions, is due much
of the progress that has been made.

Despite these various investigations, however, and the resultant continued
additions to our knowledge there are still many unsolved and puzzling problems

(1) This paper was read before the Section on Medical and Veterinary Entomol-
ogy of the Fourtli International Entomological Congress at Ithaca. X. Y.,
August 13. 1928.

(2) Professor R. A. Cooley. State Entomologist. Secretary; Dr. W. P. Cogswell,
Secretary of tlie State Board of Healtli, chairman; Dr. W. J. Butler. State
Veterinary Surgeon, member.

40 SEVENTH BIEXXIAL REPORT

relating to etiology, local variations in the virulence of the virus and its main-
tenance and spread in nature, and the incidence, distribution and prevention
of human cases.

In this paper it is the purpose of the writer to discuss tliese general
phases, particularly from the standpoint of the data secured by Surgeon E. E.
Spencer and himself, in the hope that he may convey a reasonably compre-
hensive general conception of the present status of the problem. This has
seemed desirable not only because no paper relating to spotted fever has been
read before an entomological meeting for nearly ten years (never one of a
general nature), but also in deference to our visitors from other lands to
wliora the subject^ which is one of our outstanding problems in medical en-
tomology, is less familiar than to ourselves.

Maintenance and Perpetuation of Rocky Mountain Spotted Fever
Virus in Nature.

In 1909, after four years of investigation, Eicketts supposing a one year
life cycle of the Avood tick, conceived that the virus of Eocky Mountain
spotted fever was maintained in nature in the following manner: The virus
was carried over the winter in infected female ticks, from about fifty per cent
of which infection was passed on through the egg to the resultant larvae. The
latter were able to infect susceptible rodents upon which they chanced to
engorge, the virus being then picked up by non-infected immature ticks that
were infesting such rodents, and by stage to stage transmission, which he
had shown to occur, was passed on to adults of that generation. The process
repeated in each generation, resulted in perpetuation. He felt that if de-
pendent on hereditary transmission alone, which at first thought Avould seem
sufficient, it would gradually die out.

Except for slight modifications to fit the later-proven two year life cycle
of the wood tick, subsequent investigations in the main have verified Eickett 's
findings and ideas, but have also extended them and have introduced into the
problem of maintenance a new factor, the transmission of the virus by the
rabbit tick, Haemaphysalis leporis-palustris Packard, which was demon-
strated by Parker in 1921. This tick infests all species of rabbits and
is common on game birds. It was first suspected as the result of two years'
observations (1916-1917) of ecological relationships in spotted fever main-
tenance in Eastern Montana. These studies suggested that wood tick trans-
mission alone was insufficient to account for the survival of the virus over
periods of several years, common in some sections of eastern Montana, during
which wood ticks become very scarce. The evidence at hand indicated the rab-
bit tick as the most logical parasite to be studied as a possible second carrier.
Whether or not the premise were well taken, studies made in the Bitter Eoot
in 1921, several years later, resulted in showing that this tick is a vector and
that infected individuals could be recovered in nature. Our later observations
have shown that stage to stage and hereditary transmission of the virus occur
in the same manner as in the wood tick.

Evidence thus far secured, therefore, points to stage to stage transmission
of the virus within each successive generation of the tick carriers, its heredi-

STATE BOARD OF ENTOMOLOGY 41

tury transmission from one generation to the next, and the starting in each
generation of new lines of tick infection each year through the medium of
tick-infested small man)mals, as the three apparent channels along -which in-
fection flows to achieve perpetuation. In the light of present knowledge in
any given focus of infection the successful flow of the virus along these
channels is dependent upon factors of several orders; each separate factor
being a variable both from year to year and focus to focus.

The factors of the first order are: Tick abundance, and those which
affect the survival and virulence of the virus in ticks. Otf the latter, except
that they exist, we must confess almost complete ignorance. Presumably,
however, they may be meteorological, they may have to do with the kind of
animal blood ingested or even with the idiosyncrasies of individual ticks, or
conceivably all three may be concerned. Of tick abundance we can speak with
more confidence. Provided conditions are favorable for the survival of
virus in the ticks, it is the element of chance that controls the flow of infec-
tion along the channels indicated, and the likelihood that continuity will be
maintained obviously increases or decreases as ticks increase or decrease in
abundance.

Whether ticks increase or decrease, that is, relative tick abundance, is
controlled by factors of the second order which resolve into two groups:
(1) meteorological, (2) those which concern host availability. Of the first
group we again confess a far from satisfactory knowledge, but we do know
that the activity and survival of ticks is unfavorably affected by extreme
dryness or moisture, and by abrupt or continued ch.anges of temperature.
The latter group of factors consists of the abundance, actual or relative, the
habits and the distribution of each separate species of larval, nymphal and
adult tick host, whether or not that species is susceptible to infection.

The species of host animals present, their abundance and distribution, and
even their habits, are in their turn predetermined by a third order of factors
which are: Floral associations and their distribution, the local topography,
meteorological conditions again, and the character and degree of development
of local agriculture. These factors interweave to form a tangled skein which
may appropriately be called "the si^otted fever complex". As entomologists
trained to realize the importance of detail, we can readily appreciate that the
untangling of this complex so that each separate factor may be given its proper
relative value in maintaining infection, is both desirable and essential from
the standpoint of intelligently directed and successful control. This is a
problem in ecology — epidemiology, if you prefer — but as applied to any
disease complex the writer conceives the two terms as synonymous.

An investigation of this complex was begun by the writer in 1921 when
with the ^Montana State Board of Entomology. The demonstration of rabbit
tick transmission was the chief accomplishment of that season. The same line
of work was continued on a far more comprehensive scale after the entry
of the Public Health Service into the investigative field that fall; the general
plan of study involving the keeping, for a period of years, for a circumscribed
area, of as accurate and detailed a yearly record as possible of the varia-
tions of all the known and likely factors of maintenance for correlation with
annual case incidence and the yearly prevalence of virus-containing ticks.
After two years it was necessary to discontinue this line of effort in order to
concentrate on the virus investigations which later led to the production of a

42 SEVENTH BIENNIAL REPORT

^acc•me. Although the main purpose of the investigation was thei-eby pre-
vented, much new, interesting and valuable information was secured. This
concerned new host relationships; tick habits that aid them in securing hosts;
animal habits, daily and seasonal, that determine their importance as tick
hosts and explain how they function in spreading and maintaining the virus;
the distribution and prevalence of virus-containing ticks; variations in the
percentage of ticks containing virus; the functioning of the rabbit tick in
the spotted fever complex; a more accurate method than feeding alone of
testing ticks for presence of spotted fever virus and the occurrence in ticks
of an immunizing phase of the virus and the phenomenon of ." reactivation. "

This information has resulted in a much broader conception of the
spotted fever problem and a better, though far fro'm complete, understanding
of ecological relationships in the natural maintenance of spotted fever virus
both in the Bitter Eoot region and in other localities. Lack of time, however,
forbids presentation of these results except for a brief discussion concerning
the rabbit tick and the incidental working in of certain other findings in other
sections of the paper.

Incidental to the abo^•e studies was the discovery of tularaemia infected
wood ticks in nature and the subsequent proof that both wood ticks and
rabbit ticks are natural carriers of Bacterium iularense, and that the former
lick is an important agent of human infection.

There are three possibilities which may be concerned in maintenance that
have not thus far been mentioned. One is that of the existence of chronic
infection in one or more species of susceptible tick hosts, which would likely
result in a longer period during which infection could be acquired by ticks.
Little work aloug this line has been done and thus far the evidence is nega-
tive. The second is the chance that infected male ticks may transmit the
virus to females during the act of copulation. That this is a definite possi-
bility is indicated by Wolbach's finding of spotted fever rickettsia in sper-
n.atozoa. If it occurs, then hereditary transmission may be a more important
consideration in maintenance than heretofore supposed. The third is the pos-
sibility that other parasites, besides the two ticks that have been studied, may
be carriers of the virus. Very few observations have been made in this con-
nection. Eicketts showed transmission by adult Dermacentor albipictus Pack-
ard's) infected as nymphs, and Maver, transmission by nymphal D. variabilis
Say, infected as larva and by adult D. parumupertus marginatus Banks in-
fected as nymphs. No infective albipictus have been recovered from nature
in spite of repeated tests. The few tests that have been made with variabilis
have also proven negative, but this tick nuist l)e viewed with suspicion as
a possible potential carrier, since the present western limit of its range over-
laps the easternmost occurrence of D. andersoni. Parumapertus marginatus
occurs throughout the southern portion of the range of andersoni and must
be considered as a possible factor in maintenance in that section of the Rocky
Mountains.

The Rabbit Tick in Relation to Spotted Fever.

The full significance of rabbit tick transmission of the virus in the spotted
fever complex is not yet apparent. Thus far, it has been studied only under
Bitter Root Valley conditions, and incidentally rather than intensively. The

<3) These ticks were collected from horses during the winter months and Rick-
etts at the time supposed them to be D. andersoni.

STATE BOARD OF ENTOMOLOGY 43

data there secured, however, suggest that it is a factor in the maintenance of
the virus, as already noted; that it phiys an important part in the intensive
distribution of the virus in nature; and that, indirectly, it is of consequence
in human infection by increasing the number of virus-containing wood ticks.
The more important findings concerning this tick are as follows :

(1) Eabbit tick infestation of its hosts is often very heavy, the habitat
adaptations of each host species determining the degree to which it is in-
fested. Cottontail and snowshoe rabbits are especially heavy carriers. In
some seasons one hundred per cent of snowshoe rabbits examined have been
found infested; and seasonal averages may show as high as several hundred
ticks per animal examined. The percentage of grouse infested has varied from
eighteen to seventy-five, depending on the species and year. They are less
heavily infested than rabbits, but it is not uncommon to find from twenty-five
to fifty or more ticks on a single bird.

(2) Eelatively high percentages of infested hosts have been found car-
rying infected ticks. In 1922, of infested snowshoes it was 36.84; of cotton-
tails, 27.27 ; and of jackrabbits, 33.33. The percentage of grouse has varied
l)etween twenty and fifty.

(3) Heavy tick infestation and high percentages of infested hosts car-
rying infected ticks, in conjunction with the daily and seasonal habits of
movement of both rabbits and grouse, make the rabbit tick an important
medium for intensive distribution of spotted fever virus.

(4) Eabbits, of all species thus far studied, are hosts of both wood ticks
and rabbit ticks. The resultant potential opportunity for wood ticks to
acquire infection is apparently greater than for any other species of wood
tick host.

(.5) A higher percentage of virus-containing wood ticks has been found
in unfed adults collected in rabbit habitats and in animal habitats in which
rabbits are associated with other small mammals, than from those habitats
from which rabbits are absent. In 1922, of such ticks from Columbian ground
squirrel habitats, 1.05 per cent contained spotted fever virus; 1.48 per cent
from habitats in which ground squirrels and cottontails were associated; 2.40
per cent from cottontail habitats, and 5.20 per cent from ground squirrel-
snowshoe rabbit habitats.

(6) Perhaps the most interesting fact concerning this tick is that, as
recovered from nature, it commonly carries, in contradistinction to the wood
tick, a mild strain of spotted fever virus, so mild indeed that it seldom pro-
duces typical or even recognizable lesions in experimental animals. Fever is
often absent, or if present, low and irregular, and diagnosis must usually be
leased on the outcome of a subsequent immunity test with the active virus.
The reason why this tick carries a mild strain in nature is not at all clear.
When infected Avith lalxiratory strains, the virus content more often produces
characteristic infection.

An interesting and seemingly important subject for investigation is
whether wood tick infection or rabbit tick infection is the more fundamental.
This involves such questions as: Whether or not the presence of infection in
any given locality is dependent upon primary infection in the wood tick, or
iii the rabbit tick? Or, can each species maintain infection independently of
the other? If the rabbit tick were the original vector of the virus and the
wood tick secondary, then since the rabbit tick has by far the wider distribu-

44 SEVENTH BIENNIAL REPORT

tion, we would expect to be able to recover infection from this tick at points
well beyond the range of the wood tick. No attempt to do this has thus far
been made. The limits of the present endemic area, as delimited by geograph-
ical distribution of human cases, is well within the range of the last species.
The fact that both wood ticks and rabbit ticks are natural vectors of
spotted fever virus sets aside the often made assertion that each species of
rickettsia is specific for one species of insect or arachnid host.

Distribution and Spread.

Kocky Mountain spotted fever occurs in parts of the states of Washing-
ton, Oregon, California, Nevada, Utah, Idaho, Montana, Wyoming, Colorado,
and North and South Dakota. Eeports of occurrence in Arizona, New Mexico
and British Columbia have never been definitely verified. The total area in-
volved is perhaps one-eighth of the continental United States. Sporadic cases
hfive Ijeen reported from points far from the Eocky Mountain region and far
beyond the known range of Dermacentor andersoni. Most of these, however,
have occurred either in jjersons who have been recently exposed in, or who
have had oppoitunity for contact with tick infested domestic animals recently
shipped from, a known endemic area. Of the few that cannot be thus ac-
counted for the only one concerning which there has been any really sugges-
tive evidence was reported in Indiana in 1924. The serum of this patient,
after recovery, when mixed with virus and injected into guinea pigs, con-
ferred a degree of protection fully as good as the sera of many recovered
definite spotted fever cases. The possibility of making a diagnosis of Rocky
Mountain spotted fever that is incorrect in areas far from the known endemic
region is well illustrated by a case seen by Spencer in Norfolk, Virginia, in
3925. Clinically this could have been either spotted fever or typhus but the
results of Ijlood injection into guinea pigs and of other laljoratory tests were
entirely negative for both, and its etiology still remains a mystery.

The shaded parts of the accompanying map show the counties witliin the
known endemic region in which infection had been reported up to July 1, 1928.
The lighter shading indicates those counties, seventy-eight in number, in which
infection is known to have been present prior to 1914; the heavier shading
shows an additional ninety-three counties in which infection has since been
reported. To what extent it shows recent better recognition or reporting of
cases can not be accurately judged. However, cases are being reported from
new localities each year to a sufficient extent to justify the belief that l)oth
intensive and extensive spread is taking place. Extensive spread has certainly
occurred in eastern Montana, North Dakota, and probably South Dakota. In
Montana, until 1914, infection was definitely known in but four counties;
Missoula, Ravalli and Granite, west of the continental divide, and in Carbon
county, bordering Wyoming in the south portion of the eastern part of the
state. It has now been reported from thirty-five. The first known occurrence in
South Dakota was in 19].l; in North Dakota, 1919.

The mechanism by which spread, as indicated by the occurrence of cases
in man, is accomplished is unknown. The obvious explanation is that infection
has been established in new areas by infected ticks, either wood ticks or rabbit
ticks, carried on animals coming from old foci. Although this seems reason
able and may be the correct explanation, yet, if spread of infection is thus
easily accomplished, it is difficult to understand why it has not long ago

STATE BOARD OF ENTOMOLOGY

45

N HiH^^^^^ROCKY MOUNTAIN SPOTTED FEVER

'^»>JJ*J>~^'^"?>>i^^ DISTRIBUTION ev COUNTItS

crossed from the west to the east side of the Bitter Root Valley, or why within
two years' time it suddenly appeared over an area of approximately 30,000
square miles in eastern Montana. In the former instance, host -borne infected
ticks have unquestionably been carried from the west to the east side of the
valley for many years ; yet, if we accept the occurrence of human eases as an
index, infection has never become established, although ticks are numerous.
In the latter instance, opportunity for the introduction of infected ticks from
either of several old Carbon County foci or from Wyoming has existed for
many years. If spread from either of these established areas of infection had
been responsible it is difficult to understand why infection should have ap-
peared at many points over so vast an area in so short a time, and particularly
at points so far removed from both.

