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FOREIGN ANIMAL
DISEASES REPORT
FEBRUARY
1973
HOG CHOLERA ACTIVITIES
There were nine positive cases of hog cholera
diagnosed in five States during January,
including cases in Massachusetts (1), New
Jersey (1), North Carolina (2), Pennsylvania (1),
and Virginia (4) .
This brings the Fiscal Year total to 155 posi¬
tive and 252 exposed cases reported from
July 1 through January 31, 1973. During the
sane 7-month period 1 year ago, there were 40
positive and 147 exposed cases.
Quarantines ... As of January 31, 1973, the following areas were quarantined
because of hog cholera: the entire Commonwealth of Puerto Rico; the entire
State of New Jersey; portions of Charles, Prince Georges, and St. Marys Counties,
Maryland; portions of Bristol and Plymouth Counties, Massachusetts; portions
of Gates, Hertford, and Northampton Counties, North Carolina; a portion of
Berks County, Pennsylvania; and a portion of Southampton County, Virginia.
Increases in Hog Cholera Incidence in United States ... Statistics comparing
postives cases reported during 1971 and 1972, reflect the increase in hog
cholera incidence since December 1971. There were 100 positive cases diagnosed
in the U.S. from January 1, 1971 through June 30, 1971. During the last 6
months of 1971, only 18 cases were reported, nine of these occurring during
December, for a total of 118 cases for the year.
During 1972, 58 positive cases were reported during the first 6 months of the
year. One hundred forty six were reported from July 1 through December 31,
1972, with the bulk of them coming in August (25), September (54), October (32),
and November (19). Eight cases were reported in both July and December. The
1972 total of 204 cases represents a 73 percent increase from the 1971 total.
Recent positive cases close to the Dismal Swamp areas in Virginia and North
Carolina are quite disturbing. It is felt that unless all foci of infection
in this area are detected and eliminated prior to March 15, 1973, that this
will prove to be another trouble spot during the coming summer months.
Evidence of insect transmission of hog cholera occurred in the Dismal Swamp
area during the summer months of 1970.
MAR 2 8 1974
PROBABLE SOURCES OF INFECTION OF HOG CHOLERA (IN PERCENT)
Additions
Interstate Intrastate
Garbage
Vaccination
Area Spread
Undetermined
CY 1964
3.0%
18.2%
3.2%
8.5%
25.1%
42.0%
CY 1965
2.0
23.2
5.0
10.1
25.0
34.7
CY 1966
2.2
14.8
7.1
29.0
24.9
21.9
CY 1967
1.2
16.5
5.3
31.0
25.9
20.1
CY 1968
6.5
33.1
12.3
8.6
30.4
9.1
CY 1969
9.8
35.8
8.2
1.5
34.1
10.6
CY 1970
4.1
27.4
11.1
.3
44.3
12.8
CY 1971
1.7
33.8
14.4
2.5
22.9
24.6
CY 1972
6.8
24.5
18.1
«, —
34.3
16.1
Probable sources of positive cases which occurred from July 1 through
December 31, 1972, are interstate herd additions, eight percent; intrastate
herd additions, 16 percent; garbage, 21 percent; area spread, 41 percent; and
none established, 14 percent. These statistics indicate the need for greater
effort in the elimination of transmission of hog cholera through marketing
channels and uncooked or improperly cooked garbage fed to swine. The Carroll
County, Indiana outbreak which occurred during this period accounted for a
high percent of the cases attributed to area spread. This was due to large
numbers of swine in the area, very wet conditions, and a large insect
population.
HOG CHOLERA IN PENNSYLVANIA - IT COULD HAVE BEEN WORSE
On Friday, December 8th, hog cholera was diagnosed on a farm in Franconia
Township, Montgomery County. The disease was believed to originate from pigs
from hog cholera infected premises in New Jersey. These pigs had been sold
through two Pennsylvania livestock auctions. The Pennsylvania Bureau of
Animal Industry sent a team of veterinarians and inspectors headed by Dr. John
Dick into the area. After the farm was depopulated of swine and the area
quarantined, all premises to which swine had gone from those markets on the
days New Jersey swine were sold were traced back, inspected, and quarantined.
