The turkey an important factor in the spread of gapeworms [Syngamus trachcalis]

UNITED STATES DEPARTMENT OF AGRICULTURE

Contribution from the Bureau of Animal Industry

JOHN R. MOHLER, Chief

Washington, D. C. A April 23, 1921

THE TURKEY AN IMPORTANT FACTOR IN THE
SPREAD OF GAPEWORMS.'

By B. H. Ransom, Chief, Zoological Division.

CONTENTS.

Page. Page.

Examination of market chickens Significance of turkeys in relation
ST Clee EY Sines 2 eres eS 1 to gapes formerly unrecognized__ 10

Experimental work £—~------_---__ 3 | Turkey the preferred host of the
Factors in the spread of gape FAVewoOrmie eee Eke Seng 10
SWAB 6) pe =e a ig =s 7 | How to avoid losses in chickens__-~ 11
Investigations on Maryland Conclusions 72= 228. 2 eee 12
Hiei) (2... a Sl) TWist jof- references 4. = 3)" =e ee 13

EXAMINATION OF MARKET CHICKENS AND TURKEYS.

OR THE PURPOSE of collecting some statistics on the preva-
lence of gapeworms (Syngamus trachealis) in the vicinity of
Washington, D. C., and of obtaining material for use in experiments,
examinations were made of the tracheas of 635 chickens killed for
sale at poultry stalls in Center Market during the latter half of
December, 1916, and the months of January and February, 1917.
Nothing definite is known as to the ages of these chickens except
that the chickens were all obviously large enough for food purposes.
Probably none were less than six months old, most of them likely
were older, and no doubt many were a year old or more. No gape-
worms were found.

At the same time the tracheas of turkeys from the same market
were similarly examined. The ages of the turkeys, as in the case of
the chickens, were uncertain, but undoubtedly all the turkeys were
at least 6 months old, and many of them were probably more than a
year old. During the period mentioned the tracheas from 386 tur-
keys were examined. The next year, beginning March 2, 1918, an-

1 The writer is greatly indebted to Dr. Lawrence Avery, of the Bureau of Animal In-
dustry, for assistance rendered in carrying out the investigations reported in this paper.
22888°—21—Bull. 939 1

2 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

other series of 115 was examined, and during the month of Novem-
ber, 1918, a final series of 178; in all, 679 turkey tracheas were ex-
amined. In the case of the chickens practically the entire trachea
was obtained from each bird, but in the case of the turkeys usually
only a portion of the trachea was secured, so that as a rule an exami-
nation of the entire trachea could not be made.

In the first series of turkey tracheas (386 examined in December,
1916, and January and February, 1917) gapeworms were found in
89, and characteristic lesions marking the former location of gape-
worms in 3 others, a total of 92, or 23.8 per cent. In the second series
(115 examined in March, 1918) worms were found in 17 and a gape-
worm lesion in 1 other, a total of 18, or 15.7 per cent. In the third
series (178 examined in November, 1918) worms were found in 48,
or 24.2 per cent. The percentage of turkey tracheas infested out of
the total number examined was 22.5 per cent. It is possible that the
lower percentage observed among the tracheas examined in March as
compared with those examined in December, January, and February,
and in November following, was the result of having more incomplete
specimens of tracheas than were generally secured in the two latter
series. In any event, in view of the fact that throughout the three
series incomplete tracheas were the rule, it appears quite certain that
more cases of infestation would have been found if the entire trachea
could always have been secured. It is, therefore, fair to conclude that
the percentage of infestation among the turkeys examined was in
reality higher than the 22.5 per cent actually found. Counting the
gapeworm lesions found without worms attached as representing
worms, and counting the paired male and female as a single worm, a
single worm was present in 91 cases, 2 worms in 36 cases, 3 worms in
14 cases, 4 worms in 6 cases, 5 worms in 3 cases, 7, 9, and 18 worms
in 1 case each.