46 SEVENTH BIEXNIAL REPORT

In the above discussion, the word "spread" has been used on the sup-
position that occurrence of human cases in a new area is the result of more
or less recent introduction of the virus. But does this necessarily follow?
Is it not possible that spotted fever virus in an a virulent non-symptom producing
phase'4) has been more generally distributed throughout the Eocky Mountain
fever region than human occurrence would lead us to suppose, and that ap-
parent new foci, as indicated by first case occurrence, may in reality be sec-
tions in which changing environmental conditions have changed an avirulent
type of virus to one infectious for man? In this connection the persistent
•occurrence in the Bitter Root Valley of a mild type of the virus in the rabbit
tick, in spite of a contemporaneous highly virulent type in the wood tick,
has suggested to us tliat in non-wood tick sections a mild or even non-symptom
producing type of virus nuiy be maintained by the rabbit tick, and that, fol-
lowing wood tick introduction or increase, as has apparently occurred in nuuiy
sections of eastern Montana, passage of the virus through a greater variety
of species of host animals (rabbit ticks only passing the virus through rab-
bits) may result in an increase of infectiousness to a point at which the virus
is capable of infecting man. If this hypothesis be true it implies virus main-
tenance by the rabljit tick independently of the wood tick, and as noted else-
where, is presumably susceptible to proof by the testing of raiiliit ticks from
points far beyond the Rocky Mountain endemic region.

The idea of the existence in nature of a non-symptom producing type
of spotted fever virus is not entirely new, and was first suggested by Ricketts
in a somewhat different connection. As a matter of fact, we have frequently
encountered such a type of spotted fever virus in experimentally infected
wood ticks. Moreover, the known regional variation in virulence from the
highly fatal western Montana type to the mild southern Idaho type, suggests
that the idea of still further differentiation to an even milder form is not
unreasonable.

This discussion of spread would not be complete without further refer-
ence to the idea, so long held, that infection is absent on the east side of the
Bitter Root Valley. While it is true that no cases have originated there,
nevertheless the virus is present in nature. As thus far observed, however,
it occurs only in a non-symptom producing phase such as has been referred
to above. This has been shown with unfed adult wood ticks collected on the
east side in 1922, 1923, and 1928. When tested for the presence of spotted
fever virus by the feeding and inoculation method, *5* none have caused frank
si^otted fever, but for certain localities an immunizing phase of the virus has
been demonstrated in fully as high a percentage of the ticks as is usually
found carrying virulent infection on the west side.

The question at once suggests itself: Whether infection in this form
has long been resident on the east side, or is it the result of the more recent

(4) By "non-symptom producing phase" is meant one in whicli the specific
agent invades the tissues of the host witliout tlie causation of clinical evi-
dence of infection.

(5) By this method ticks to be tested are first fed on a guinea pig- for three days,

then removed, and if no fever develops within ten days, the same ticks are
eviscerated in salt solution and injected intraperitoneally into the same
ynimal. If fever does not deveiop in another ten days, an immunity test of
blood virus is given. If the virus is pi-esent in the ticks it will be shown:
(1) by fever following feeding, or (2) by fever following tick-viscera injec-
tion, or (3) if the ticks have immunized instead of causing frank infection,
by absence of fever foLowing each of three operations.

STATE BOARD OF ENTOMOLOGY 47

iutroductioii of highly virulent west side strains which have abruptly lost
their virulence under the changed ecological conditions? Present evidence on
this point is inconclusive. Suffice it to point out, therefore, that the problem
of spread from the west to the east side is not one of gradual encroachment
into contiguous favorable areas, but involves the bridging of a strip of un-
favorable tick country which in some parts of the valley is several miles in
width. This means that although many thousands of tick-bearing animals
must have left infected west side sections during the several decades that
west side infection has definitely been known, yet it would only be the adult
ticks carried by large animals (not immature ticks borne by rodents) that
would be likely to reach favorable east side sections. While a considerable
number of infected adult ticks must thus have been carried across the barrier
zone, the number during any one season is necessarily small. Furthermore,
of this small numl>er, only the females, from some of which the virus is
transmitted hereditarily, are dangerous as possible virus establishing agents.
For reasons too detailed to discuss in this paper, the mathematical chance
of thus establishing infection seems to be very small.

Incidence.

Annual incidence in any locality, area or region of infection, is directly
dependent on the abundance of infective ticks and those meteorological con-
ditions that determine the duration and degree of their ' activity. Indirectly
it is affected by all the factors noted above as concerned in virus mainte-
nance in nature. This results in a more or less definite though irregular
cycle of case abundance. This cycle occurs both in local foci and endemic
areas but the peaks of occurience in the separate foci within a given area
are not necessarily chronologically coincident.

The effect of meteorological conditions is most apparent in areas of con-
siderable case incidence like the Snake River valley of southern Idaho, where
a marked decline of cases occurs during periods of prolonged dry weather,
incidence again increasing following precipitation.

Agricultural development may be mentioned fts another factor affecting
annual incidence. Cases often begin to appear soon after settlement in locali-
ties not before known infected. This results from more favorable tick con-
ditions due to resultant increase in rodents and the bringing in of domestic
animals. The course of subsequent incidence depends largely on the type of
agricultural development, whether extensive or intensive, or a combination
of the two. If intensive, a point of development is finally reached beyond
which conditions become increasingly unfavorable to virus maintenance. E.x-
tensive farming, however, or a combination of extensive and intensive opera-
tions, favor continued prevalence.

Seasonal incidence is delimited by the period of adult tick activity. Most
cases occur from March to June and are usually most numerous in April and
May. They have, however, been reported during all the months in the year.
Winter cases, except under unusual conditions, come from mountainous areas.

Occupationally, the greatest incidence is among those engaged in agri-
cultural pursuits. In some areas farmers are most affected ; in others, men
engaged in the sheep industry, and in still others persons handling cattle, as
determined by the local type of agriculture. Cases also occur among pros-

48 SEVENTH BIEXNIAL REPORT

pectors, niinei'S, hunters, trnppers, railroad section hands, forest service em-
ployees, oil field workers, fishermen, picknickers, tourists and others whose
pleasure or business pursuits take them iuto infected districts. A surprising
number of cases occur among townspeople who are often in infected areas
for onlv a few hoars.

Difference in occupational exposure results in many more cases among
men than women. A ('onsideral)le proportion of cases among the latter are
•due to ticks l>rouglit home by the husband or other male mend)ers of the
liousehold.

Age incidence is also largely the result of occupational exposure, at least
as between children and adults. Incidence among children is much higher
where they actually live in infected districts (e. g.. Bitter Root Valley), than
in sectioJis where danger is mainly beyond the limits of cultivable land (e. g.,
in parts of the Snake River valley in southern Idaho).

Taljle I shows the known case prevalence in infected states by years from
1909 to 1926. The Montana record is the only one at all accurate. Some
records, for example those for recent years in Idaho, have been omitted be-
cause the data is so incomplete as to give an entirely false impression. In
fact, except for Montana the tabulation is so incomplete that it gives but a
poor idea of the incidence or of the relative prevalence in the different states.
Two good illustrations of this have recently come to our attention. One is
a letter received from a physician in northeastern California, advising that
he has treated al)out a dozen cases each year during his several years of resi-
dence ; that is, he alone has treated as many cases each year as have been
officially reported in any one season from the entire affected area within
the state. The second is a letter from a physician in Wayne County, Utah,
a supposed uninfected area, advising of the common occurrence of Rocky
Mountain spotted fever and of seventeen cases that he has treated in 1928.

Virulence.

Rocky Mountain spotted fever, so far as we are aware, is unique in the
fact that virulence, in any local endemic focus, as represented by death rate,
is reasonably constant year after year.

The Bitter Root Valley in western Montana has long been known as the
focus of greatest virulence. Accurate records for the ten-year period, 1917
to 1926, show that the mortality rate approximates seventy-five per cent.
It is about ninety per cent in adults, and fifty per cent in children. There
are, however, other sections in the northwest where the death rate is equally
or nearly as high, but less is known of them because of lesser economic im-
portance. One is a small area on Rock Creek, twenty-five miles east of the
Bitter Root Valley. There are two iu Wyoming, one on Kirby Creek near
Thermopolis, the other iu the Wind River Mountains. In southern Idaho,
near Soda Springs, an area of one hundred per cent mortality was formerly
known, but no cases have been reported since 1903.

The mildest type of the disease prevails in the Snake River valley in
Southern Idaho, where mortality seldom exceeds five per cent. Ambulatory
cases are not infrequent according to local physicians. Within this large
area, however, there are small local portions in which cases are of greater
than the average severity, though by no means approaching the extreme viru-

STATE BOARD OF ENTOMOLOGY

49

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50 SEVENTH BIENNIAL REPORT

leuce of the Bitter Eoot Valley type. In other sections of tlie northwest
the mortality ranges between ten and twenty-three per cent, being highest
in Wyoming. In some states, however, the death rate is undoubtedly less than
that shown on Table I, since records of morbidity in most affected states
are far less complete than those of mortality.

With respect to this question of virulence an interesting condition exists
in three infected canyons near Mountain Home, Idaho. The cases from each
canyon exhibit a different and quite constant degree of virulence, those from
one being quite severe, those from the next of intermediate severity, while
those from the third are mild. This condition has been noted by all the
doctors who have practiced in Mountain Home over a considerable period of
years, and apparently offers an exceptional opportunity for the study of
factors affecting virulence.

Periodic variations in virulence are believed to occur by some physicians
who have attended cases from the same focus or locality over a considerable
number of years. This is quite possible, but thus far the evidence is incon-
clusive, since it is impossible to eliminate the personal complexes of patients
and also because of the likelihood that difference in age incidence in different
years (the mortality rate increases with age), in some instances at least, offers
an explanation of varying death rate.

The cause of local or regional difference in virulence as manifested in
human cases, is obscure. Wolbach has stated that "rapidly repeated passages
of the virus during a long period in a single species of animal, peculiar to or
particularly abundant in a given locality, would conceivably modify the viru-
lence in man. ' ' This seems to be a reasonable possibility and is perhaps
not an unlikely explanation of the low virulence which prevails in areas such
as the sagelirush desert country of southern Idaho, in which susceptible host
species are few and rabbits are the dominant hosts of early stage ticks. We
have given some thought to this phase of the disease complex, but have ar-
rived at no definite conclusion. The prolonged life cycle of the tick (seldom
completed under two years) and the fact that in nature the successive stages
feed at intervals approximating a year, and the numerous possible factors
involved, have thus far stood in the way of laboratory experiments along this
line. Of the possible explanations which have occurred to us, we have felt
that the most reasonable one and the one which best fits the known epidemi-
ological data is, tliat virulence varies with the number of susceptible species
of small mammals through which infection is being passed in any given
endemic focus. This checks well with the present knowledge of animal life
in various foci, but for conditions outside Montana, this is admittedly scanty.
The idea is purely hypothetical. It is possible that there are localities in
which, due to local ecology, the mild type of infection borne by the rabljit
tick affects the virulence of the virus as carried to man by the wood tick,
l)ut no such relationship exists in the Bitter Root Valley where both species
are abundant.

Etiology.

The virus of Eocky Mountain spotted fever belongs to the rickcttsiae
which Wolbach (1925) is certain represents a new group of micro-organisms.
The spotted fever rickettsia was first observed by Ricketts in blood smears
but it was through Wolbach 's carefully controlled experiments (1916-1919)
checked by human autopsy findings that it was definitely established as the

STATE BOARD OP ENTOMOLOGY SI

casual agent of the disease. For it he proposed the name, I)ermacentroxenus
ricl-ett.Hi. His results have since been confirmed by Nicholson, Cowdry, No-
giichi and ourselves.

We can find no coiiniion meeting ground with Woodcock, who believes
that rii'kettsiao are not micro-oiganisms, but products of celluhir digestion.

Observations on the Virus.

Although the virus of Rocky Mountain spotted fever has been studied
by several investigators, their results, for the most jtart are not essential
to the purpose of this paper, and it is only intended to discuss the more
significant findings of Sui'geon R. R. Spencer and the writer.

Of greatest significance, because it in part led to the later production
of a vaccine, Avas the observation that there are definite differences between
the virus as it occurs in the cold blooded intermediate host, i. e., tick virus,
and in the blood of man and lal)oratory animals, i. e., blood virus. The more
important of these are:

1. In our experience and that of other investigators the properties of
blood-virus remain essentially constant throughout an indefinite number of
animal passages. It is always an infectious and never an immunizing virus.
In ticks, on the other hand, it alternates between a non-symptom and im-
munity producing phase that is present in aestivating and hibernating ticks
and an extremely virulent, infectious phase, which, in each successive stage
of the tick, follows the ingestion of fresh blood. This transition we have
termed "reactivation" but what happens in the tick to Ijring it about fol-
lowing the ingestion of blood we do not know. It can scarcely be a simple
multiplication of rickettsia since they are often present in abundance before
blood is ingested.

2. Tick-virus is much more concentrated than blood-virus. An average
c.c. of the latter contains 500 M. I. D. for a guinea pig. One c.c. of reac-
tivated tick-virus, on the other hand, which is equivalent to the pooled viscera
of one hundred adult ticks that have fed three days, may contain from 100,000
to 1,500,000 M. I. D. That is, volume for volume, tick-virus is two hundred
to three thousand times more concentrated. Single ticks usually contain
from 1,000 to 15,000 M. I. D.

3. The third difference is that whereas blood-virus Avill not infect
tluough the unabraded skin, tick-virus will do so readily. For lack of an
exact term — since we do not know the controlling factor — we have called this
quality of tick-virus "aggressiveness."

4. Blood-virus alone, whether killed or attenuated by heat or chemicals,
does not immunize. Tick-virus when killed by either phenol, formalin, chloro-
form or alcohol, has high protective value.

Other observations made on the virus in recently infected adult ticks have
thrown some light on what happens in previously non-infected ticks following
the ingestion of blood-virus. There first appears to be a transition period
during which the virus loses its blood-virus characteristics and takes on those
of tick-virus. This is followed by a period of invasion during which the para-
site becomes generally distributed throughout the tick tissues. During this
time, which may be a matter of days or weeks, the tick is unable to transmit
infection by feeding. This is in spite of the fact as noted below that the
vii'us content of individual ticks during the period of invasion may be as
high as 15,000 M. I. D. per tick, and is evidently because the virus has not

52 SEVENTH BIENNIAL REPORT

yet reached the salivary glands. This explains the difficulty that has been
experienced by some investigators in transmitting infection with recently in-
fected adult ticks, and which has not necessarily been due, as some have sup-
posed, to failure of the tick to acquire infection. Since ticks cannot infect
by feeding during these two periods their occurrence has been demonstrated
by the daily inoculation into guinea pigs of the viscera of the recently in-
fected adults. The same phenomena of transition and invasion must also
occur if the infective blood meal is ingested by the larva or nymph, but in the
early stage ticks they are not so easily demonstrated because of the difficulty
in getting immature ticks to feed a second time. In them, however, invasion
is probably more rapid, because the tissue changes accompanying transfor-
mation undoubtedly facilitate and speed up the generalized distribution of
the parasite.