More than 100 farms were involved. Fortunately, the Federal Government had
placed an Exposure Quarantine on Pennsylvania which stopped movement of swine
out of the State. The Pennsylvania Department of Agriculture then issued a
Stop Movement Order which prevented movement of all swine within the State.
2
On December 12th, another outbreak occurred in a herd of about 100 swine in
Cumberland County. This outbreak was believed to have originated from butcher
shop offal from New Jersey swine slaughtered at Allentown. Possible exposure
herds in seven Pennsylvania counties were immediately placed under quarantine
surveillance.
By the Christmas weekend, both the Federal Exposure Quarantine and the State
Stop Movement Order for all classes of swine were lifted. On December 27th,
however, another outbreak in ten feeder pigs in Lehigh County was confirmed
by the laboratory. This one is apparently connected to the original imports
of infected pigs from New Jersey. At this date, December 30th, the Federal and
State area quarantines are still in effect. If further outbreaks occur, the
State may be forced to stop movement of at least feeder pigs and breeding
swine again.
Several things are apparent: The movement of swine is nothing short of
fantastic. As a result of pig movement through two Pennsylvania auctions,
more than one hundred farms were exposed to the possibility of hog cholera.
The Federal Exposure Quarantine and the State Stop Movement Order were
tremendously effective in preventing what might have been a disaster. The
Pennsylvania Bureau of Animal Industry and the USDA-APHIS handled the individ¬
ual outbreaks and their tracebacks in a very efficient manner. However, it might
well have been different if there had been continued swine traffic and a dozen
outbreaks resulting from traffic through additional markets.
The only sour note in the current problem is the knowledge that swine have
been vaccinated with BVD vaccine in New Jersey and one drug peddler is known to
have sold the BVD vaccine at a Pennsylvaina auction market. Several veterin¬
arians have reported that drug salesmen have been pressuring them to use BVD
vaccine for hog cholera protection. Widespread use of this vaccine could
wreck the nationwide effort to eradicate the disease. Regardless of what the
drug salesmen say, MLV-BVD vaccine is not approved for such use, and there are
many valid reasons why it should not be used - legally or otherwise.
One last note: There must be a larger than usual amount of virus contaminated
or infected pork around as a result of slaughter of large numbers of New Jersey
swine in eastern Pennsylvaina slaughterhouses. This will serve as a potent
source of virus for some time to come. Warn swine producers to feed no garbage
not even table scraps, unless it is thoroughly cooked. (From Veterinary News
Letter No. 66, December 1972, University Park, Pennsylvania, 16802).
FOOT-AND-MOUTH DISEASE UNDER CONTROL IN BULGARIA
Ministry of Agriculture in Sofia, informed American officials on December 19,
1972, that no foot-and-mouth disease (FMD) exists in that country and necessary
precautions were taken to prevent its spread from the neighboring countries.
The Ministry has delayed sending Bulgarian veterinarians to the U.S. for
training because they are extremely busy conducting control programs at borders.
In an informal conversation with local veterinarians, American Embassy officials
were told that a small outbreak of FMD in pigs had occurred in the second week
of November, but had been brought under control.
3
EXOTIC NEWCASTLE DISEASE ACTIVITIES REPORT
During the month of January 1973, exotic Newcastle disease was diagnosed in 16
flocks comprised of slightly more than 230,000 birds. One hundred and twenty
flocks consisting of slightly more than 144,000 birds were determined to be
exposed. The exposed flocks as well as the infected flocks were in the Norco,
Banning, Corona, Woodcrest, Perris, Redlands, Chino, Cherry Valley, and River¬
side areas of Riverside County, and Yucaipa, Ontario and Highland areas of
San Bernardino County.
As of February 1, 1973, 973 flocks comprised of slightly more than 10 million
birds in southern California had been determined to be infected or exposed
since the declaration of the national emergency by Secretary of Agriculture
Butz on March 14, 1972. These birds were appraised at slightly under $20
mill ion.
In January of 1973, the area around Cherry V alley, Beaumont, Calimesa, Yucaipa,
Redlands, Highland, and Mentone which was designated as a high-risk area by the
task force, was removed from this designation. Permits are now being issued
for the shipment of poultry into this area as it was {previous to the declaration
of the high-risk area. This action was taken after it was determined through
the evaluation of flocks with sentinel birds, Epidemiological Necropsy Surveil¬
lance Program (ENSP), and investigations and inspections, that the area was no
longer a high-risk area. In the area currently under quarantine for exotic
Newcastle disease, 3,356,000 birds were vaccinated in commercial flocks as a
part of the fourth round of vaccination.