In view of the complete absence of gapeworms from a large series
of adult and approximately adult chickens, and their common occur-
rence in a similar series of adult and approximately adult turkeys,
all obtained at the same market and at the same season of the year,
it would appear that adult chickens are poorly adapted as hosts
for gapeworms. Evidently the occurrence of gapeworms in adult
chickens in the general locality of Washington, D. C., must be ex-
ceedingly rare, though, as is well known, gapeworms are of frequent
occurrence in young chicks in this as well as in many other localities.
On the other hand, it is evident that not merely young turkeys may
harbor gapeworms, but that in the locality mentioned these parasites
are very common in adult turkeys. Although, as noted, the ages of
the various turkeys from the Washington market were uncertain,
many of the turkeys examined were no doubt considerably more than

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an i TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. 8
a year old. That turkeys above 3 years of age may harbor gape-
worms is established by the fact that a turkey which was kept at the
Bureau of Animal Industry Experiment Station, Bethesda, Md., for
three years after it was brought there was found after its death to
be infested with a pair of gapeworms.

EXPERIMENTAL WORK.

Experiments in artificially infecting chickens of various ages with
gapeworms were carried out as follows: To provide material for
infecting the chickens, cultures were made at first from gapeworms
collected from the tracheas of turkeys. Later many of the worms
collected from the artificially infected chickens were also used in mak-
ing cultures. The worms were chopped into small pieces and the
eggs released by tearing apart the fragments of the uteri in a small
quantity of water. The water containing particles of worms and the
eggs was spread on the surface of a sterilized medium culture made
from chicken feces mixed with powdered animal charcoal. This was
kept moist in a petri dish and allowed to incubate at room tempera-
ture. After about two weeks’ incubation a large proportion of the
eggs contained fully developed larvee, many of which commonly
hatched and continued active for long periods after hatching. The
cultures were then ready for use and were fed to the chickens by plac-
ing small portions scraped from the surface of the culture nredium
directly into the mouth and making sure that the birds swallowed the
material. The chickens used in the experiments, except the adults,
were hatched in incubators and kept from exposure to gapeworm
infection until used. Usually only one feeding was given, and in
most cases the chicken, if it did not die earlier, was killed two weeks
after feeding the infectious material. Occasionally chickens were
killed for examination in less than two weeks after infection. The
tracheas and lungs were examined for gapeworms, the latter by dis-
section in physiological salt solution, a lens being used for the dis-
covery of small, incompletely developed worms. Altogether 139
chickens of different ages were thus fed infectious gapeworm
material. The results are shown below.

Results of artificially infecting chickens with gapeworm material.

A J Number | Number | Per cent

‘Age of chickens when fed. fed. |infected. | infected.
DO 4awoeks Gee: S. 6 eens ste eases Be eee ee ec chee cee cs senbeeehetee gees 47 41 87
DitOSuWlOC KS a eee Beco cade cee Rea ie tee oe ae aoa aac soa Scio ice eimai 32 27 84
Oto 2Ohweeks cera tet cet hesaee be lots ood dot ccc ees Soe sso ie teeta ss. ee 32 21 66
DICWOEEKSIEO AG UMass ea ccaie se Bee coiate iis a einricmiscle sie cee tanis Sei eseee sp aoeees 28 8 29

4 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

From the data shown in the table it seems evident that as chickens
grow older they tend to become less susceptible to infection with gape-
worms. Apparently, therefore, the most likely reason no gapeworms
were found among the 635 chickens from the Washington market was
that these chickens when examined had reached an age at which they
were no longer favorable hosts for gapeworms. Probably some of
them had been infested earlier in life but had afterwards lost their
parasites. How long gapeworms will persist in youhg chickens that
do not succumb to the infestation is uncertain. That adult chickens,
however, in those unusual cases in which they become infested with
gapeworms, are likely to harbor the parasites only temporarily is
indicated by some of the findings in the following experiments :