Thus far no one has succeeded in showing any morphological cycle of the
virus, although it seems quite possible that one occurs. Wolbach has de-
sciibed three morphological forms and the sequence in which they appear
in nymphal ticks. While we are confident that these and other types which
have been described are all manifestations of the disease agent, we feel that
our own studies show that the virus is also frequently present in a form that
is either ultra-microscopic or is non-demonstrable by methods that have been
used. Our experimental evidence to this effect consists first of results of
the testing of individual ticks of numerous laboratory reared lots, each lot
consisting of ticks from the same parent female, infected as larvae on the
same host, and of subsequent identical history until tested as adults. Each
tick was tested by the examination of smears of six tissues for the presence
of rickettsia and the inoculation of the remaining viscera into a guinea pig
to test infectiousness of the virus content. Of each lot thus tested, the larger
j)ortion of the ticks showed correlation between abundance of rickettsia and
infectiousness, but there were always two smaller groups in one of which the
ticks were non-infectious although rickettsia were present and often numerous,
while in the other the ticks were infectious but rickettsia could not be dem-
onstrated. The second line of evidence is from ticks infected as adults. In
these it frequently happens that titration will show a virus content of 10,000
to 15,000 M. I. D. for a guinea pig per tick before any rickettsia invasion
of the tick tissues can be shown. The same lot of ticks tested later, however,
will show rickettsia in the greatest abundance, even though the virus content
in M. I. D., as sometimes happens, may have become considerably reduced.
We also consider the well-known scarcity of rickettsia in blood-virus as further
evidence in support of our contention.

Other results of our virus studies have either been detailed in earlier
papers or will be discussed in others which will appear in the near future.

Kuczynski and Brandt claim to have cultivated the rickettsia of Eocky
Mountain spotted fever and believe it to be a variant of Protexbs X-19. On this
relationship we have no opinion to express. Their culture work has not been
verified and until this is done it must be accepted that Wolbach and Schlesin-
ger are the only ones who have approached successful cultivation of the virus.
Their results, however, were secured by a tedious process of tissue culture,
which is not practicable for routine work.

Studies of the virus of Rocky Mountain spotted fever are potentially
of more than specific importance. Of the several recognized rickettsia dis-

STATE BOARD OF ENTOMOLOGY 53

eases, it is the only one that is satisfactorily reproduced in laboratory animals
(human infection is almost perfectly reproduced) and the only one in which
the use of the intermediate host for experimental purposes is not markedly
restricted. In spotted fever studies, therefore, a much wider range of experi-
mentation is possible and it offers consequently the best avenue for the study
of the characteristics of tliis group of micro-organisms.

Mechanism of Human Infection.

Eicketls stated that human infection "would seem to consist of the
injection of salivary secretion, laden with virus, into the cutis of the host."
Certainly we must agree with this view in the majority of cases.

Most persons becoming infected with spotted fever give definite history of
tick bite from two to ten or twelve days before onset. A minority, however,
]»erhaps five per cent, deny the possibility of having been infected in this
way. While in most instances it is safe to assume that they have been mis-
taken, yet the fact that tick bite has almost certainly not occurred in four
of nine cases originating in our own laboratory has caused us to give credence
to some of those negative reports. Heretofore, our tick-bite-negative labora-
tory cases were assumed, for lack of a better explanation, to have become in-
fected by contamination of an abrasion with blood-virus, a well recognized
danger. The explanation was unsatisfactory in several of these cases, how-
ever, because of the appaicnt absence of any demonstrable abrasion.

Recent experiuients are of some interest in this connection. It has long
been known that blood-virus of experimental animals would not pass the
unabraded skin, nor would it infect if ingested. The possibility that tick-
virus would act differently was not considered imtil a short time ago. In an
exceptionally clear-cut series of tests it was shown that tick-virus (which our
previous experiments have shown volume for volume to contain many times more
infectious doses than blood- virus) would infect if merely dropped among the
hairs on to the unabraded skin of guinea pigs ; also if dropped into the eye.
In another series of tests it has been demonstrated, contrary to previously
accepted ideas, that tick excrement is frequently infectious, but tests to de-
termine Avhether it will cause infection by contamination of the unabraded
skin have not jet been made.

These findings, we believe, furnish an explanation of our hitherto not
satisfactorily explained laboratory cases, all but two of which have occurred
in laboratory attendants who were engaged in rearing infected ticks for mak-
ing vaccine. They also suggest that spotted fever may occasionally at least
be acquired in nature without tick bite. Opportunity for this is afforded by
the custom of hand-picking ticks from domestic animals. In so doing, ticks —
engorged or partly engorged females especially — are not infrequently rup-
tured by pressure of the fingers, or the fingers may come in contact with the
tissues of ticks ruptured while on the host. The fingers thus contaminated
may conceivably transfer highly infectious tick-virus to some easily pene-
trated portion of the skin or to the conjunctivae, as is known to happen fre-
quently in tularaemia.

Prevention.

There are two avenues along which the problem of prevention has been
approached; (1) wood ti,ck control with the object of keeping the agent of
human infection at a point of uiinimum abundance, and (2) personal prophy-
laxis.

54 SEVENTH BIENNIAL REPORT

Wood Tick Control. In most sections of the northwest spotted fever
has been prevalent in more or less sparsely settled sagebrush areas of low
value, largely used for range purposes, and territorially infection has been
dilute. Although the disease has been greatly dreaded, economic pressure
in most sections has not been acute. The Bitter Root region of infection,
however, is a fertile mountain section of high priced agricultural laud and
denser population. From this valley came an incessant demand for investi-
gation and control, wliich finally resulted in the beginning of research work
in 1902, and in 1911, of tick control operations which have been continued
to the present time. From a small beginning, they have gradually extended
until control work, as now carried on by the Montana State Board of Ento-
mology, covers a strip of land approximating seventy miles long and from
three to fifteen miles in width along the west side of the valley. The meas-
ures used have been dipping, hand-picking and grazing control of domestic
stock, and the destruction of rodents, the first three methods being directed
against female ticks to prevent egg deposition, the last against the immature
stages to prevent them from becoming adults. After eighteen years of work
it must candidly be admitted that the results have been far from satisfactory.
This has been due in part to inadequate operating funds, in part to lack of
permanency of results, and in part to the fact that procedure has been based
on a too superficial knowledge of the relative importance of the separate
factors of the local complex that controls maintenance. The last deficiency
has in considerable measure been removed by the recent ecological studies of
the Public Health Service. These have indicated that the most fundamental
factors of maintenance that affect the prevalence of infection in the valley
have their seat in the mountains that border it on the west. From these
infection overflows each year to pour down into the valley. The first aim
of control, then, should be shutting off the flow of infection, and in the light
of this knowledge the efficiency of present control methods, which only apply
to valley conditions, may be compared to that of one who attempts to ex-
tinguish a forest fire from the windward side, or to relieve the flooded valley
of the Mississippi through operations at New Orleans.

To this end our studies have further indicated that the elimination of
the Rocky Mountain goat is the most important single step to be taken. The
ranges of this animal, because of its habits and its efficiency as an adult tick
host, are areas of heavy wood tick concentration and are veritable reservoirs
of the virus. For the present, however, no changes in control methods are
contemplated by the Montana State Board of Entomology pending determi-
nation of the value for control purposes of the tick parasite, Ixodiyliag-us
caucurtei Du Buysson. Work with this parasite which was brought into the
state in 1926 through the courtesy of Drs. Wolbach and Larousse is being
carried on by Professor 11. A. Cooley, Secretary of the above Board.

No attempt to control Rocky Mountain spotted fever in any other section
of the Rocky Mountain region has yet been made. This has been due to the
great expanse of country involved, to the absence in other sections of so acute
an economic condition as that in the Bitter Root Valley, and to inability to
recommend practical methods of attack. Unfortunately, the siutation is
further complicated because the factors of maintenance differ so widely in
different localities that on the basis of present knowledge no one control pro-
gram could generally )je .'ipplied. Indeed, in many localities, specific research

STATE BOARD OP ENTOMOLOGY 55

problenis would be involved. Still another complication is introduced by the
lack of evaluation of the exact part played by the rabbit tick in maintaining
infection. If this tick is capable of maintaining infection independently
of the wood tick, it is a point of considerable importance, especially in re-
spect to the degree of pernmnency of control results.

Personal Prophylaxis. Attention has just been directed to the fact
that in the present status of our knowledge the initiation of wood tick control
measures has not been feasible outside the limits of the Bitter Eoot Valley
and that even there the results have been unsatisfactory. Personal prophy-
laxis must therefore be relied upon for protection against infection. The
most effective measure is the avoidance of known tick infested or infected
areas. Next best is the examination of the clothing and body for ticks. Field
workers on control and investigation work do this at frequent intervals, but
for the person exposed to average danger, twice a day would be usually suffi-
cient. This results from two fortunate facts, (1) that ticks usually crawl
about the body or clothing for some time before attaching and (2) that ticks
are seldom able to infect until some hours after feeding has begun, the virus
as we have shown, not being infective until reactivation has taken place.
The shortest known interval was recorded by Rieketts, one hour and forty-
five minutes, onh once. Probably ten hours or longer is more frequent and
we have often known of ticks, later proven infective that fed on guinea pigs
for three days with negative results.

Except for the wearing of some type of apparel that prevents ticks from
crawling up inside the trousers legs, the idea of wearing tick proof clothing
is not approved.

These measures of prevention, however, are far from one hundred per
cent effective. In spite of careful examination of clothing, ticks may hide in
seams or folds of the cloth and later become a source of danger to the person
himself, his family or others. Cases originating in this manner are not
uncommon. An extreme illustration is the case of a woman who, at time of
infection had been confined to bed for over a month. There are numerous
records of double infection by the same tick in persons occupying the same
bed, and the writer knows of one instance of three persons, who were infected
at points fifteen and twenty miles apart by the same tick. Unsuspecting
persons have also been infected by ticks from stock shipped from infected
districts.

Because of the impossibility of one hundred per cent protection against
tick bites, vaccination is now being recommended. An effective vaccine has
long been sought. The first experimental vaccine was prepared by Rieketts.
This was a live virus-immune serum mixture, ))ut because of its live virus
content, it could not wisely lie used for human prevention. In 1923, Noguehi
announced the production of another sero-vaccine in which the virus content
had been killed by heat. While this successfully protected guinea pigs, it was
later proven valueless in monkeys and man. The vaccine which is now being
used is one prepared by the Public Health Service, and which during the past
four years has been sufficiently tested to justify the statement that it is of
definite value.

In a preceding section it has been noted that spotted fever virus in ticks
passes through an immunity-producing stage. Although immunity production
by the injection of tick tissues or eggs had previously been observed (Rieketts,

56 SEVENTH BIENNIAL REPORT

Davis, Fricks, Parker) no one had happened to encounter it on a sufficient
scale to fully realize the potentialities. This realization came to us as the
result of mass work. In the spring of 1922 thousands of unfed adult ticks
were collected from nature and injected intraperitoneally into guinea pigs to
test for the presence of spotted fever virus. If infected they consistently im-
munized and never caused clinical spotted fever. This was followed by the
observation that otlier thousands of fed ticks, collected from animals and
similarly tested, invariably produced typical infection. The deduction of the
phenomenon of reactivation naturally followed. Next came the demonstration
of the high concentration of the reactivated tick-virus and the discovery that
chemically killed tick-virus, in contradistinction to similarly killed blood-virus,
stimulated the formation of protective bodies in guinea pigs. Subsequent tests
showed that it would also protect rabbits, monkeys, and finally man.

The method of vaccine production is unique. At present it is prepared
as follows : Larval ticks are engorged on infected rabbits and reared to the
adult stage. As adults they are fed several days on guinea pigs to reactivate
the virus, are then ground and thoroughly comminuted with sterile sand, and
suspended in salt solution which contains four ticks per c.c. and two per cent
of a virus killing agent and preservative that consists of four parts phenol and
one part formalin. Subsequently two dilutions are made. After seven days
the ticK tissue and sand are thrown down by centrifugation. The supernatent
salt solution containing the killed virus constitutes the vaccine, one c.c. of
which contains the killed virus content of one tick and five tenths of one per
cent of the preservative. The better portion of a year is required for
preparation.

However, tests nmde within the last year suggest that the tedious and
dangerous process of rearing hundreds of thousands of infected ticks from
larva to adult, which has been responsible for most of our cases of laboratory
infection, can be abandoned and the vaccine prepared from ticks infected as
adults. For this method unfed adults will be collected from nature in the
spring (previous infection does not matter), fed two days on infected guinea
pigs, left for two weeks at room temperature to insure generalized invasion of
the tick by the virus, and then placed in refrigeration. In the fall they will
again be placed at room temperature and shortly given a second, or virus-
reactivating blood meal, then made into vaccine. If this method proves as
successful as now indicated, both time and expense will be saved and the
danger to our laboratory workers materiallj^ lessened.

The value of this vaccine for human prophylaxis has been under test for
tlie past four years. One test was made in the Snake Eiver valley in Southern
Idaho, against the mildest known type of infection. The area selected was
one of relatively high case incidence in which a large proportion of the cases
occurred in men handling sheep on the range. This made it possible to restrict
the test to this one industry. During 1926 and 1927, 193 sheepherders were
vaccinated, 364 nonimmunes serving as controls. A single case occurred
among the vaccinated men, one in 193. This was a man who took but one
injection of vaccine. Among the 364 controls there were 22 cases, 1 in every
16.55 men.

For the past four years a second and contrasting test has been under way
in the Bitter Eoot Valley against the most virulent known type of infection.
Here a total of 2,049 persons have been vaccinated, some one, some two, some

STATE BOARD OF ENTOMOLOGY 'oi

tliiee and some foui- years. This group of vaccinated j^ersons is divisiljle into
two subgroups ; one consisting of 59 highly exposed laboratory and control
workers, the other of residents exposed only to ordinary danger. In the
former highly exposed group eight cases of infection have occurred with seven
recoveries and one death. This is in marked contrast to the fact that before
the vaccine was in use, five cases and five deaths — 100 per cent mortality —
had occurred in laboratory workers, all of whom were working with Bitter
Eoot valley strains. Among the larger group of 1,990 persons exposed to
ordinary danger four eases have occurred, all of which have recovered. This
is again in marked contrast to the occurrence of 18 cases and 15 deaths among
non-vaccinated persons of equal exposure in the same area.

During 1927 and 1928 the vaccine has been quite widely used outside the
test areas especially in Montana and Wyoming. Of 2,104 persons so vaccin-
ated only two have become infected. These were both from the highly virulent
Kirby Creek focus in Wyoming and have been the only recoveries of seven
cases originating there in the past three years.

These results suggest that the vaccine commonly confers full protection
against the milder types of spotted fever and ordinarily affords a sufficient
degree of protection against the virulent types to ensure recovery. The Bitter
Root results further suggest that a better degree of protection is given against
strains from nature than against laboratory strains.

The duration of any considerable degree of protection rarely exceeds one
year, but accumulating evidence suggests there is an accelerated immunity in
persons vaccinated in successive seasons, such as often results from repeated
use of smallpox vaccine. Reactions froiii vaccination, for the most part, are
quite mild'.

Thus far, the demand for the vaccine has exceeded the supply. While it
evidently has a definite field of usefulness, because of high cost and the
need of yearly vaccination we do not consider it as an ultimate major factor
in the solution of the spotted fever proldem.

Conclusion.