As of February 1, 1973, almost 109 million birds immunizations had been completed
since the program began on March 14, 1972. Slightly over 12 million bird
immunizations have occurred during the fourth round of vaccination. These
consisted of 328 commercial chicken flocks comprised of slightly over 12 million
birds and 4 turkey flocks consisting of slightly more than 92,000 birds.
On January 23, 1973, exotic Newcastle disease was confirmed in a flock of 27
game birds in Los Ebanos, Hidalgo County, Texas. This area is a s parcel y
populated poultry area and the flocks are primarily of game birds and other
backyard type chickens. Portions of southeastern Hidalgo and southwestern
Starr Counties have been placed under State and Federal quarantines. Intensive
surveillance of the area is in progress. In addition to the one infected flock,
52 additional flocks comprised of 422 birds were determined to be exposed. All
of the exposed and the one infected flock have been depopulated and the premises
have been cleaned and disinfected. Intensive surveillance of the area to date
indicates that there was no spread of infection. One thousand sentinel birds
have been acquired to place in flocks within the quarantine area and on the
premises which have been depopulated. These birds will also be used to evaluate
flocks outside of the quarantine area.
Surveillance Activities ... As indicated above, intensive surveillance activities
are underway in Texas as well as in southern California. Sentinel birds continue
to play a very important role in the exotic Newcastle disease surveillance
program. Over 11,570 sentinel birds have been placed in 2,222 backyard flocks
and over 23,000 sentinel birds have been placed in 440 commercial flocks. One
flock was diagnosed positive by this means in January giving a total of 22
4
commercial flocks and one backyard flock which have been diagnosed positive by
the use of sentinel birds. During the month of January, ENSP was responsible
for the confirmation of the disease in one flock in southern California. Thus
far, 12 flocks have been diagnosed positive as a result of ENSP. Eighty-five
percent of the commercial flocks in San Bernardino and Riverside Counties
which are under quarantine are under ENSP. Approximately 80 percent of the
commercial flocks in Orange, Los Angeles, Riverside, San Bernardino, and
San Diego Counties, California, are under the ENSP.
On January 9, 1973, the State-Federal Exotic Newcastle Disease Eradication Task
Force, headquartered at Riverside, California, consolidated its field office at
Ontario with the Riverside office. The field office at Thousand Oaks in Ventura
County will remain open to service that area. It will be closed about the
first of March leaving the headquarters at Riverside as the only office.
On January 31, 1973, a press release was issued from Riverside, California
which stated that the drive to eradicate exotic Newcastle disease from southern
California is entering one Of its toughest phases which is finding the remain¬
ing infection. The eradication effort in the coming weeks will be concentrating
its forces on areas where the disease appears to be localized. Eradication
depends upon finding and destryoing the last bird infected with or exposed to
exotic Newcastle disease. All bird owners were asked tq promptly report any
signs of the virus disease to the Riverside task force office. An important
element during this period of the eradication effort is a three-prong surveil¬
lance program now in operation throughout southern California. The purpose
of this surveillance program is to rapidly identify exotic Newcastle disease
through the use of three basic diagnostic tools. These are examination of bird
deaths in each flock or ENSP, the use of sentinel birds, and on-sight inspections
through investigations and surveys.
Regulation Changes and Quarantine Actions ... On January 23, 1973, exotic
Newcastle disease was confirmed in a flock of predominately game birds in Los
Ebanos, Hidalgo County, Texas. As a result, a portion of southwestern Hidalgo
and southeastern Starr Counties, Texas, was placed under a State and Federal
quarantine. A radius in excess of 5 miles of the infected premises was
quarantined.
On January 31, 1973, a docket was prepared which will release portions of San
Bernardino and Riverside County, California. A small portion of Riverside
County near Riverside, California, will be requarantined as a result of this
action. The area under quarantine in southern California will be reduced from
1,450 square miles to 690 square miles. County areas remaining under quarantine
will be comprised of 260 square miles in Riverside, 270 square miles in San
Bernardino, and 160 square miles in Ventura.