Twelve adult chickens a year old or more were fed gapeworm
material from cultures on April 26, 28, 30, May 2, 4, 7, 9, and 11,
altogether receiving 8 feedings, except one which was killed May 7,
before feeding time, and hence received only 5 feedings. Material
from the same cultures was fed to 12 1-week-old chicks April 24,
98, 30, May 2, and 4. All the young chickens died of gapes in 11
to 27 days after the first feeding, and all were found infested with
gapeworms. Except the one killed May 7, 11 days after the first feed-
ing, the adult chickens were killed 16 to 29 days after the first
feeding and 1 to 14 days after the last feeding. Gapeworms
were found j in only 3 out of the 12. The lungs of one killed 16 days
after the first feeding and 1 day after the last feeding contained an
unpaired female 2.5 mm. long, and in the trachea were two pairs,
the females being 6.5 mm. and 10 mm. long, respectively. The 10
mm. female was producing eggs. Another chicken that was killed
18 days after the first feeding and 3 days after the last feeding har-
bored in the trachea a single pair of worms. The female of this pair
measured 13 mm. in length and was depositing eggs. In the trachea
of the third chicken, killed 29 days after the first odie and 14 days
after the last feeding, there were 7 dead males without females, 4
living males without females, 3 living females with dead males, 1
living female with a living male, and 1 living female without a male.
The last two females contained apparently viable eggs, but in the
other three females the eggs were apparently nonfertile, dark, and
unnatural in appearance. All the worms, alive and dead, were firmly
attached to the trachea. The living worms were enveloped in a thick
layer of mucus.

On another occasion 6 adult chickens probably a little less than a
year old were fed with a gapeworm culture. Seven days later one
was killed. No worms were found. A second chicken, killed 8 days
after feeding, had one unpaired worm, one pair of coupled worms in
the lungs, and 14 pairs of coupled worms in the trachea, all imma-

THE TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. 5

ture, those in the trachea evenly distributed from bronchi to larynx.
The females in the trachea measured 3 to 6 mm. in length. The
worms in the trachea were enveloped in masses of very viscid, tena-
cious mucus and none apparently were attached to the wall of the
trachea. Another chicken was killed 11 days after feeding and was
found to be free from parasites. Twenty-eight days after feeding,
microscopic examination failed to show gapeworm eggs in the feces
of the three surviving chickens. The following day one of them was
killed and found to be free from parasites. Thirty-one days after
the first feeding the two surviving chickens were fed with a gape-
worm culture. Eight days after this feeding the chickens were
killed. One of them was free from parasites, the other had one
young worm in the lungs, and a pair of coupled worms in the
trachea. The female of this pair was ruptured in removal but
measured 15 mm. or more in length and contained eggs ready for
oviposition. This pair of worms was enveloped in a mass of tena-
cious mucus. Evidently the werms in the trachea came from the first
feeding of gapeworm material, 39 days before the chicken was
killed.

The findings in the case of one of the chickens referred to sug-
gest very strongly that the worms that had succeeded in establishing
themselves in the trachea were having difficulty in maintaining them-
selves, as 10 of the 15 males present 29 days after infection were
dead though firmly attached to the trachea, and as the living worms,
both males and females, were enveloped in a thick layer of mucus,
indicative perhaps of a strong reaction, on the part of the host, that
would soon destroy them. In two of the other chickens also the
unusually large masses of mucus enveloping the worms suggest the
likelihood of the early death or expulsion of the parasites. In any
event it is evident, since in the one instance a large proportion
of the gapeworms present 29 days after infection had died after
reaching maturity, that gapeworms in adult chickens, when they
succeed in establishing themselves in the trachea, sometimes die
within a month after infection, infestation with gapeworms in
such cases thus being of brief duration. Further evidence of the
transient nature of gapeworm infestation in adult chickens is
given by Waite (1920, p. 115), who fed about 150 earthworms
from gapeworm-infested chicken runs to three yearling hens. Fif-
teen days later gapeworms could be distinctly seen in the tracheas
of two of them by looking down their throats in a good light. Two
weeks later the worms had disappeared, and when the hens were
killed and examined 72 days after the feeding with the earthworms,
no signs of gapeworms were found.