In the preceding pages an attempt has been made to convey a compre-
hensive conception of the progress that has been made toward the solution
of the Rocky Mountain spotted fever problem. Direct discussion of the eco-
nomic importance of this disease has thus far been omitted, in part because
this has to some extent been indicated in the context under the various
headings, but chiefly that it might be pointed out in concluding that Rocky
Mountain spotted fever in reality, is but one phase of a still larger problem
that confronts the affected states, namely, what, for lack of a better designa-
tiou may be called the "wood tick problem."

Spotted fever, though the most important, is but one of several ills that
Jjcrmacentor andersoni inflicts upon the Rocky Mountain region. In man
it also causes tick paralysis, is responsible for numerous cases of tularaemia,
and in some parts of Wyoming and Colorado, at least, transmits apparently
a still different infection, an intermittent type of fever, of unknown etiology.
There are also on record numerous cases of septic infection and other patho-
logical conditions which are credited to secondary infection at the site of tick
bite. Losses among domestic animals are far from a small item. Sheep and
cattle are most commonly affected, especially the former. Tick paralysis in

58 SEVENTH BIENNIAL REPORT

sheep has been known since 1914 when first described by Hadwen. Eecently
the writer with the co-operation of Dr. James Dade, chief sheep inspector of
the Idaho State .Sheep Commission, and Dr. W. J. Butler, State Veterinary
Surgeon of Montana, was able to prove wood tick transmission of tularaemia
to sheep. The losses from this cause are considerable, and are doubtless
occurring over a far wider area than we have knowledge of at the present
time. In some sections cattle are commonly affected by a condition similar
to tick paralysis as recognized in sheep. And last, but by no means least, is
the mental worry to which tens of thousands of families in the affected region
are subjected each year during the tick season, and to a greater and greater
extent each year the dread of tick borne infection is preventing the enjoyment
of the opportunities for outdoor life which constitute one of the greatest
natural assets of the Eocky Mountaiii region.

Montana has been forced to an active recognition of this tick problem not
only by the acute situation in the Bitter Eoot Valley, but also by the recent
rapid spread of spotted fe\er over a large part of the state. As a result this
state has but just completed at Hamilton, in the Bitter Eoot Valley, a $60,000
laboratory erected for the sole purpose of accommodating the state and
federal agencies that are working on wood tick-l)orne and wood tick-caused
pathological conditions of man and domestic animals. Although the wood tick
problem has been less acute in other affected states, it has nevertheless been
serious, and is becoming increasingly so as agriculture continues to push out
and develop new sections continually creating more favorable tick conditions
and new areas of infection.

As viewed from the standpoint of our present knowledge the only satis-
factory solution of this larger tick problem is a practical means by which ticks
can be kept at a point of minimum abundance. Considering the unsatisfactory
status of tick control procedure and the vast areas of tick infested moun-
tainous or otherwise noncultivable land that are involved it is to be earnestly
hoped that the tick parasite work now being conducted by the Montana State
Board of Entomology will, in some measure at least, aid in the solution of
the problem.

REFERENCES.

Anderson, J. F. Spotted Fever (Tick Tevcr) of the Eocky Mountains; a New

Disease. U. S. Pub. Health and Marine Hosp. Service, Hyg. Lab. Bull.,

No. 14, pp. 1-50, 190.3.
Becker, F. E. Investigations on Eocky Mountain Spotted Fever in Colorado.

Jour. Inf. Dis., Vol. 39, No. 1, pp. 81-88, July, 1926.
BiSHOPP, F. C. The Distribution of the Eocky Mountain Spotted Fever Tick.

Bur. of Ent., U. S. Dept. Agri., Cir. No. 136, pp. 1-4, Mar. 31, 1911.
BiSHOPP, F. C, and King, W. V. Additional Notes on The Biology of the

Eocky Mountain Spotted Fever Tick. Jour. Econ. Ent., Vol. 6, No. 2,

pp. 200-211, April, 1913.
COOLEY, E. A. Tick Control in Eelation to Eocky Mountain Spotted Fever.

Mont. Agri. Exp. Sta., Bull. No. 85, pp. 1-29, May, 1911.
The Spotted Fever Tick (Dermacentor venusius Banks)

and Its Control in the Bitter Eoot Valley, Montana — a Eeview. Jour.

Econ. Ent., Vol. 8, No. 1, pp. 47-53, Feb. 15, 1915.

STATE BOARD OF ENTOMOLOGY 59

The Spotted Fever Tick. Special Bull. No. 26, Mont.

State Bd. of Health, pp. O-l.'i, June, 1923.
Eeports as Secretary of the Montana State Board of

Entomolog}', Biennial Reports of, 1 to 6, 1915-1927.
CowDRY, E. V. The Distribution of Rickettsia in the Tissues of Insects and

Arachnids. Jour. Exp. Med., Vol. 37, No. 4, pp. 431-4.56, April 1, 1923.
Rickettsiae and Disease. Arch, of Path, and Lab. Med.,

Vol. 2, pp. 59-90, July, 1926.
Davis, B. F. Unfinished Experiments of Dr. Howard T. Ricketts on Rocky

Mountain Spotted Fever. Ann. de I'Inst. Pasteur, Vol. 22, p. 541, 1908.
FooTE, N. C. Rocky Mountain Spotted Fever in the Domestic Rabbit. Jour.

Med. Res., Vol. 34, No. 4, pp. 495-507, March, 1919.
Fricks, L. D. Rocky Mountain Spotted Fever. A Report of its Investigation

and of Work in Tick Eradication for its Control in 1913. Pub. Health

Rpts., Vol. 29, No. 8, pp. 449-461, Feb. 20, 1914. Reprint 169.
Rocky Mountain Spotted (or Tick) Fever, Sheep Grazing

as a Possible Means of Controlling the Wood Tick {Bermacentor ander-

soni) iu the Bitter Root Valley. Pub. Health Rpts., A^ol. 28, No. 32,

pp. 1,647-1,653, Aug. 8, 1913. Reprint 139.
Rocky Mountain Spotted Fever. Some Investigations made

during 1912 by Passed Assistant Surgeon T. B. MeClintic. Pub. Health

Rpts., Vol. 29, No. 17, 15 pp., Apr. 24, 1914. Reprint 188.
Rocky Mountain Spotted Fever. A report of its Investi-
gation and of Measures Undertaken for its Eradication During 1914.

Pub. Health Rpts., Vol. 30, No. 3, 19 pp., Jan. 15, 1915.
Henshaw, W. H., and Birdseye, C. The Mammals of Bitter Root Valley,

Montana, in Their Relation to Spotted Fever. Bur. Biol. Surv., U. S. Dept.

Agri., Cir. No. 82, pp. 1-24, Aug. 3, 1911.
Hertig, M., and Wolbach, S. B. Studies on Rickettsia-like Micro-organisms

in Insects. Jour. Med. Res., Vol. 44, No. 3, pp. 329-374, March, 1924.
Hunter, W. D., and Bishopp, F. C. The Rocky Mountain Spotted Fever

Tick. With Special Reference to the Problem of its Control iu the Bitter

Root Valley, Montana. Bur. of Ent., U. S. Dept. Agri., Bull. No. 105,

pp. 1-47, 1911.
Kelley, F. L. Rocky Mountain Spotted Fever — Its Prevalence and Distrilni-

tion in Modoc and Lassen Counties, California. Calif. State Jour. Med.,

Vol. 14, p. 407, October, 1916.
Kuczynski, M. H., and Brandt, E. Neue atiologische und pathogenetische

Untersuchungen in der "Riekettsiengruppe. " Krankheitsforschung, Bd.

3, H. 1, pp. 26-74, 1926.
Die Erreger des Fleck- und Felsenfiebers, Biologische and

Pathogenetische Studien. Julius Springer, Berlin, pp. 1-256, 1927.
La Bier, C. R. Rocky Mountain Spotted Fever in Indiana. Jour. Ind. State Med.

Assoc, Vol. 18, pp. 418-419, Nov. 15, 1925.
Mayer, M. B. Transmission of Spotted Fever by other than Montana and

Idaho ticks. Jour. Infect. Dis., Vol. 8, p. 327, 1911.
Transmission of Spotted Fever by the Tick in Nature.

Jour. Inf. Dis., Vol. 8, p. 322, 1911.

60 SEVENTH BIENNIAL REPORT

Maxey, E. E. Eocky Mountuiii Spotted (Tick) Fever; with Special Eeference
to Casual Factors, Mortality and Geographical Distribution in Idaho.
Med. Sentinel, Vol. 16, December, 1908.

McClintic, T. B. Investigations of and Tick Eradication in Rocky Mountain
Spotted Fever. U. S. Pub. Health Epts., Vol. 27, No. 20, 31 pp., Mav
17, 1912.

Moore, J. J. Time Relationships of the Wood Tick in the Transmission of
Eocky Mountain Spotted Fever. Jour. Infect. Dis., Vol. 8, p. 339, 1911.

Nicholson, F. M. A Cytological Study of the Nature of Eickettsia in Eocky
Mountain Spotted Fever. Jour. Exp. Med., Vol. 37, No. 2, pp. 221-230,
Feb. 1, 1923.

NOGUCHI, H. A filter Passing Virus, Obtained from Dcrmacentor ander-
soni. Jour. Exp. Med., Vol. 44, No. 1, pp. 1-10, July 1, 1926.

Immunity Studies of Eocky Mountain Spotted Fever.

I. — Usefulness of Immune Serum in Suppressing an Impending Infection.
Jour. Exp. Med., Vol. 37, No. 3, pp. 383-394, March 1, 1923.
II. — Prophylactic Inoculation in Animals. Same, Vol. 38, No. 5, pp.
60O-626, Nov. 1, 1923.

Parker, E. E., and Wells, E. W. Some Facts of Importance Concerning the
Rocky Mountain Spotted Fever Tick in Eastern Montana. Mont. State
Bd. Ent., Second Bien. Ept., pp. 45-56, January, 1917.

Parker, E. E. Some Eesults of Two Years' Investigations of the Eocky
Mountain Spotted Fever Tick in Eastern Montana. Jour. Econ. Ent.,
Vol. 11, No. 2, pp. 189-194, April 18, 1918.

Report of Tick Control Operations in the Bitter Root

Valley during the Season of 1918: Reccommendations for the Further
Prosecution of the Work. Mont. State Bd. Ent., Third Bien. Ept.,
pp. 25-40, January, 1919.

Second Eeport on Investigations of the Eocky Mountain

Spotted Fever Tick in Eastern Montana. Mont. State Bd. Ent., Third
Bien. Ept., pp. 41-54, January, 1919.

The Present Status of the Control of Dermacentor

venustus Banks in the Bitter Eoot Valley, Mont., and new Data Concern-
ing the Habits of the Tick. Jour. Econ. Ent., Vol. 13, No. 1, pp. 31-37,
February, 1920.

Eeport of Tick Control Operations in the Bitter Root

Valley During the Seasons of 1919 and 1920. Mont. State Bd. Ent.,
Fourth Bien. Rpt., pp. 18-44, January, 1921.

-: Tick Control Program for 1919. Mont. State Bd. Ent.,

Clr. 1, pp. 1-23, March, 1919. Same revised, pp. 1-20, March, 1921.

Maintenance of the Virus of Rocky Mountain Spotted
Fever in Nature with Particular Eeference to Conditions in the Bitter
Eoot Valley. Special Bull. No. 26, Mont. State Bd. of Health, pp. 33-40,
June, 1923.

Transmission of Eocky Mountain Spotted Fever by the

Rabbit Tick, Haemapliy sails leporis-pahtstris Packard. Anier. Jour. Trop.
Med., Vol. 3, No. 1, pp. 39-45, January, 1923.

STATK BOARD OP ENTOMOLOGY 61

, Jiiid PoLLiNGEK, W. E. Eeport of Tick Control Operations

in the Bitter Eoot Valley During the Season of 1921-1922. Mont. State
Bd. Ent., Fifth Bien. Ept., pp. 16-29, January, 1923.

Parker, E. E., and Spencer, E. E. Eocky Mountain Spotted Fever. Eick-
ettsia-like Organisms and Infectiveness of Ticks. Pub. Health Epts., Vol.
41, No. 11, pp. 461-469, March 12, 1926.

, and Distribution and Spread of Eocky

Mountain Spotted Fever in Montana. Mont. State Bd. Ent., Sixth Bien.
Ept., pp. 19-28, January, 1927.

, and , and Francis, E. Tularaemia In-
fection in Wood Ticks of the Species Dermacentor andersoni Stiles, in the
Bitter Eoot Valley, Montana. Pub. Health Epts., Vol. 39, No. 19,
pp. 1,057-1,073, May 9, 1924.

EiCKETTS, H. T. The Transmission of Eocky Mountain Spotted Fever by the
Bite of the Wood Tick {Bermacentor occidentalis). Jour. Amer. Med.
Assn., Vol. 47, p. 358, 1906.

The Bite of the Wood Tick {Bermacentor occidentalis)

in Eocky Mountain Spotted Fever, and the Susceptibility of Local Animals
to this Disease. Jour. Anier. Med. Assn., Vol. 49, p. 24, 1907.

Further Experiments with the Wood Tick in Eelation to

Eocky Mountain Spotted Fever. Jour. Amer. Med. Assn., Vol. 49,
p. 1,278, 1907.

A Summary of Investigations of the Nature and Means

of Transmission of Eocky Mountain Spotted Fever. Trans. Chic. Path.
Soc, 1907.

A Micro-organism Which Apparently Has a Specific Ee-

lationship to Eocky Mountain Spotted Fever. Jour. Amer. Med. Assn.,
Vol. 52, p. 379, 1909.

Some Aspects of Eocky Mountain Spotted Fever as Shown

by Eecent Investigations. Medical Eecord, Vol. 76, p. 842, 1909.

, and Gomez, L. Studies on Immunity in Eocky Mountain

Spotted Fever. Jour. Inf. Dis., Vol. 5, p. 221, 1908.

Eucker, W. C. Eocky Mountain Spotted Fever. Pub. Health Epts., Vol. 27,
No. 36, p. 21, Sept. 6, 1912. Eeprint No. 96.

Spencer, E. E. A Case of Typhus like Fever following Tick Bite. Public
Health Epts., Vol. 41, No. 45, pp. 2,523-2,524, Nov. 5, 1926.

Spencer, E. E., and Parker, E. E. Eocky Mountain Spotted Fever: Infectiv-
ity of Fasting and Eecently Fed Ticks. Pub. Health Epts., Vol. 38, No. 8,
pp. 332-359, Feb. 23, 1923. Eeprint No. 817.

, and Eocky Mountain Spotted Fever:

Viability of the Virus in Animal Tissues. Pub. Health Epts., Vol. 39,
No. 2, pp. 55 to 57, Jan. 11, 1924.

--, and Eocky Mountain Spotted Fever:

Experimental Studies on Tick Virus. Pul). Health Epts., Vol. 39, No. 48,
pp. 3,027-3,040, Nov. 28, 1924. Eeprint No. 976.

62 SEVENTH BIEXXlAL REPORT

, and Rocky Mountain Spotted Fever:

Nor.-Filterability of Tick and Blood Virus. Pub. Health Rpts., Vol. 39,
No. 52, pp. 3,2nl-3,2.i5, Dec. 26, 1924. Reprint No. 982.

, and Rocky Mountain Spotted Fever:

Vaccination of Monkeys and Man. Puli. Health Rpts., Vol. 40, No. 41,
pp. 2,159-2,167, Oct. 9, 1925.