On January 8, 1973, the U.S. Department of Agriculture banned the importation
of all fresh poultry meat into the United States and placed restrictions on the
importation of table eggs. The action was taken by USDA's Animal and Plant
Health Inspection Service (APHIS) because of recent shipments and planned ship¬
ments from countries infected with exotic Newcastle disease. It is designed to
further protect the Nation's supply of poultry and eggs against the introduction
of exotic Newcastle disease which affects poultry and other birds.
5
APHIS officials said the prohibition on imports covers all fresh, chilled, and
frozen poultry carcasses and parts. The only exception is Canadian poultry
meat shipped directly to the United States, since Canadian officials are also
following an eradication program against the disease.
The restrictions on table eggs requires that all imported eggs be washed,
sanitized, and packed in new cartons, flats, dividers, and crates. These eggs
must also be certified by a veterinary official of the exporting Nation as hav¬
ing come from flocks proven to be free of exotic Newcastle disease through the
use of sentinel birds.
Certification will not be required if the eggs are sent under seal directly
from the port of entry to an approved egg processing plant for breaking and
pasteurization under Federal egg inspection supervision. The same exemption
for poultry meat from Canada will cover eggs imported from Canada.
APHIS officials explained that while this disease does not affect persons who
eat poultry meat and egg products, the action was taken as a precautionary
measure to prevent the exotic Newcastle disease virus from again being spread
to U.S. poultry flocks, where losses could greatly reduce the supply of poultry
and eggs available to American consumers.
The new regulations became effective immediately, and cover all poultry and egg
shipments to the U.S. Special conditions are provided for table eggs consigned
to U.S. buyers on or before the effective date of the regulation.
Special exceptions for individual importations can be made by APHIS officials
for educational, scientific, and research institutions with the facilities and
equipment to safely receive and handle potential disease bearing materials.
Migratory bird carcasses being imported by hunters are exempt from the regula¬
tions.
On January 24, 1973, the U.S. Department of Agriculture (USDA) proposed regula¬
tions which, if adopted, will permit the importation of pet and exotic birds.
The imports would be in commercial lots and under strict controls. USDA noted
that the original introduction of the disease in southern California is believed
to have resulted from the importation of infected exotic pet birds.
A ban on the importation of such birds was imposed on August 24, 1972, to help
prevent further introduction of exotic Newcastle disease into this country.
This ban is still in effect.
The proposed regulation would require inspection, testing, and quarantine of
imported birds under direction of USDA's Animal and Plant Health Inspection
Service (APHIS). It calls for the overseas inspection of each shipment by a
full-time salaried veterinarian, employed by the exporting Nation, who would
have to certify that the birds are free of communicable poultry diseases, in¬
cluding exotic Newcastle disease.
The certification would also have to state that the location of the origin of
the birds was free of evidence of disease, had not been under quarantine for
at least 90 days prior to shipment, and that the birds had not been vaccinated
for Newcastle disease.
6
The proposed regulations would require commercial bird importers to provide
quarantine facilities in this country at specified ports of entry where the
birds would be held in isolation for a 30-day period. The facilities would
have to be approved by APHIS and located in the immediate vicinity of the port
through which the birds entered the U.S. Except for birds from Canada and
Mexico, commercial shipments would have to enter at New York City, N.Y.;
Miami, Fla.; San Ysidro or Los Angeles, California; Seattle, Washington; or
Honolulu, Hawaii. Commercial shipments from Canada would have to enter at
Seattle, Washington; Detroit, Michigan; or New York, N.Y. Those from Mexico
would have to enter at Miami, Fla.; Los Angeles, or San Ysidro, California; or
Brownsville or El Paso, Texas.
Birds entering the quarantine facilities would be handled on an "all in - all
out" basis so that all of the birds could be treated as a single lot during the
quarantine period. Each bird in the lot must be individually identified by
methods approved by APHIS.
Importors would have to meet APHIS operating standards for quarantine facilities,
including inspection and testing under the supervision of an APHIS veterinarian
at the port of entry.
The importer, under the proposed regulations, would bear the costs of main¬
taining the quarantine facility in an APHIS-approved status and the costs of
feeding and caring for the birds while they are in quarantine. APHIS would
provide the services of qualified veterinary personnel for the required inspec¬
tions and tests.
The proposed regulations appeared in the Federal Register on January 25, 1973.