In view of the difficulty of infecting adult chickens with gape-
worms, the likelihood of the brief duration of infestation in cases in

6 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

which the worms succeed in developing to maturity in adult chickens
and the failure to find any gapeworms among a large number of
adult chickens obtained from a certain market, though the parasites
were of common occurrence in adult turkeys from the same market,
it seems evident that adult chickens are not likely to be of great im-
portance as carriers of gapeworms. On the other hand it is certain
that sometimes they may harbor gapeworms for brief periods at least.

Besides the fact that adult chickens occasionally may be infected ex-
perimentally may be cited the following instance of infestation follow-
ing exposure to infested ground. A chicken at least 22 months old and
probably considerably more than 2 years old died at the Bureau of
Animal Industry Experiment Station with a history indicating that
it had been kept at least a year in a pen that had previously been
used in gapeworm experiments. This hen was in poor condition,
greatly emaciated, and devoid of the usual subcutaneous and visceral
fat. Besides nematodes and tapeworms in the intestine there were
found in the trachea a female gapeworm 21 mm. long with a male
5 mm. long, and another female about 10 mm. long, with a male
4.6mm. long. The smaller female contained eggs, but well-developed
eggs were not found in the larger female.

This case perhaps should be taken as an indication of the possibility
that as chickens become old and debilitated their susceptibility to
gapeworms tends to increase again after having diminished as they
approached maturity. Such an explanation would be in harmony
with the frequently observed fact that certain parasites are more
common in young and very old animals than in those of middle age.
No definite conclusion, however, is possible from a single case.

In marked contrast to adult or nearly adult chickens, adult turkeys
can easily be infected experimentally with gapeworms, as would be
expected from the fact that the worms have been found to be
naturally common among adult turkeys. The following experiment
shows the results of attempts to infect chickens approaching ma-
turity, young chickens, and adult turkeys, respectively, using in-
fective material from the same source.

Three chickens 21 weeks old at the beginning of the experiment
were fed portions of gapeworm cultures November 29, December 18,
20, 27, January 3, 31, February 28, and March 31. Beginning Febru-
ary 28 the chickens were kept on ground that was contaminated with
gapeworms. The feces of these three chickens were examined Janu-
ary 3, 13, 17, 25, 31, February 8, 15, 22, 28, and March 28, and the
feces of two of them also on April 22, always with negative results.
One of the chickens was killed on April 8 and was free from gape-
worms, as were also the other two, killed on May 24.

Some of the culture fed on January 31 was fed on February 7 to
three chicks 8 weeks old, and these chicks when killed 14 days later

THE TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. "¢

harbored, respectively, 92, 75, and 36 pairs of gapeworms in their
tracheas, the females ranging in size from 4 to 11 mm. Besides the
worms in the trachea there were a few immature gapeworms in the
lungs of each chicken.

Some of the same culture was fed on February 7 to three turkeys
nearly a year old. Nineteen days later one of the turkeys was
observed to be sick and was killed. There were no gapeworms found
in the lungs, but 483 pairs were present in the trachea, the females
averaging 24 mm. in length. The feces of the two remaining turkeys
were first examined 21 days after infection and at this time con-
tained large numbers of gapeworm eggs. The birds were coughing
and there was a brown crust on their bills, formed by the drying of
expectorated mucus. On March 17, 38 days after infection, these
two turkeys were still coughing, but the brown crust was no longer
present on their bills. On April 14, 66 days after infection, gape-
worm eggs were still present in the feces. April 29, one of the
turkeys which had been ailing was killed, the lungs and one bronchus
being found affected with a gangrenous necrosis. The trachea
contained 22 pairs of gapeworms, the females averaging 33 mm. in
length; also many broken pieces of dead worms were found. The
third turkey was kept alive. December 16, 10 months after infection,
an examination of the feces of this turkey failed to show gapeworm
eggs.