, and Rocky Mountain Spotted Fever:

Certain Characteristics of Blood Virus. Pub. Health Rpts., Vol. 41, No.
35, pp. 1,817-1,822, Aug. 27, 1926. Reprint 1,105.

Stiles, C. W. A Zoological Investigation into the Cause, Transmission and
Source of Rocky ^Mountain Spotted Fever. U. S. Pub. Health and Marine
Hosp. Service, Hyg. Lab. Bull., No. 20, pp. 1-119, 1905.

Wilson, L. B., and Crowning, W. M. Studies in Pyroplasmosis Uominis.
Jour. Infect. Dis., Vol. 1, No. 1, pp. 31-57, Jan. 2, 1904.

WoLBACH, S. B. Studies on Rocky Mountain Spotted Fever. Jour. Med. Res.,
Vol. 41, No. 1, pp. 1-197, November, 1919.

The Rickettsiae and Their Relationship to Disease. Jour.

Amer. Med. Assoc, Vol. 84, pp. 723-728, March 7, 1925.

, and ScHLESiNGER, M. J. The Cultivation of the Micro-
organisms of Rocky Mountain Spotted Fever. (Da-maeentroxenus rich-
ettsi) and of Typhus (Rickettsia protvaseki) in Tissue Plasma Cultures.
Jour. Med. Res., Vol. 44, No. 2, December, 1923.

STATE BOARD OP ENTOMOLOGY 63

ROCKY MOUNTAIN SPOTTED FEVER IN MONTANA, i' 1927-1928.

By

E. R. Parker,

Special Expert, U. S. Public Health Service

During the biennium since tlie publication of the Sixth Biennial Report
of the State Board of Entomology, 64 cases of Rocky Mountain Spotted Fever
have occurred in Montana, 3.1 during the season of 1927 and 29 during that
of 1928.

In the old western Montana area of virulent infection which includes
most of the west side of the Bitter Root Valley and the major portion of the
Bitter Root Mountains, there have been 10 cases, 2 less than during the pre-
ceding l^iennium.

Of the four persons that were infected in 1927, three in Ravalli and one
in Missoula County, only one died, a boy of 12 years of age, whose family
had but recently moved into the infected district. He had not been vaccinated.
Of the three recovered cases, two had received the Pul>lic Health Service vac-
cine and had relatively mild courses of infection. The third was a l)oy living
on the east side of the valley, near Missoula. He was presumably infected by
a tick brought from west of the river hy a relative who was working on the
recently completed Lo Lo grade which traverses the edge of the infected area.

Of the six cases in 1928, three originated in Missoula County and three in
Ravalli. All the former were fatal. Two of them were infected in the very
dangerous O'Brien Creek section, a few miles west of Missoula. The third
was the young son of a non-commissioned officer at Fort Missoula just east
of the Bitter Root River, The source of the tick was uncertain but it is likely
that it was picked up within the limits of the military reservation. If so, it
could liave l)een one brought across the river from the nearby O'Brien Creek
country, or it may be that there has been an actual spread of infection to the
east side. A similar fatal case occurred in the same locality in 1922, the
patient claiming to have neither crossed the river to the west side nor to
have had contact with any domestic animals moved from that side. Of the
two eases definitely known to have originated from 0 'Brien Creek ticks,
one was the five-year-old child of parents who had recently arrived from
Wisconsin. The child, who was staying at an east side ranch, was ai^parently
infected by a tick brought from O'Brien Creek by one of the parents. The
other case was that of a school teacher who made a short trip into O 'Brien
Creek Canyon and was there but a few hours. Of the three recovered cases in
Ravalli County, two had been vaccinated. Of these one was extremely mild,
the otlier moderately severe. The third case, not vaccinated, was a farmer
who had been back in the mountains to turn water into an irrigation ditch.

Of the aljove 10 cases only three were persons who had resided in the
infected districts for some time. Two, possibly three, were due to ticks

(1) Contribution from the Rocky Mountain Spotted Fever Laboratory of the
U. S. Public Health Service at Hamilton, Montana.

64 SEVENTH BIEMNIAL REPORT

carried from the west to the east side of the river, two were boys who had
lived in the infected section but a few weeks, one was a person who visited an
infected country for only a few hours, and one Avas a Government inspector
who, during a period of a few weeks, made an occasional trip into dangerous
areas. Although this proportion of cases among recenl arrivals, and persons
having short or indirect contact with the infected area, is unusually high, it
serves to direct attention to the feet that many such cases occur, 50% of
those occurring during the past 12 years falling in this category.

The mortality rate in the Bitter Eoot area during the biennium concerned
(40 per cent) has been less than in recent years, presumably due in part to
the recovery of all four persons who had been vaccinated, and in part to the
fact that 60 per cent of the cases were children, among whom the mortality
rate is usually about 50 per cent. The death rate among not-vaccinated per-
sons for the past 12-year period has been 76.81 per cent of all cases, but 84.91
per cent among adults.

In addition to these naturally infected cases, four have occurred among
laboratory workers who were in contact with even more virulent strains than
those met with in nature. All were vaccinated. Three recovered, one died.

There have been no infections during 1927 and 1928 in the equally dan-
gerous but much smaller focus known as the old Eock Creek area, which
includes the southeastern corner of Missoula County and an adjoining section
of Granite County along Rock Creek.

In the remainder of the mountainous western half of Montana, there have
been but five cases, one less than during the previous two years. One was
in Gallatin, one in Jefferson, one in Lake, and two in Lewis and Clark County.
No cases occurred in Madison, Meagher, Broadwater, Mineral or Powell
Counties, from all of which infection has previously been reported.

Cases were reported from two new points in Lewis and Clark County, one
near Craig, the other near Nelson. One from Jefferson County was apparently
infected near Boulder. If so, this is also new territory, since all previous
records from this county have come from the nortliern portion near the Lewis
and Clark County line.

Spotted Fever was first reported from Lake County in 1928, Init incidental
to the securing of data relative to this case it was learned that another, which
was fatal, had been diagnosed in 1926. Both were infected in the same
general locality on Mission Creek, east of St. Ignatius.

In the half of Montana east of the Rocky Mountains there have been 49
cases and seven deaths, one more than during 1925 and 1926. Infection in
this section was unknown, except in Carbon County, prior to 1914, but begin-
ning with that year has since been reported in 23 counties involving an area
of more than 30,000 square miles. Each year infection has occurred at new
points. In 1928, a case occurred for the first time in Roosevelt County. In
counties previously known to have foci of infection, spotted fever has been
reported from new localities as follows: Near Kirby in Big Horn County,
near Mosby in Garfield County, near Clara in Golden Valley County, on Beaver
Creek in Phillips County, near Roscoe in Carbon County, south of Bundy in
Musselshell County, on West White Beaver Creek in Stillwater County, near
Hinsdale in Valley County, and from near Birney and on Armell 's Creek in
Rosebud County.

STATE BOARD OF ENTOMOLOGY 65

These data show that during the Ijieniiiuni just past, Rocky Mountain
spotted fever has continued both the intensive and extensive spread which
began in 1914.

Years in which case occurrence Avill l)e consideraljly in excess of that of
tlie jia.st few seasons are to be expected.

Table I shows the prevalence of the disease since 1911 in the areas of
highly virulent infection in Missoula, Ravalli and Granite Counties.

Table II shows similar data for other sections of the state. Besides the
1927 and 1928 cases, several other additions have been nuide to this table
since its publication in the Sixth Biennial Report. These were 1925 and 1926
cases that originated in Montana but were treated at points in Wyoming and
South Dakota. Cases originating in Carter County frequently go to Belle-
fourche, South Dakota, for medical attention. Others from southern Rosebud,
southern Powder River and southeastern Big Horn Counties go to Sheridan,
Wyoming.

Map I shoAvs in solid black the three areas of infection known in 1914 in
Missoula, Ravalli, Granite and Carbon Counties. The black dots and crosses
show the subsequent spread. Each dot and cross indicates the approximate
point of origin of one of the 352 cases that have occurred outside the three
old foci since 1914. The crosses are for cases during 1927 and 1928.

66

SEVEXTH BIEXXIAL REPORT

TABLE I

ROCKY MOUNTAIN SPOTTED FEVER CASES IN MISSOULA, RAVALLI, AND GRANITE

COUNTIES

From 1913 to 1928.

County— 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928

Missoula 35 5 1112234226313

Ravalli 87355232838 2 0333

Granite 0001000000120000

Totals 11 12 876354 11 7 11 66646

Laboratory and control work cases not tabulated have occurred as follows : 1922, 1 ; 1923, 1 ;
1924, 1 ; 1925, 1 ; 1926, 3 : 1927, 1 ; 1928, 3.

TABLE II

ROCKY MOUNTAIN SPOTTED FEVER CASES IN COUNTIES OTHER THAN MISSOULA,

RAVALLI, AND GRANITE

Beginning in 1914, the First Year that the Disease Showed a Wide Distribution Within the State.

(See footnotes 1, 2, 3 and 4.)

County-

1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928

Beaverhead ....

1

1

2

Blaine

i

1

Broadwater

1

2

i

1

6

Big Horn

2

1

1

1

1

1

3

3

"i

1

15

Carbon

2

3

'4

2

1

1

3

3

2

3

1

3

29

Carter

4

2

3

1

1

1

12

Custer

6

1

1

2

3

13

Daniels

1

1

Dawson

i

1

Fallon

2

3

i

i

"2

9

Fergus

'3

2

3

'3

7

'3

3

1

1

i

28

Gallatin

2

1

1

4

Garfield

5

i

1

i

7

11

"4

"i

3

5

1

43

Golden Valley

1

1

1

1

1

1

6

Jefferson

1

1

1

1

1

5

Lake

1

1

2

Lewis & Clark

"3

2

i

i

1

1

10

Madison

'2

i

3

McCone

2

Meagher

i

1

Mineral

1

Musselshell ....

i

"2

1

2

i

10

"i

2

i

"i

"e

43

Prairie

1

1

2

1

1

5

Phillips

3

Powell

"1

1

Powder River

"4

"2

7

Richland

i

1

Roosevelt

"1

1

Rosebud

3

1

1

■4

"s

3

'5

"'9

2

46

Stillwater

"2

1

3

2

8

Treasure

'2

1

2

1

i

"1

8

Yellowstone ..

1

1

1

9

"5

2

"2

4

"2

27

Valley

1

1

2

1

1

1

7

Wheatland ....

1

1

Totals

4

34

14

15

7

7

21

16

51

36

39

26

28

31

23

352

There are records of 17 cases in Carbon County between 1894 and 1904. None are reported

from 1905 to 1914.

In 1904 single cases were reported from each of the following counties : Fergus, Park,

Gallatin, and Beaverhead. These dia.gnoses are of doubtful reliability.

Cases imported from other states have been treated in Montana as follows : 1915, one Idaho

case in Cascade County; 1917, one Idaho case in Golden Valley County, and two Wyoming

cases in Yellowstone County ; 1921, one Nevada case in Custer County ; 1922, one Wyoming

case In Yellowstone County.

Records of Montana cases treated in other states as follows : 1915, one from Fallon County

treated in South Dakota ; 1922, one from Stillwater County treated in Wyoming ; 1923, two

from Carter County treated in South Dakota ; 1924, one from Powder River County treated

in Minnesota; one from Carter County treated in South Dakota; 1925, one from Carter

County treated in South Dakota ; 1927, one from Big Horn County and one from Treasure

County treated in Wyoming.

STATE BOARD OF ENTOMOLOGY

67

MAP I.

SHOWING DISTEIBUTION OF ROCKY MOUNTAIN SPOTTED FEVER
IN MONTANA IN 1913 AND IN 1928.

Old foci known prior to 1914:

1. Bitter Root area.

2. Rock Creek area.

3. Carbon Couutv area.

Cases outside old foci since 1913 ;
9 Points of origin of cases,

1914-1926.
+ Points of origin of cases,

1927-1928.

68 SEVENTH BIENNIAL REPORT

VACCINATION AGAINST ROCKY MOUNTAIN SPOTTED FEVERd'

By

E. E. Parker, Special Expert
United States Public Health Service

In the Sixth Biennial Eeport of the State Board of Entoniolog>', Spencer
and Parker(2) reported the results of the first two years' use (1925 and 1926)
of the Public Health Service vaccine for the prevention of Eocky Mountain
spotted fever as distinctly encouraging. Additional data secured during the
seasons of 1927 and 1928 now justify the statement that definite prophylactic
value has ben demonstrated.

Two areas have been used for test purposes ; one a small section of the
Snake Eiver valley in southern Idaho where the type of infection is the
mildest known, the other, the Bitter Eoot VaUey in Western Montana, where
the disease is prevalent in its most virulent form. The Idaho test was con-
ducted for two years, during the seasons 1926 and 1927, while in the Montana
area observations have been made during four seasons, 1925 and 1928. The
surplus of vaccine not used in these test areas has been distributed upon
request to physicians in other sections of the Eocky Mountain region, par-
ticularly in eastern Montana, Wyoming and Idaho.

The Idaho test was confined to persons handling sheep on the range
(herders, camptenders, and others). A part of these were vaccinated while
those refusing vaccination served as controls. During the two seasons con-
cerned, a single case occurred among 193 vaccinated men; this in a herder
who had refused to take more than the initial injection. Among the 364 not-
vaccinuted controls there was one case in every 16.55 men.

During the four-year period of the Bitter Eoot Valley test over two
thousand persons have been vaccinated. Part were residents of the infected
districts on the west side of the valley, and part were persons who more or
less frequently visited the danger zone. Of thirty cases of infection that
have occurred, twelve were in vaccinated and eighteen in not vaccinated per-
sons. Of the former, eleven recovered and one died. Of the latter, three recov-
ered and fifteen died. The death rate among the vaccinated persons, there-
fore, was 8.33 per cent, and among those not vaccinated 83.44 per cent.

These data indicate that the vaccine commonly confers full protection
against very mild types of spotted fever and usually sufficient protection to
insure recovery against the highly virulent types.

In parts of Montana outside the Bitter Eoot Valley area, 401 persons
have been vaccinated, most of them during 1928.

The demand for the vaccine, both from Montana and other sections of
the northwest, has been greatly in excess of the surplus that has been available
for use outside the test areas.

How Vaccine May be Secured.

The vaccine is prepared only at the Field Station of the United States
Public Health Service, at Hamilton.

(1) Contribution from the Rocky Mountain Spotted Fever Laboratory of the
United States Public Health Service at Hamilton. Montana.

(2) Spencer, R. R.. and Parker, R. R. Prophylactic Vaccination against Rocky
Mountain Spotted Fever. Montana State Board of Entomology, Sixth Bien-
nial Report, p. 29.

STATE BOARD OF ENTOMOLOGV 69

The first of the output for the season of 1929, which it is expected will
be larger than in previous years, will be available about the middle of Febru-
ary or shortly thereafter. It will be distributed directly to physicians upon
receipt of requests directed to. The Officer in Charge, U. S. Public Health
Service, Hamilton, Montana. The earlier such requests are forwarded the
more likely it is that they can be filled promptly. Each request should state
the number of persons for whom vaccine is needed.

Persons wishing to be vaccinated should make their desire known to the
physician concerned in sufficient time to allow the filing of his request for
vaccine well before the beginning of the tick season.

Full directions for administration will accompany each lot of vaccine.