A period of 30 days will be allowed for public comment. Any comments should be
sent to the Deputy Administrator, Veterinary Services, APHIS, USDA, Hyattsville,
Maryland, 20782.
Other Activities ... Dr. R. E. Omohundro, Director, Emergency Programs,
participated on the program of the annual Southeastern International Poultry
Convention of Southeastern Poultry and Egg Association, January 28-31, 1973,
Atlanta, Georgia, to discuss the subject "immunization versus vaccination."
Representatives of the poultry industry throughout the United States were in
attendance. A speaker from Venezuela was also on the program and discussed
exotic Newcastle disease in his country. During this meeting, the Animal and
Plant Health Inspection Service (APHIS) Information Division presented a dis¬
play depicting the activities of the exotic Newcastle disease program. A film
on the program in southern California was also shown to persons in attendance.
This film is being duplicated for distribution to field stations and other
people interested in its use.
A full-time information officer has been employed and assigned to the Newcastle
disease task force in Riverside, California. The information officer will be
extremely helpful in disseminating current information about the progress and
direction of the exotic Newcastle disease program.
Four courses pertaining to commercial, pet, and wild bird medicine were sched¬
uled for four locations throughout the United States to train Veterinary
Services personnel in inspection procedures and other information which will
7
be needed in dealing with exotic Newcastle disease and the standards and
regulations which are proposed to allow the importation of pet and exotic
birds. One of these courses was held in Atlanta, Georgia, during the period
of January 29 through February 2, 1973. Other courses are scheduled at
Stony Brook, New York, February 12-16, 1973; Chicago, Illinois, February 26
through March 3, 1973, and Los Angeles, California, March 5-9, 1973. These
programs have been planned and organized by the Poultry Diseases Staff of
Veterinary Services. These courses consist of 32 instructional hours and have
the following basic objectives: (1) Familiarize participants with diseases
of commercial, pet, and wild birds and with techniques of handling and diagnosis,
(2) Review regulations controlling importation and movement of birds and outline
responsibilities of three different agencies, (3) Enable participants to
communicate with bird fanciers, with persons in the commercial industry and with
avian pathologists, (4) Outline the epidemiology of diseases in wild, pet, and
commercial birds as related to health problems in commercial poultry, and
(5) Establish contacts and sources of information that will provide the basis
of a continuing relationship with avian pathologists and the commercial bird
industry.
SWINE VESICULAR DISEASE
In a special bulletin dated December 19, 1972, we reported on a disease of
swine occurring in Great Britain caused by a porcine enterovirus and called
"Swine Vesicular Disease" (SVD).
Since then we have learned that there have also been outbreaks of SVD in Austria,
France, Italy, and Poland. From information available at present, it would
appear that the disease is currently limited in its distribution to Europe.
Our latest information reveals that SVD is being effectively controlled in
Great Britain with about 90 percent of the outbreaks traced to a source. There
have been approximately 41 outbreaks involving 15-20,000 swine in Great Britain
since the initial outbreak on December 11, 1972.
It is recognized that SVD is of great importance as a disease of swine. It also
represents a very complicating factor in the control of Foot-and-Mouth disease
(FMD). It would be extremely difficult to exert effective control of FMD if
swine vesicular disease became widespread. In the case of an outbreak of
vesicular disease affecting swine and not cattle, it is important to establish
as quickly as possible the differential diagnosis from FMD, and especially to
determine that FMD is not present either alone or in mixed infection with
swine vesicular disease.
Various laboratory methods may be used to differentiate SVD from other vesicular
diseases. On January 9, 1973, an emergency meeting of the Food and Agriculture
Organization's European Commission for the Control of Foot-and-Mouth Disease
was held in Rome, Italy. The participants discussed the present SVD and FMD
situation in Eastern and Southeastern Europe and came up with a list of the
most important methods to be used in differentiating SVD and FMD:
8
1. The growth of the virus in a number of different tissue culture
systems. The porcine enterovirus grows in certain tissue cultures
of porcine origin (IB-RS-2 cell line, primary pig kidney culture,
etc.) but not in those of bovine origin (calf thyroid, bovine
kidney, etc.).
2. The demonstration of resistance of the virus to pH 5.0 and its
stabilization by IM MgCl 2 against heating at 50°C.
3. The demonstration of specific complement-fixation and/or serum
neutralization between the new isolate and known antisera.