In this experiment adult turkeys (nearly a year old) and young
chickens (8 weeks old) became heavily infested as the result of a
single feeding with gapeworm material, while chickens approaching
maturity (21 weeks old) that were fed repeatedly with gapeworm
material (including material from the same culture as that fed to
the turkeys and the young chickens) failed to become infested. Evi-
dently, therefore, adult turkeys and young chickens are much alike
in their susceptibility to gapeworm infection, and in this respect both
are quite different from adult chickens or chickens approaching
maturity.

FACTORS IN THE SPREAD OF GAPEWORMS.

From the results of the investigations briefly recorded above, it
would seem that turkeys are an important factor in the spread of the
gapeworm, and that adult chickens are relatively unimportant as
carriers of the parasite. Inthe perpetuation of gapeworms from year
to year on infested poultry farms the two chief factors appear to be
turkeys and contaminated soil. Whether guinea fowls are like turkeys
in commonly harboring gapeworms throughout life or whether they
are like chickens and tend to lose their susceptibility as they become
mature is uncertain. Little is known also as to the relation of pea-
fowls, ducks, geese, pigeons, and various wild birds to the spread of

8 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

gapeworms. There is little question, however, that the turkey is more
important than any other bird as a reservoir of infection, and it
is essential, if losses from gapes are to be avoided, that the part
played by the turkey in spreading and perpetuating gapeworms
should be borne in mind by the poultry raiser. The relation of the
turkey to gapes in chickens is commonly overlooked, largely, no
doubt, because young turkeys are usually less seriously affected
by gapeworms than young chickens, and because old turkeys har-
boring the parasites rarely show any visible evidence of infestation,
so that they are not likely to be suspected as a source of the disease
that plays havoc among the young chickens.

Whether, in the absence of turkeys from a farm, gapeworm dis-
ease among chickens will regularly disappear has not been definitely
established, but it seems probable that it may often do so. Though
it is certain that contaminated soil will remain infectious for a long
time and that infection in the soil may persist from one year to the
next, nevertheless it may be that, as a rule, chickens alone will not
perpetuate the infection. A large proportion of the young chickens
that become infested die of gapes before there has been much oppor-
tunity for scattering the eggs of the gapeworms, and since chickens
as they grow older tend to become not only less susceptible to infec-
tion but also more and more unfavorable as hosts of the gapeworms
acquired at an earlier age, the infested chickens that do not die of
gapes probably do not continue long to harbor the worms and so are
unlikely to spread much infection. In view of these apparent limita-
tions to the reinfection of the soil by chickens it seems not unlikely
that gapes will be found to have a tendency to disappear from places
where no turkeys are kept.

INVESTIGATIONS ON MARYLAND FARMS.

Evidence gathered from inquiries by Dr. Lawrence Avery and
the writer among poultry raisers in several localities in Mary-
land is insufficient to show that gapes will usually die out on farms
where there are no possible hosts other than chickens, but it is cor-
roborative of the statements that have been made as to the great im-
portance of the turkey as a source of infection. In fact, it was found
that in the absence of turkeys either no gapes occurred among the
chickens or the trouble from this cause was practically always slight.
On the other hand, where turkeys were present considerable losses
among the chickens as a result of gapes were almost always reported.
Inquiries were made on 41 farms. Gm 16 farms where there was
no history of the association of turkeys with the chickens, gapes
was reported in eight instances, no gapes in the other eight. On
one farm where there were said to be numerous cases of gapes
among a flock of 500 chickens, turkeys were kept the preceding

THE TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. 9

year, but it was said that they never came near the chicken yards.
A dozen guinea fowls were kept on this farm and mingled with
the chickens. On two other farms where there was said to be
considerable trouble with gapes, guinea fowls were kept in one case,
but there were neither guinea fowls nor turkeys in the other. On the
other 5 farms where gapes was reported in the absence of turkeys,
few cases were said to have occurred. On 25 farms where there was
evidence of the contamination of the chicken runs by turkeys, gapes
was reported in all but one case. Here there were about 300 chickens
and 70 turkeys roaming at will over the farm. The turkeys and
chickens, however, were housed on different plots of ground, neither
of which had been used for poultry during several years preceding.
On two farms there were said to have been no cases of gapes until
after turkeys were brought to the place. In another instance a man
who for five years had been on a farm where turkeys were kept by the
former occupant, had gapes among his chickens fora year or two after
coming to the farm, but had had none since. On two farms where
only a few cases of gapes occurred among the chickens, it was stated
that the turkeys were kept in the fields, and never or rarely were
brought into association with the chickens. On another farm where
there were a few cases of gapes no turkeys were kept, but turkeys
from the neighboring farm frequented the place. In a number of
other instances no turkeys were kept, but turkeys from neighboring
farms were accustomed to mingle with the chickens.