A SHORT REVIEW OF THE WORK OF THE UNITED STATES

PUBLIC HEALTH SERVICE ON ROCKY MOUNTAIN

SPOTTED FEVER

By

W. F. Cogswell
Secretary, State Board of Health

On the departure of Dr. R. R. Spencer, Surgeon of the U. S. Public Health
Service, after six years ' extensive investigational work on Rocky Mountain
spotted fever in Montana, it seems to be an opportune time to briefly review
the work of the Service, as far as it pertains to Rocky Mountaiii spotted
fever, and to give expression to Montana 's appreciation of the work.

It was in 1903 that Dr. T. D. Tuttle, who was at that time State Health
Officer, requested the Service to make an investigation of a peculiar disease
which v/as then occurring in the Bitter Root Valley. Dr. John Anderson,
Surgeon,, was detailed for this work and spent the 1903 season in Montana.
In 1904 Dr C. W. Styles made an investigation for the Service. Dr. Ed-
ward Francis was sent out in 1905, and in 1906 Dr. W. W. King of the Service,
made an investigation. In 1911 Dr. T. B. McClintock and Dr. W. C. Rucker
did investigational work for the Service. All of these men did valuable work
and their reports were of value to the men who succeeded them.

For the first ten years it seemed to be the policy of the Service to detail
a different man to Montana each year to study the Rocky Mountain spotted
fever problem, but in the year 1913 this policy was changed, when Dr. L. D.
Fricks was detailed for the work. Doctor Fricks spent four successive seasons
in Montana. It was during Doctor Fricks' time that the State Board of
Entomology tick control program was worked out. This consisted in killing
the rodents on the west side of the Bitter Root Valley and adopting a plan
for the dipping of cattle. This program is still being continued. The rodents
are the hosts of the nymphs of the wood tick and cattle are the hosts of the
adult ticks.

In 1917, on account of conditions arising from the world war, the U. S.
Public Health Service discontinued its investigational work in Montana, but
in 1921, on the urgent request of the State Board of Health, the State Board
of Entomology and various civic organizations, the Service again entered the
field and since that time has done intensive work. Dr. R. R. Parker, who had
been in the employ of the State Board of Entomologj- for about five years

70 SEVENTH BIEXNIAI. REPORT

and who was thoroughly familiar with the entoinologieal end of the work, was
taken over by the Service, and in 1922 Dr. E. E. Spencer was sent out from
Washington and put in charge of the work. These men have worked together
for six years, and one of the many results of their work is the development
of the Spencer-Parker \aceine for the prevention of Eocky Mountain spotted
fever.

Montana appreciates the work of the Service in investigating this disease,
as do all of the Eocky Mountain states in which the disease occurs. This appre-
ciation was eloquently expressed by the last legislature of Montana when it
voted $60,000.00 for the construction of a proper laboratory for the Service
to conduct its work, and thus throwing around the investigators every pro-
tection possil)le against the disease.

The voluntary retirement of Doctor Spencer from active work in Mon-
tana does not mean that the work is to be discontinued. Surgeon General
Cumming visited the laboratory in August of this year, where he met the
state health officers of Minnesota, Utah, Oregon and Montana, who are all
greatly interested in the work. Assurances were given that the Service would
produce the Spencer-Parker vaccine on a much larger scale in the future and
would no doubt be able to supply the demand, not only from Montana but
from the other Eocky Mountain states.

The United States Public Health Service has aided health work in Mon-
tana in nmny other ways, and it is hoped that Congress will make adequate
appropriations so that the good work may be continued and developed more
fully.

CONTROL WORK: ROCKY MOUNTAIN SPOTTED FEVER CONTROL
DISTRICTS, BITTER ROOT VALLEY, 1927-1928

By

F. J. 0 'Don NELL

Field Agait, Montana State Board of Entomology

Spotted fever control work in Eavalli and Missoula counties for the
biennium 1927-28 has been conducted along the same general lines as were
followed in the two preceding bienniums (1923-1926) and as was reported
in the Sixth Biennial Eejiort.

The work was, therefore, confined principally to rodent control and stock
dipping, for the reason that these measures up to the present time, have
proved to be the most effective means of control.

Rodent Control Work. Rodent control work during the past two years
has been very satisfactory both as regards the acreage covered and results
obtained. The total acreage in both Eavalli and Missoula counties for the
biennium 1927-28, as shown in Table I, is somewhat less than for the pre-
ceding two-year period. This is due, in part, to the marked reduction of
rodents in certain areas in some of the control districts, thus reducing the
work required in those areas and the elimination of some other areas where
the sparse rodent population did not warrant the expenditure of the time
and money necessary to treat the land. Also, there was consideral)ly less
work done on the National Forest lands for the reason that the financial

STATE BOARD OF ENTOMOLOGY 71

assistance given to us in previous years by the Bureau of Biological Survey,
for treatment of these lands, was discontinued in 1926. Any work done on
the federal lauds the past two seasons was, therefore, done with State and
County funds, and at the expense of other areas within the control districts.
The accompanying table also shows that the expenditures for the years 1927-28
are slightly in excess of the expenditures for the preceding biennium. This is
due to a greater concentration of effort in those areas where, in the past, be-
cause of the peculiarities of the land, rocky, brushy, etc., it has been difficult to
reduce or even control the rodent population, and which serve as a reservoir for
the infestation of the adjoining lands. Thus far we have been only partially
successful in controlling these areas. Additional time and renewed effort
seem to be the required factors necessary in attaining any satisfactory degree
of success.

However, the rodent control work in the districts as a whole, has, as
above stated, been very satisfactory. The field work is well organized and
directed by competent and experienced district supervisors and we believe that
we are getting the best results obtainable by this method of spotted fever
control.

Dipping. The dipping vats in the Florence, Stevensville, Victor and Hamil-
ton districts have been repaired and filled with dipping solution and placed at
the service of the stockmen each year. The Gold Creek vat was filled in 1927, but
because of cracks in the concrete walls, the solution was diluted with ground
water and after several unsuccessful attempts to make the necessary repairs
it was decided to abandon the use of this vat until such time as title to the
vat site could be acquired by the State, and then to reline the vat with heavy
galvanized iron, similar to the lining recently built into the Stevensville, Victor
and Hamilton vats. A galvanized lining of proper weight and strength will
cost about $350.00 installed and it was thought inadvisable to expend this
amount on vat as the site was not State-owned land.

During the summer of 1927, an attempt was made to acquire title to
the Gold Creek vat site, but at that time the land on which it was located was
in litigation and a good title could not, therefore, be secured. Dipping during
1927-28 was not as satisfactory as during the preceding two years, that is,
the number of stock dipped was somewhat less, due to unfavorable weather
during the dipping season. This condition could be remedied to a great extent
if, as has been emphasized in previous reports, there were a sufficient num-
ber of vats so located that it would not be necessary to drive stock long dis-
tances and also in stormy weather stockmen would take advantage of the
occasional clear days if the vats were more conveniently accessible.

Stock Poisoning. During the active rodent poisoning each year, com-
plaints are frequently made to either the field men or direct to the station
concerning the death of range stock and farm animals which have died allegedly
as a result of eating rodent poison distributed by agents of this department.

During the past five years thirty-four such complaints were received at
the Station as follows:

1924 10 1925 4 1926 6

1927 8 1928 6

In each instance an investigation was made immediately and when possible,
and circumstances warranted, a specimen of stomach contents was procured and

SE\'EXTH BIEXXIAL REPORT

gag

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STATE BOARD OF ENTOMOLOGY 73

sent to Dr. Emil Starz, Chemist, Live Stock Sanitary Board, Helena, with a
request that it be tested for strychnine, which is the active ingredient in our
grain poison. When the test was positive for strychnine and other circum-
stances indicated that the animal had eateu rodent poison distributed by agents
of this department, and through no fault of the owner of the animal, then set-
tlement was usually made, based on the assessed valuation of the animal. Of
the ten complaints received in 1924, two were of cattle poisoning which oc-
curred iu 1923. One, a case of three heifers which had strayed into and were
trapped in the Stevensville vat corrals, where they probably got some arsenic.
The other was a case of three head of dairy stock which were killed probably
as a result of eating rodent poison. In both of these cases settlement was
made, the former for $45.00 and the latter for $.50.00, or a total of $95.00. In
only four of the remaining eight cases did it seem likely that the animals died
of rodent poison. These four cases involved five horses and seven i)igs and
settlement was made for $210.00, or a total of $305.00 for 1924.

The four complaints in 1925 included nine sheep, two cows, two pigs and
four geese, and settlement was made for $270.00.

Of the six cases reported in 1926, which involved 5 cows and two horses,
none was due to rodent poison and iu only one of the four cases reported in
1927 did circumstances justify payment for the animal, a horse, for which
settlement was made for $25.00.

None of the cases reported in 1928 indicated rodent poison as the cause
of death.

We therefore made settlement in only one case and for only one animal
during the past three years, at a total cost of $25.00, as compared with settle-
ment made in ten cases involving 19 animals and 4 geese, at a total cost of
$575.00 for the preceding two years.

This marked reduction in the loss of range stock, farm animals and poul-
try incident to the distribution of rodent poison is due principally to a change
in the method of placing the squirrel baits at or near the squirrel burrow.
Up to and including 1925 the bait (about a teaspoonful) was placed at the
side or on the mound to the rear of the burrow in a small pile. This method
of placing the bait made it possible for a farm animal to more easily get the
poison in amounts sufficient to cause death. For the past three seasons we
have been using the same amount of poisoned grain per bait, but it is scattered
over an area eight or ten inches square, thus making it difficult for an animal
to procure a lethal dosage of poison without also picking up sand, soil, etc., in
the attempt to get the grain.

Another factor in the decrease of the loss of stock from rodent poison
is the use of calcium cyanide in pastures, particularly hog and sheep pas-
tures, A%here it is not always convenient to remove the stock while the land is
being treated and also the use of this material near farm dwellings where grain
fed animals, and geese and ducks, are more likely to get at the grain poison.
The calcium cyanide is placed into the burrow and where deemed necessary the
burrow is closed with a shovelful of earth, thus all danger to stock, geese,
ducks, etc., is entirely eliminated.

Cooperation of the counties concerned has been very encouraging. We
have had the moral support as well as such financial assistance as was re-
quested from the Commissioners of the respective counties. Eavalli County

74 SEVENTH BIEXNIAL, REPORT

has each year appropriated $3,000.00 and Missoula County has given $2,000.00
each year to be expended for rodent control work under the direct supervision
of the Board of Entomology.

Our dealings with the Commissioners and other officials of both Missoula
and Eavalli Counties have, as in the past, been very satisfactory. These offi-
cials have always shown a keen interest in the work and have assisted in every
way possible.

Acknowledgment is also made of the cooperation and assistance of the
Live Stock Sanitary Board, and especially Dr. Emil Starz, for the laboratory
work done for this station during the past two years.

Occurrence of Spotted Fever Within the Older Control Districts in
Ravalli County — 1913 to 1928 Inclusive.

The accompanying graph has been prepared for the purpose of showing
the incidence of spotted fever within the boundaries of the older control dis-
tricts in Ravalli County from 1913 to 1928, inclusive. Actual control work
was first begun in a small area west of Victor by McClintic of the United
States Public Health Service in 1911, and 1913 by King of the Federal Bureau
of Entomology in an area Avest of Eloreuce.

These Federal Bureaus gradually extended the control work until 1917,
when all of the territory between the Missoula-Ravalli County line on the north
to Lost Horse Creek on the south, was included within the boundaries of the
control districts. From 1913 to 1917 the Board of Entomology acted in a co-
operative capacity only. At the close of the season of 1917 both Federal
agencies were obliged to withdraw from the field.

In the spring of 1918 the Board took charge of the work and since that
time has had full supervision. Under the direction of the Board additional
area was included in the districts and new districts created, until now the con-
trol aroa includes all of the territory from Burnt Ridge south of Darby to the
Big Flat north of Missoula, a distance of about 69 miles, varying in width
from 3 to 7 miles and embracing an area of 212,180 acres on which active
control work is done.

The graph, however, shows only those cases which have occurred in the
Florence, Stevensville, Victor, Hamilton and Gold Creek districts, as the con-
trol work has been more or less continuous over the greater portion of this area
since 1913. The districts south of Gold Creek and north of Florence were
created subsequent to 1921. It will be noted that there has been a total of
49 cases during the 16-year period covered by the graph, or a rate of 3.06 cases
per year, also it will be noted that there is a downward trend in the curve
and that for the past three years there have been only two cases per year. To
what extent the control work is responsible for the decrease in the incidence
of the disease is a matter of conjecture. There are several other factors
which probably have more or less influence in controlling the disease, as for
instance the circular letter outlining the season 's control program which is each
spring addressed to every resident in the control districts and a short time later
the appearance of the rodent crews in the field, no doubt serve, to some extent
at least, as a seasonal reminder, and to emphasize the potential danger from
ticks and tick-infested areas. Another factor is the relatively large number

STATE BOARD OF ENTOMOLOGY

75

of persons living iu the control districts who have received the Spencer-Parker
vaccine during the past three years. It is evident, however, that much good
has been accomplished by the control work. The great reduction in rodents
over large areas and the resultant and very apparent decrease of ticks in these
areas fully justify the expenditures of money and effort necessary to properly
carry on the control program.

SEVENTH BIENNIAL REPORT

TULARAEMIA AND TICK PARALYSIS

INTRODUCTION

In the Sixth Biennial report a general account of tularaemia and a state-
ment of what is known of its occurrence in Montana was presented in a paper
by Dr. E. E. Parker of the Public Health Service. The first evidence that this
disease was prevalent in the State was the recovery of infection from specimens
of Dermacentor andersoni which were being tested for the presence of the virus
of Eocky Mountain spotted fever at the Field Station of the Public Health
Service at Hamilton, in 1923. Thig led to the demonstration by the local staff
of that service that the wood tick is a frequent carrier of this disease. In the
above noted paper, Dr. Parker gives an account. (1) of how it is transmitted
to man, (2) of how the disease is presumably maintained in nature among
our native species of rodents (at least eleven of which are known to be sus-
ceptible, (3) of its then known distribution in the State and (4) of 55 cases
which were reported in 1925 and 1926 from Garfield, Custer, Powder Eiver,
Eosebud, Musselshell, Fallon, Dawson, Yellowstone, Gallatin and Madison
Counties.

Dr. Parker advises that since the sixth report, sixteen additional cases
have been reported, nine in 1927, five in 1928, and one each for 1924 and 1925,
the diagnosis of the last two having been made by means of agglutination tests.

Of the 1927 and 1928 cases, oiie was in Fallon County, two in Yellowstone,
one in Powder Eiver, one in Garfield, one in Dawson, one in Fergus, one in
Eosebud, one in Lewis and Clark, two in Silver Bow, one in Custer and two in
Broadwater. The 1924 ease was in Flathead County, and the 1925 in Garfield.
In addition to these instances of human infection, ticks infected with tula-
raemia were collected near Menard, Gallatin County, in June, 1928, by members
of the staff of the State Board of Entomology.

In the paper which follows, Drs. Parker and Butler give the results of
preliminary investigations which they have made in Montana of pathological
conditions in sheep following wood tick bites. Their data, secured in 1923
and 1925, suggest that tularaemia may have been responsible, at least in part,
for the losses that have been incurred.