Two neighboring farms that were visited during the season of
the year when gapes is prevalent among young chickens afforded a
striking contrast. On one farm where turkeys were kept entirely
away from the chickens and never mingled with them nor came to
the place where the chickens were kept there had been no gapes
among the chickens. On the other farm several broods of young
chickens were confined in small pens on the lawn in front of the
farmhouse. Turkeys of various ages were feeding on the same
lawn. Many of the young chickens were showing the characteristic
symptoms of gapes.

Though the data that have been collected concerning gapes on
farms are necessarily more or less inaccurate because of the uncer-
tainty as to the reliability of the information given by the persons
of whom inquiries were made, the evidence obtained from this
source nevertheless indicates that in the localities in which the ques-
tion has been investigated gapes is more common and more serious
on farms where turkeys and chickens are kept together than on farms
where only chickens are kept, that the disease has a tendency to die
out in the absence of turkeys, and that it commonly does not appear
on a farm until after the introduction of turkeys.

10 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

SIGNIFICANCE OF TURKEYS IN RELATION TO GAPES FORMERLY
UNRECOGNIZED.

From the literature on gapes one may gather further evidence of
the importance of the turkey as a carrier of gapeworms, though the
peculiar significance of the turkey in relation to gapes has not been
recognized by former writers. In the first published record of gapes
Wiesenthal (1799) called attention to the frequent occurrence of the
disease in Maryland and stated that it was most prevalent among
young turkeys and chickens bred upon old-established farms. The
first published record of gapes in England is that of Montagu
(1811), who notes that it generally attacks chickens at the age of a
month to 6 weeks, and that it “seems to be peculiar to the young
of the common domestic fowl, since neither my turkeys nor ducks,
all of which are reared together upon the same spot, have even been
attacked.”

Von Poeci (1904), in discussing an outbreak of gapes among
young pheasants in Bavaria, which killed about 60 per cent of the
birds, incidentally remarks that turkeys were used as brood hens
for young pheasants. The first record of gapes in Norway (Horne,
1910) is based upon the discovery of gapeworms in two young
turkey poults and two young chickens from the same poultry farm.
How frequently turkeys have been associated with the occurrence
of gapeworms among chickens, pheasants, and other birds in Europe
is not indicated in the published reports that have come to the
writer’s attention other than those just mentioned. These, however,
are very suggestive and, together with the observations recorded in
the present paper, may be taken as an indication of the probability
that the turkey has been chiefly, if not entirely, responsible for the
spread of the gapeworm to various parts of the world.

TURKEY THE PREFERRED HOST OF THE GAPEWORM. ©

It would seem quite probable that the gapeworm, like the turkey,
was originally limited to America and that it has reached other
countries only as it has been carried by the turkey, which, because
of the tolerance it has to infestation with the gapeworm, may be
looked upon as the natural host of this parasite.

The fact that the gapeworm in turkeys grows to a larger size than
it does in chickens may be taken as evidence, in addition to that
already given, that the turkey as compared with the chicken is the
preferred host of the parasite. The difference in the size of the
worms may be a simple correlation with the size of the trachea, but
it seems more likely that other conditions than the mere size of the
trachea play a part in bringing about the differences in the size of
gapeworms in chickens and turkeys. The maximum length of gape-

THE TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. 11

worms observed by the writer in chickens 14 days after infection
has been 17 mm. Usually the length attained in this period is less,
commonly being 12 to 14 mm. The longest gapeworm observed by
the writer in chickens measured 21 mm. in length. This was found
in an old, debilitated chicken, mentioned on page 6, which had been
infested for an unknown period. Some of the gapeworms present in
an adult turkey 19 days after infection measured nearly 30 mm. in
length, and worms measuring 24 mm. were common. In natural cases
of infestation gapeworms in turkeys have been found commonly to
measure 30 to 40 mm. in length, and have been found as long as
50 mm. The measurements given are those of mature females that
had begun oviposition or that contained eggs ready to be deposited.

HOW TO AVOID LOSSES IN CHICKENS.

From what has been determined as to the frequent occurrence of
gapeworms in turkeys, the susceptibility of old as well as young
turkeys to gapeworm infection, the diminishing susceptibility of
chickens to infection as they grow older, and the rarity of gape-
worms among adult chickens, it would seem that the chief element in
the spread and maintenance of gapeworm infection, leaving infested
soil out of consideration, is the turkey. The eggs of the gapeworm
are scattered over the soil in the feces of infested turkeys. Later
some of these eggs or the larve that have hatched from them are
picked up again by the turkeys and more egg-producing worms de-
velop in them to add to the number of those already present. Thus
the stock of young worms in the soil and adult worms in the turkeys
is maintained. Meanwhile young chickens may also pick up gape-
worm eggs or larval worms from the ground where the eggs have
been distributed by the turkeys, with the result that they soon show
symptoms of gapes. As chickens young enough to be readily sus-
ceptible to infection with gapeworms usually die from gapes soon
after they begin to show symptoms of the disease they are not
likely to add much to the infection already in the soil. Older
chickens likewise do not scatter much infection because the eggs and
larval worms that they pick up either do not develop on account of
the diminished susceptibility of the chickens or, if the worms do
succeed in developing to egg-producing maturity, they are unlikely
to survive for more than brief periods. Chickens, therefore, may be
considered to play a small part, compared with turkeys, in infecting
the soil with gapeworms, and to be of minor importance as reservoirs
of infection. By keeping turkeys away from young chickens and
providing the latter with runs where there have been no turkeys
within a year or two and where, if used previously by young chickens,
there have been no cases of gapes in recent years, the danger of losses

12 BULLETIN 939, U. S. DEPARTMENT OF AGRICULTURE.

from gapeworm can be greatly reduced, inasmuch as infection of the
runs by the brood hens is not often likely to occur because of the
rarity of gapeworms among adult chickens. As the eggs and larve
of gapeworms have been kept alive in the laboratory for more than
eight months at a temperature ranging from 70° to 95° F., and for
more than a year at a temperature of about 50° F. (writer’s observa-
tions), it is advisable not to allow young chickens to run on once-
contaminated ground until after a considerable period of time has
elapsed, not less than a year at least, since its exposure to contamina-
tion. Consequently it is important in locating new runs for young
chickens on farms where gapes has been prevalent to select a spot that
is known to have been but little, if at all, frequented by turkeys within
at least a year. Naturally also it would be unwise to select a spot
where chickens with gapes had been the year before, even if in the
meantime there had been no chance of contamination by turkeys. As
a rule, in order easily to secure immunity from gapeworm losses
among chickens, it may be found necessary to abandon the keeping of
turkeys on farms where chickens are raised, because of the difficulty
of controlling the turkeys so as to prevent contamination of the
chicken runs. In fact the simplest way of preventing gapes among
chickens seems to be to exclude turkeys from farms where chickens
are raised.
CONCLUSIONS.

The turkey is probably the natural host of the gapeworm.

Adult turkeys as well as young turkeys commonly harbor gape-
worms though they may show no symptoms of infestation.

The turkey is apparently the chief agent in the spread of gape-
worms to new localities and is apparently the principal source of
infection to the soil on poultry farms where gapes is prevalent.

Gapes among chickens appears to be more prevalent on farms
where turkeys frequent the chicken runs than on farms where there
are no turkeys.