STATE BOARD OF ENTOMOLOGY 77

RESULTS OF PRELIMINARY INVESTIGATIONS IN MONTANA OF

PATHOLOGICAL CONDITIONS IN SHEEP DUE TO THE

WOOD TICK, DERMACENTOR ANDERSONI STILES'D

By

E. E. Parker, Special Expert, U. S. Public Health Service,

and

W. J. BuTLRR, State Veterinary Surgeon of Montana.

Hadwen's description in 1914 of tick paralysis in sheep in British
Columbia2 was the first evidence of pathology in sheep resulting from the
bite of the wood tick, Dermacentor andersoni Stiles. This condition has
since been observed in the same region by Bruce,^'* but until 1923 there
was no evidence of suspected wood tick-caused disease in sheep from any
other section within the range of this tick. In the spring of that year, losses
attributed to B. andersoni were reported from both eastern Montana and south-
ern Idaho. This resulted in an arrangement between the Field Station of the
U. S. Public Health Service at Hamilton, Montana, on the one hand, and Doc-
tors W. J. Butler and James Dade, respectively the State veterinary surgeon
of Montana and the ehief inspector of the Idaho State Sheep Commission, on
the other, for the comparative study of future outbreaks in their respective
states.

The results of the studies with Dade indicate that tularaemia infected
ticks have been largely, possibly wholly, responsible for the southern Idaho
trouble. On account of these studies (Parker and Dade) either has recently
appeared in the Public Health Eeports.

The details of the Montana observations are incorporated in the present
paper. Unfortunately, the results have been less definite than those secured
in Idaho. This has been due to the very incidental character of the field ob-
servations and the lack of opportunity to make bacteriological examination
of the tissues of affected animals. It seems probable, however, that similar
conditions have been of more frequent and widespread occurrence than present
data show, and it is hoped that the publications of this preliminary data will
stimulate more careful observation and reporting by sheep owners of disease
conditions that occur in wood tick areas shortly after sheep are placed on the
spring range. There is apparently a feeling among many owners that a certain
percentage of loss is to be expected, and, unless it is unusually heavy, there
is no desire to ascertain the cause.

(1) Contribution from the Rocky Mountain Spotted Fever Laboratory of the
U. S. Public Health Service at HamilTon, Montana, and the office of the
State Veterinary Surseon at Helena Montana.

(2) Hadwen, Seymour. On "Tick Paralysis" in Sheep and Man following Bites
of Dermacentor venustus; with Xotes on the Bio.ogy of the Tick. Parasit-
ology, Vol. 6. pp. 28.3-287. 1914.

(3) Bruce, E. A. Tick Paralysis in British Columbia. Health of Animals Branch,
Can. Dept. Agr. Bull. No. 28, 1920.

(4) Bruce. E. A. Tick Paralysis. Jour. Amer. Vet. Med. Assoc, Vol. 48, N. S. 21,
No. 2, Nov. 1925.

78 SEVENTH BIEXXIAL, REPORT

The field observations herein reported were made almost entirely by Doctor
A. F. Baldwin of Miles City, local deputy for the Montana Livestock Sanitary
Board; neither of the writers being able to visit any of the affected bands
during the acute stage of the trouble.

G. P. Pone Band, 1923.

(Near Miles City, Custer County.)

On April 30, Doctor Baldwin was called to investigate deaths of yearling
sheep in four bands belonging to G. B. Pope of Miles City. The owner at-
tributed his losses to "poison weeds." Doctor Baldwin reported that affected
sheep tended to walk "in circles to right or left" would "stagger and fall"
and were unable to rise. He noted that the affected animals were infested
with wood ticks and removed the larger ones (i. e., the engorged females) from
several of them, not, however, supposing that these ticks were in any way con-
cerned with the condition of the sheep. Much to his surprise, when he again
visited these same sheep a few hours later, those from which the ticks had
been removed were on their feet^ while the others were still ' ' down. ' ' The en-
gorged females were therefore picked from the latter with the same result as
before. This experience appeared to justify a diagnosis of "tick paralysis"
and was the first suggestion of the possible occurrence of this condition in-
Montana. Dead jackrabbits were noted in the locality in which the affected
bands were being grazed.

The total loss of sheep in the four bands exceeded 100 head, the heaviest
loss being 75 yearlings of a band of 3,800 which had recently been shipped
in from Big Timber. In each of the other three smaller bands, about 50 year-
lings and ewes were affected.

Trumball and Taudy Band, 1923.

(Near Miles City.)

On May 5, a few days after visiting the Pope band, Doctor Baldwin was
called to see the Trumball and Taudy band, which was found similarly af-
fected, except that in addition the sick ewes were aborting their lambs. The
sheep co]icerned had just been shipped in from Ekalaka (Carter County) and
Ismay (Custer County), reaching Miles City on May 3. A number of sheep
were down and unable to rise. In his inspection report. Doctor Baldwin stated
that "the sheep from which all large ticks (engorged females) were removed
made recovery. On those that died, other large ticks were found that had been
missed on the first examination. The ticks were attached under the jaw and
on the neck, belly and legs." These further observations seemed to strengthen
the idea of tick paralysis. The dying of rabbits was reported from the sec-
tion of Custer County from which part of the sheep had been shipj^ed.

Several ticks from affected sheep of this band were sent to the Hamilton
laboratory. Five partially engorged females were emulsified in salt solution
and each inoculated intraperitoneally into a guinea pig in the same manner
as in routine tests which were being made for Eocky Mountain Spotted Fever
in fed ticks^.

All five guinea pigs died, two in 3 days, two in 6 days, and one in 7 days.
Four were afebrile, but the temperature of one reached 41.0 °C. The gross
pathology as noted at necropsy was not specifically suggestive, and because

(5) Spencer, R. R. and Parker, R. R.; Rocky Mountain Spotted Fever: Inf activity
of Fasting- and Recently Fed Ticks. Pub. Health Rpts., Vol. 38, No. 8,
pp. 333-339, Feb. 23, 1923.

STATE BOARD OF ENTOMOLOGY 79

the circumstantial evidence so strongly suggested tick paralysis, the tests were
not carried further. Later in the season, after the demonstration of the preva-
lence of tularaemia-infected wood ticks in nature and of the transmissability
of Bacterium tulareiise by D. anclersoni,^ the above tests were recalled. They
were entirely comparable to many subsequent tests of known tularaemia-in-
fected ticks and this fact coupled with the knowledge of the dying off of jack-
rabbits in localities where the bands became affected makes it seem almost a
certainty that the guinea pigs died of acute tularaemia. Had tissue transfers
been made to other guinea pigs as in subsequent tests (see 1925 data below) it
is felt that typical lesions would have resulted.

Danford Band, 1925.

(Near Calabar, Custer County)

The same condition as observed in 1923, was again met with by Doctor
Baldwin in the Danford band, during lambing in early April, 1925. A high
percentage of the band had been affected, and according to Doctor Baldwin,
the sheep "act peculiar," stagger around, go down, and abort their lambs.
Ticks collected April 10 from two ewes that were "down" and had aborted
were received at the Hamilton Field Station April 13. These ewes had been
left behind the band at the outskirts of Miles City. Five groups of ticks,
each consisting of two partly engorged females, were emulsified in salt solu-
tion and injected intraperitoneally into five guinea pigs. Four of these five
tests were positive for tularaemia, the fifth was terminated by intercurrent
infection.

Guinea Pig 1 died in five days; the spleen was slightly suggestive of tula-
raemia and transfer by spleen emulsion was made intraperitoneally to two
guinea pigs, one of which died in three days, the other in seven. The gross
lesions were typical in both.

Guinea Pig 2 died in six days with typical lesions of tularaemia. A spleen
emulsion inoculated into two guinea pigs also caused typical death, respectively,
in four and five days.

Guinea Pigs 3 and 4 remained apparently well and were killed and autop-
sied 13 days after inoculation. Both showed no lesions other than slightly en-
larged spleens. The spleen of Guinea Pig 3 was transferred by salt solution
emulsion to a second guinea pig which died in 8 days with suggestive lesions.
Transfer to a third guinea pig caused death of typical tularaemia in 8 days.
The spleen of Guinea Pig 4 was similarly transferred through a series of three
additional guinea pigs. There was necrosis of spleen and lungs in the third
guinea pig which died four days after inoculation. The fourth also died in
four days with typical lesions of spleen, liver and glands.

Guinea Pig 5 died 13 days after inoculation. Necropsy showed evidence
of intercurrent infection, and no transfer was made.

S^viim was collected from one of the aljove ewes April 27, 17 days later
than the removal of the ticks, both ewes having recovered in the meantime.
This serum agglutinated Bacterium tularense in all dilutions up to and in-
cluding 1:640.

(6) Parker R. R., Spencer, R. R., and Francis. Edward. Tularaemia Infection in
Ticks of the Species Dermacentor andersoni Stiles in the Bitter Root Valley,
Montana. Pub. Health Rpts., Vol. 39, No. 19, pp. 1U57-1073, May 9. 1924.

80 SEVENTH BIENNIAL REPORT

The spleen of one of the transfer guinea pigs from Guinea Pig 2 was for-
warded to Surgeon Edward Francis at the Hygienic laboratory at Washing-
ton, and with it he infected guinea pigs from which Bacterium tularense was
recovered in pure culture. This culture was agglutinated by the immune
serum of a rabbit which had been immunized against a culture of B. tularense
recovered from a human case in Utah by Doctor Francis in 1920.

Cusick Band, 1925.

(Near Powderville, Powder River County.)

In the spring of 1925 the Cusick band of 1,570 sheep was being ranged on
Stump creek, a few miles east of Powderville and about 70 miles south of Miles
City. These sheep had been dipped in the fall, had wintered in unusually good
condition, and were free of sheep ticks (Melophagus ovinus). They remained
in fine shape until they became heavily infested with wood ticks in late March,
after which the whole band lost condition. One ewe was "down" April 1,
tAvo Ai)ril 2, three April 3, five April 4 and ten April 5. On this date the
owner came to Doctor Baldwin for advice and was told to look for and re-
move engorged wood ticks. Doctor Baldwin visited the band April 17, on
which date he found that over a hundred head had been down, but that after
removal of the engorged females all had recovered except seven of the original
ten, from which the ticks had not been removed until after they had been down
several days. Tick infestation was heavy, some sheep having more than a
hundred. They were attached to the legs, belly, neck, around the base of ears,
above the eyes, and on top of the head. Many dead jackrabbits were seen and
many sick ones that were heavily infested with ticks.

Ticks were secured from three ewes, A, B and C, two of which, B and C,
were "down," the third recovered. A blood sample was also taken from the
recovered ewe, A. This material was forwarded to the Hamilton Field Station
and was received April 23.

On May 11, one of the writers, Butler, accompanied Doctor Baldwin on
a second visit to the band. Blood samples were secured from three more ewes,
D, E {aid F, as well as ticks from one of them, ewe D. All were reported as
recovered animals. A third visit was attempted in late May by Butler, Baldwin
and Parker, but impassable creeks, due to high water, prevented reaching the
band.

Most of the engorged and partly engorged females collected on April 17
and May 11, from the four ewes, A. B. C and D, were tested for tularaemia
infection. Seven guinea pigs were inoculated siibcutaneously with two par-
tially engorged females each; 21 partially fed females were fed on four other
guinea pigs and of the females that thus completed engorgement, six were fur-
ther tested by inoculating them separately and three by inoculating their eggs ;
14 engorged females recovered directly from the ewes were kept for egg deposi-
tion and after this was well advanced, nine were tested by injecting them sub-
ciitaneously into guinea pigs and five by the injection of their eggs. The four
sera from ewes A, D, E and F were tested for ability to agglutinate B. tula-
revse.

The results of the tick inoculations showed that of a minimum of five
tularaemia -infected ticks, three were from ewe B and two from ewe C. The
number of ticks actually infected was unquestionably considerable in excess of
five, but many of the tests which resulted in suggestive lesions in the initial

STATE BOARD OF EXTOIMOLOGY 81

lest animals were uot completed because of disorgauization of the station staff
by laboratory acquired tularaemia infections. The four sera from the sup-
posedly recovered ewes (A, D, E and F) all failed to agglutinate B. tularense,
but unfortunately none of the samples were from the acutely ill ewes B and C,
from wliich tlie definitely tularaemia infected ticks Avere recovered.

Tlie aliovo test results are not of direct significance as regards the re-
sponsibility or lack of responsibility of tularaemia-infected ticks for the con-
dition in the Cusick band. The typically positive tests will be detailed, how-
ever, both because they were of value as showing that tularaemia infection
was present in ticks infesting affected sheep, and because they illustrate so
well the advisaljility of not ascribing definite tularaemia-negative significance
to apparent tularaemia-negative pathology in guinea pigs injected with sus-
pected infection bearing material.

Ewe B.

Emjoriied Female from Eive. Kept for egg deposition, and on May 7
when this was nearly complete, tick was emulsified in salt solution and in-
jected intraperitoneally into Guinea Pig 1. The latter was dead May 20.
Necropsy showed enlarged spleen, enlarged and haemorrhagic inguinals and a
suggestive lung condition. A transfer by lung emulsion caused the death of
Guinea Pig 2 on May 29. Autopsy showed typical tularaemia lesions of spleen
liver and glands.

Engorged Female from Ewe. Inoculated intraperitoneally April 25, into
Guinea Pig 2. The later was apparently well when killed and autopsied May
8. The only gross pathology was a slightly enlarged spleen and several -small
grayish white necrotic foci in the fatty tissue at the distal poles of the testes.
Transfer by spleen-polar fat emulsion was made to Guinea Pig 3, which was
dead May 20. Inguinal glands were slightly enlarged and haemmorrhagic,
spleen was four times enlarged with a few scattered foci of necrosis, liver
]iathological but not macroseopically necrotic and was adherent to the stomach.
Spleen emulsion transfer to Guinea Pig 4 caused death of the latter May 23.
There was a generalized lung involveiiiont and spleen two times enlarged.
Guinea Pig 5 was injected with a spken emulsion and died May 26. The spleen
emulsion transfer to Guinea Pig 6 resulted in a typical recognized tularaemia
infection, the guinea pig dying May 31, and showing ulceration at site of in-
oculation, caseous inguinal bul)oes, enlarged caseous pelvics and retrosternals,
spleen five times enlarged, and it and liver typically necrotic.

Partially engorged Females that were refed. Nine partially fed females
from ewe B were placed on a guinea pig for feeding April 28, and removed
May 7. Five had completed engorgement, and three had fed little, if at all.
The host guinea pig died afebrile May 9, with indefinite lesions and was not
transferred.

The three partially engorged ticks were immediately inoculated intra-
peritoneally into a guinea pig which died May 20. The spleen was three times
enlarged, the inguinals enlarged and the right haemorrhagic. Transfer by
spleen emulsion to a second guinea pig caused the latter 's death May 31 of
typical tularaemia. There was ulceration of site in inoculation, consolidation
and necrosis of the lungs, spleen and liver were typically necrotic, and re-
trosternal and pelvic glands were enlarged and caseous and the retropancreatic
enlarged. Of the five fully engorged females four were tested May 16, egg

82 SEVENTH BIEXXIAL RErORT

deposition being nearly complete, by injection into guinea pigs, and one by
inoculation of its eggs. One of the guinea pigs that received tick viscera av;is
dead May 25, The spleen was but slightly enlarged and of iionual color; the
omentum contained grayish white necrotic foci and there was a serous peritoni-
tis. Transfer by an omentum emulsion was made subcutaneously to a second
guinea pig which died typically on May 31.