Available evidence indicates that gapes has a tendency to dis-
appear from farms following the removal of turkeys.

Chickens, unlike turkeys, are readily susceptible to infection with
gapeworms only while they are young. They become less susceptible
to infection as they grow older.

Adult chickens, at least in some localities, rarely harbor gape-
worms and hence in such localities are seldom likely to spread
infection.

In those instances in which gapeworms develop in adult chickens

or chickens approaching maturity the parasites are likely to live only
a short time.

THE TURKEY IMPORTANT IN THE SPREAD OF GAPEWORMS. 13

Ground contaminated by gapeworms is likely to remain infective
for at least a year after further infection of the soil has ceased.

Losses from gapes can be greatly reduced if not altogether avoided
by keeping young chickens on ground that has not been exposed to
contamination within at least a year and that is protected from further
contamination by excluding turkeys from it during its occupancy by
the chickens. As gapeworms appear rarely to occur in adult chickens,
brood hens may be associated with the young chickens with probably
little risk of infection to the latter from that source.

The simplest means of preventing or reducing losses from gapes
appears to be the exclusion of turkeys from farms where chickens
are raised.

LIST OF REFERENCES.

HORNE.
1910.—F ra veterinaerlaboratoriets daglige unders¢kelser. En kyllingsyg-
dom. (Syngamus trachealis) <Norsk Vet.-Tidsskr., Kristiania,
v. 22 (6), Juni, pp. 159-164, figs. 1-2.
MontTAGcu, GEORGE.
1811.—Account of a species of Fasciola which infests the trachea of poul-
try, with a mode of cure. [Read Aug. 1, 1808] <Ment. Werner
Nat. Hist. Soc., Edinb. (1S08--10), vy. 1, pp. 194-198, pl. 7, fig. 4.
von Pocci, FRANZ GRAF.
1904.—Der Fasan und sein gefiihrlichster Feind, der Rotwurm <Verhandl.
d. ornith. Gesellsch. in Bayern, Miinchen (1908), v. 4, n. F., v. 1,
pp. 102-118, figs. 1-8, 1 pl., figs. 1-5.
RANSOM, Brayton H.
1916.—Miscellaneous investigations of animal parasites <Rep. Chief Bu-
reau Animal Indust., U. 8S. Dept. Agric., Wash., p. 64.
1917.—Idem <Ann. Rep. Dept. Agric., Wash. (1916), p. 130.
1917.—Miscellaneous investigations of animal parasites <Rep. Chief
Bureau Anima! Indust., U. S. Dept. Agric., Wash., pp. 56-58.
1918.—Idem <Ann. Rep. Dept. Agric., Washington (1917), pp. 122-124.
1918.— Miscellaneous investigations of animal parasites <Rep. Chief Bu-
reau Aninral Indust., U. S. Dept. Agric., Wash., pp. 55-56.
1919.— Idem <Ann. Rep. Dept. Agric., Wash. (1918), pp. 125-126.
1920.—On the life-history of the gape-worm (Syngamus trachealis). (In
Proc. Am. Soc. Zool., 17. Ann. Meet., St. Louis, Mo., Dec. 29-31,
1919.) [Author’s abstract] < Anat. Rec., Phila., v. 17 (5), Jan.
20, pp. 330-331.
1920.—Gapeworm in turkeys and chickens. [Note read before 38. Meet.
Helminthol. Soc. Wash., Oct. 18, 1919] <J. Parasitol., Urbana,
Ill., v. 6 (4), June, pp. 200-201. [Issued Aug. 14.]
Waite, Roy H.
1920.—Earthworms—the important factor in the transmission of gapes in
chickens <Bull. 234, Maryland Agric. Exper. Station, College
Park, Jan., pp. 108-118, figs. 1-6.
WIESENTHAL, ANDREW.
1799.—[Gapes in poultry.] [Letter to editor, dated May 21, 1797] <Med.
& Phys. J., Lond., v. 2 (8), Oct., pp. 204-205, 2 figs.
4

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