• The above tests showed at least three ticks from ewe B to have been in-
fected with B. tularense. Although four tests were definitely positive, the pos-
sibility cannot be excluded that one of the two refed ticks may not have ac-
quired infection through the medium of tlie guinea pig on which they both fed.
Definite infection was not recovered from any of the companion ticks, how-
ever, but this may have been because transfers were not made from the initial
test animals.

Ewe C.

Partially engorged Females that were refed. On April 28, four slightly
to one-third engorged females were placed on a guinea pig, which was dead
May 4, but without typical pathology. From this guinea pig a series of five
transfers were made. The test animals for the second and subsequent trans-
fers all died of typical tularaemia. The spleen of the second transfer guinea
pig, preserved in glycerine, was forwarded to Francis and from it he infected
four guinea pigs from one of which he recovered a pure culture of B. tula-
rense. This was agglutinated by a 1 : 1280 dilution of the same immune
serum previously used.

All the ticks recovered from the above guinea pig were injected into a
second, which died May 17 with very slightly enlarged spleen, injected in-
guinals and evidence of pneumonia. It is of interest to record that in spite
of a series of three transfers typical diagnostic lesions were not produced,
although one or more of these ticks had been responsible for the infection of
their host. The lesions in each of the three transfer animals were suggestive,
however, and a note was made to the effect that had transfers been continued
typical lesions might have resulted.

Partially fed Females that were refed on a Yearling Sheep. On April 28,
25 ticks were placed on a yearling ewe purchased locally. This sheep had al-
ways been pastured under fence in a tick-free country. Thirteen days later,
on May 11, eleven fully engorged females were recovered and were inoculated
in five guinea pigs, four receiving two ticks each and one three ticks. Two
test animals died respectively May 15 and May 16 with indefinite lesions.
Tissue transfers from both resulted in typical tularaemia infections. The
other three initial test animals showed equally suggestive lesions, but were not
transferred.

Samples of serum secured from the yearling host on May 12 and 19, re-
spectively 14 and 21 days after infesting it with ticks, both failed to agglu-
tinate B. tularense.

The data of the above tests show tliat at least one of the four ticks fed
on the guinea pig and at least one of those fed on tlie sheep, were infected.

Summary of Test Data for Cusick Band.

The material received from the Cusick band consisted of four lots of
ticks from four ewes and four samples of sera.

STATE BOARD OF ENTOMOLOGY 83

Two of these lots of ticks were collected from supposedly recovered ewes,
two from ewes actually ill- All four samples of sera were from recovered
animals.

Of 16 ticks tested from the two recovered ewes none were shown definitely
to be infected with tularaemia. However, several initial test guinea pigs
showed necrosis of liver or spleen or suggestive lesions of other tissues, and
had tissue transfers been made it is probable that several positive tests for
tularaemia would have resulted.

Of fifty ticks tested from two acutely affected ewes a minimum of five,
i. e., at least 10 per cent, were shown infected with B. tularense, three from
one ewe, two from tlie other. That the actual number of tularaemia-infected
ticks was greater is very probable.

None of the four seia from supposedly recovered animals agglutinated
B. tidareuse.

Barley Bros. Bands.

(Northicest of Miles City, Custer County)

On April 21, Doctor Baldwin was called to see affected sheep of a band
belonging to Barley Bros., on Sand Creek, 25 miles northwest of Miles City.
A band of 1500 yearlings which were ranging on the East Fork of Sand Creek
had become heavily infested soon after going on the range. Symptoms were
noted in the sheep in early April but the herder thought them due to eating
poisonous weeds. However, in a few days so many sheep were sick that he
went to headquarters for help.

When the band was visited by Doctor Baldwin April 21, a hundred sheep
had been down, 25 had died and many others had been affected to greater
or less degree. Hides recently moved from sheep that had died showed ' ' many
dark haemorrhagic" spots where ticks had been attached.

The band was again visited May 11 by Doctors Butler and Baldwin.
Fourteen engorged and four partly fed females and six males were taken
from a sheep that w^as down. This sheep was reported to have been down
before, but had recovered after removal of the wood ticks and the soaking
of points of attachment with dip. Ten of the above ticks were tested in the
same manner as before. One of the engorged females caused suggestive
lesions in the initial test animal and spleen emulsion transfer to a second
guinea pig caused death of typical tularaemia. In guinea pigs representing
three other tests necrosis and other suggestive lesions were present. For
example, one of the autopsy records reads as follows: "Lungs typically necro-
tic; spleen four times enlarged, both it and liver suspicious."

During the period that the above baud was affected another was being
grazed within a fenced area in which no stock had been grazed for several
years and ticks were few. Xo trouble was experienced, but later on, after
removal to open tick infested range on Coal Creek, this band also was se-
verely affected. The loss amounted to 60 yearlings and 40 ewes.

Dead jack and cottontail rabbits were extremely numerous on both ranges
concerned.

In 1926 ticks were again numerous in the areas concerned but no trouble
was experienced. However, one of the owners, J. Barley, liimself became in-
fected from tick bites, the specific character of his illnesj being verified by
an agglutination test.

S4 SKVEXTH BIEXXIAI. REPORT

Eesult. Of teu ticks tested from a yearling down for the second time,
one was definitely shown infected and suggestive lesions were caused by sev-
eral others.

Discussion.

There seems to be no reasonable doubt of the initiating part played by the
tick, B. andersoni, in the disease outbreaks in sheep reported above, but the
relative extent to which tick paralysis and tularaemia are to be blamed for
the resultant pathology is less clear. The possibility that some third tick-
caused condition may occur in sheep cannot be denied, but if such exists there
is no evidence to suggest it in the data thus far secured.

The possibility that tick paralysis may have been concerned rests solely
on Doctor Baldwin's observations as to actions of affected sheep and their
more or less rapid recovery providing infesting female ticks were removed
soon after symptoms were noted.

Eelative to the possible responsil)ility of tularaemia there is more data,
but, except in the case of the two Danford ewes, it is entirely circumstantial
and does not justify any opinion as to the extent to which B. tularerise may
have been involved. Although the writers feel that tularaemia infected ticks
were undoubtedly present on affected sheep at the time of the 1923 trouble
there is no incontrovertible evidence to this effect. For that matter, there
was at the time no knowledge that tularaemia infection was present in the
state, nor was it until later that season that the Public Health Service began
experinionts which resulted in demonstrating the part played by B. andersoni
in its dissemination. However, judging from our present knowledge, it seems
highly probable that the death of jack rabbits, which was reported coinci-
dent with the trouble in sheep in the areas concerned, was due to this disease.
If this hypothesis be correct, our present knowledge would then justify the
assumption that tularaemia infection must have been present in ticks; and,
as has previously been noted, it is now felt that the death of the five guinea
pigs, each injected with a single female tick taken from affected sheep of
the Trumball and Taudy band, was caused hy this infection. While this is
not susceptible to proof, yet the familiarity of one of us (Parker) with the
results of injecting thousands of wild wood ticks into laboratory animals
justifies at least the conclusion that some infectious agent was responsible
Furthermore, the fact that all five ticks, which were selected indiseriminatelv
froju those received, caused death, suggests that part of them at least may
have acquired this infectious agent from the sheep on which they were feed-
ing. That so high a jjercentage of unfed ticks similarly selected at random
should be infected with disease organisms is extremely unlikely.

In 1925, tularaemia infected ticks were recovered from affected sheep
of each of the three bands concerned. This fact alone, however, lacks sig-
nificance because, as reported by Parker/ we know that tularaemia was quite
prevalent that year in ticks, in rabbits and other rodents, and in man in the
part of eastern Montana concerned, and it is certain that infection could have
been recovered equally well from unfed wood ticks collected from the sage-
brush. In other words, though we know that sick sheep were infested with
an agent infected with, and capable of transmitting, B. tularense, we never-

(7) Parker, R. R. Tularaemia and its occurrence In Montana. Mont. State
Board of Entomology, Sixth Biennial Report, pp. 30-41, January, 1927.

STATE BOARD OP ENTOMOLOGY 85

theless have no actual evidence to show that such transmission really occurred.
However, in the case of the two Danford ewes that aborted, we do have the
additioual evidence that the serum of one of them, secured after recovery,
agglutinated B. tularense in dilution of 1 : 640. Turthermore, as in the case
of the Trumball and Tandy band in 1923, so high a percentage of the infest-
ing ticks were found to be infected with tularaemia that it seems probable
that part of them may have become infected from the sheep on which
they were feeding. However, this one positive agglutination test would mean
little, were it not for the results of the Idaho tests, in the spring of 1928.8 We
feel that these combined data justify the opinion that in this instance B. tula-
rense was the specific disease factor concerned. On the other hand, we do not
feel that even the Idaho data warrants any assumption as to the extent to which
tularaemia may have been responsible for the trouble in the other eastern
Montana bands. For example, although tularaemia infected ticks were re-
covered from sheep of the Cusick band, sera of four supposedly recovered
ewes failed to agglutinate B. tularense even in low dilutions. Furthermore,
the symptoms as observed by Doctor Baldwin in the affected eastern Montana
bands do not agree with those observed by Dade in southern Idaho. Therefore,
although the evidence for the Danford ewes suggests that tularaemia-infected
ticks were at least in part responsible for the trouble in that particular band,
there is nothing but circumstantial evidence of doubtful value on which to
base any more inclusive opinion.

The lack of critical and differential data on which to base any definite
conclusion is due to insufficiently complete field observations of affected
bands and failure to determine whether or not B. tularense were present in
the tissues of animals acutely ill or recently dead. These deficiencies can
readily be supplied in case of future outbreaks. Satisfactory field data, how-
ever, will require the observation of affected bands for several days or longer
and, in addition, a considerable number of the affected animals should be
isolated for detailed observations which should be correlated with bacteriolog-
ical and serological laboratory studies.

The possibility has been considered that tick paralysis and tularaemia
in sheep may be one and the same condition. While this should be borne
in mind, present evidence is admittedly against it.

iS) See introductory part of this paper.

Seventh biexntAl report

MONTANA'S LABORATORY FOR THE STUDY OF
INSECT-BORNE DISEASES

E. A. COOLEY

Secretary, Montana State Board of Entomology.

Probably tliere does not exist another research laboratory like the one
of the Montana State Board of Entomology which has recently been com-
pleted at Hamilton. The field of work as laid down in the Act which created
this Board in the year 1913, is "to investigate and study the dissemination
by insects of diseases among persons and animals, said investigation having
for its purpose the eradication and prevention of such diseases," and the
new laboratory is designed and equipped, so far as is possible within the
available fund, to perform the necessary studies connected with insect-borne
diseases. The Act authorizing the erection of this Laboratory, signed by
Governor Erickson on March 16, 1927, appropriated the sum of $60,000. The
building is a brick faced, reinforced concrete structure of three stories, 40
feet by 66 feet on the ground. A one-story wing 88 feet in length is attached
to the west and is designed for the care of stock laboratory animals. The
building is made without a liasenient in order that it may be as sanitary as
possible, and to have as few places as possible where insects or rodents may
hide away. The construction throughout is such as to avoid cracks and sharp
corners. The boiler burns oil and is automatic and certain of the rooms have
automatically controlled temperatures. While the building is planned gen-
erally for the field of medical entomology, and closely associated lines, it is
laid out particularly for the needs immediately before the state. The common
wood tick of the region, Dermacentor andersoni Stiles, and the diseases of
man and the losses in livestock of which it is the cause, constitute the imme-
diate problem.

The work on Eocky Mountain Spotted Fever is being conducted under
an informal plan of co-operation between the U. S. Public Health Service
and the Montana State Board of Entomology. At the present time the U. S.
Public Health Service is concerned mainly with a further study of the Spencer-
Parker vaccine. This vaccine, made from the bodies of infected ticks, was
originated two years ago at the old, improvised laboratory at Hamilton and
at the Hygienic Laboratory at Washington, D. C, by the two U. S. Public
Health Service workers whose name it bears. It now has been used on about
4,000 persons in Montana, Idaho and Wyoming, with uniformly encouraging
results.

A feature of the Spotted Fever studies in Montana is that they are
planned and carried out with careful reference to field conditions. It is for
this reason that the new laboratory was erected at Hamilton in close proximity
to regions where Eocky Mountain Spotted Fever is found. Field conditions
may be thus easily studied, materials for study may be brought in, and para-
sites may be bred and quickly liberated.

STATE BOARD OF ENTOMOLOGY 87

Laboratory work on Spotted Fever has always been dangerous for the
workers. Up to the time that the Speneer-Parker vaccine was developed there
had been 4 cases of laboratory infection with the disease in Montana (3 at
the field laboratories and 1 in Helena). All of these cases were fatal. Since
we have had the vaccine there have been 7 laboratory cases and 6 of these
have recovered. It is now indicated that the vaccine gives full protection
against all strains of the disease excepting the more virulent one in the region
near the laboratory, and sufficient protection in the majority of cases to
insure recovery from infection with the more virulent strains. It is hoped
the new laboratory with its modern conveniences will afford much better
protection for the workers than was possible in the one being abandoned
which was a vacated schoolhouse.

The new building provides an incinerator for the disposal of dead animals
and all waste ; a specially adapted laundry and drying equipment for the
cleaning and drying of the numerous cloth bags used to confine the ticks
on laboratory animals; dressing, locker and shower rooms for the use of
workers, who are expected to make a change of clothing on coming from
the field and on leaving the laboratory; a shop for the making of cages and
other equipment; a poison room for mixing and drying poisoned grain to be
used in the destruction of certain rodents; and quarters for the custodian.
A special feature of the equipment is a series of three refrigerator rooms
cooled by a Frick ammonia machine. These rooms are cork walled, two are
automatically maintained at 40 °C., and the third at 0°C. In these rooms
are fifteen thermal cabinets automatically maintained at graded tem-
peratures ranging from 0°C. to 37 °C. These cabinets are put to a variety
of uses including storage and incubation of cultures, virus, and vaccine, and
experimental work on ticks and parasites.

The building provides several rooms in which laboratory animals such
as guinea pigs and rabbits, and wild rodents such as ground squirrels, moun-
tain rats, and wild rabbits of various kinds, are held in cages stacked in steel
frames. The production of vaccine in quantity involves the feeding of a very
large number of infected ticks, as well as numerous tests on guinea pigs. Many
of the experiments on the virus and the studies of the organisms require the
use of laboratory animals. In the parasite work it is necessary not only to
parasitize the ticks while they are on animals but also to rear the ticks which
are to be parasitized. To prove that parasites have been established in the
experimental field areas and determine the percentage of parasitized ticks, wild
rodents must be trapped and held in cages until the ticks drop off.

It is thus necessary to hold a very large number of animals in cages in
the screened and guarded laboratories. This requires the daily feeding of
animals, often the taking of their temperatures, and at all times the keeping
of the cages and rooms in a clean and sanitary condition.

There are also provided two general laboratories equipped with facilities
for chemical and bacteriological studies. For the grinding of infected ticks
and further preparation of the vaccine, a special room with suitable facilities
is provided. There are also furnished office and record rooms and a photo-
graphic room. The rabbit hutches in the animal wing deserve special mention
as they are made in keeping with the established practice of rabbit breeders
in tlie Northwest. These hutclies are built in four tiers facing a hollow square

88 SEVENTH BIEXXIAL REPORT

01- court. While the four walls of the buildiug are complete, the roof is left
off in the portion over the court thus practically exposing the animals to the
open air, which exposure, growers have found, keeps rabbits in a healthier
condition. The guinea pig room, is of tighter construction and is given a
small amount of heat. A root cellar under this room provides ample space
for the storage of vegetables used in feeding the laboratory animals.