4. Additional criteria are:
(a) Failure to infect cattle by experimental inoculation.
(b) Demonstration of particles of about 30 nm in the
electron microscope (compared with about 25 nm for FMD).
(c) Determination of buoyant density of virus particles
at 1.32-1.34 as compared with 1.43-1.44 for FMD.
(d) Demonstration of infection of day-old mice (differentiating
from the virus of vesicular exanthema but not from FMD).
It is well to note that the five primary breaks of SVD in Great Britain were
caused by feeding infected garbage to swine. Direct contact and market move¬
ments took it from there.
In addition, the Commission has recommended that control measures be taken
immediately, exactly as if the outbreaks were proven cases of FMD. The measures
include, when possible, slaughter of infected and in-contact pigs and destruc¬
tion of carcasses.
EXOTIC NEWCASTLE DISEASE IN CANADA
On November 13, 1972, a shipment of 400-day old chicks was received in Calgary,
Alberta, from a Puyallup Washington Hatchery. On the same day 2600 day-old
chicks were received from a hatchery in Canada. None of the chicks were
vaccinated. On or about the 10th day chicks began dying and by the 3rd week
all 3000 chicks were dead. Velogenic Newcastle disease was diagnosed by
Canadian officials. Adult birds in the flock were destroyed. A quarantine
was placed on an area including all surrounding premises.
FIELD STUDIES ON BROILER VACCINATION
AGAINST EXOTIC NEWCASTLE DISEASE
Dr. C. W. Beard, Director of the USDA, Agricultural Research Service, Southeast
Poultry Research Laboratory, Athens, Georgia, and Dr. Dyarl D. King, USDA,
Veterinary Services, have initiated field studies on Newcastle vaccination
9
programs in broilers. As of January 26, 1973, the following is a summary of
their findings in one very large broiler operation which is presently under
study.
1. The breeders are well immunized, have good HI titers and most will
survive viscerotropic velogenic Newcastle disease (VVND) challenge.
2. The chicks have variable levels of parental antibodies when placed in
the house (parental antibodies will not protect against VVND).
3. Drinking water administration of either B-j or La Sota strains of
Newcastle vaccine at 10 or 17 days (depending on breeder flock source) was the
broiler vaccination program.
4. The drinking water program provides 70 to 90 percent protection
against the lethal effects of VVND 3 and 5 weeks after vaccination. Additional
birds become crippled and paralyzed, which in field rearing conditions would
be synonymous with mortality. Almost all of the birds are infected, sick, and
shed virulent virus. They show severe respiratory symptoms with depression
during the illness.
5. Vaccine virus survives very well in the water troughs in poultry
houses. Generally, the higher the vaccine titer, the better the immune response.
6. The HI test continues to be a reliable indicator of what to expect
when the birds are challenged. Broilers with negative HI titers usually die,
with the incidence of mortality decreasing as the HI titers increase.
7. Limited spray trials in Ibroiler houses have resulted in less adverse
reaction than initially anticipated, and the HI titer response has also been
less than anticipated. The reasons for this are being explored as the trials
continue.
In summary, the experimental results to date indicate that exotic Newcastle
disease and a broiler loperation are incompatible. The broilers from well
immunized breeder flocks are susceptible to the lethal affects of VVND and
therefore, it will be difficult or impossible to protect broilers for their
entire 8-week life by vaccination. Vaccination will certainly reduce the im¬
pact of VVND on the broiler but it will no longer be the efficient low-cost
source of meat protein.
It is hoped that these vaccine research efforts can be continued in the field
with the goal of developing a program that will provide the most protection at
the earliest time and for the longest period with the least adverse reaction.
This is a monumental challenge but is a very necessary one that must be success¬
fully met.
10
EPIDEMIOLOGY AND EMERGENCY DISEASES
Purpose ... Epidemiology, like disease, is not new. The term "epidemiology"
appeared around the year 1800. Epidemiological techniques, however, have been
used for thousands of years to explore the natural history of diseases in human
and animal populations. Refinements have accrued, the latest, within the last
50 years, being statistical measurement of data. But whether an investigation
concerned the influence of noxious vapors on health in ancient Greece, the
causes of poisoning among cider drinkers in medieval England, or the status of
vesicular stomatitis in a rainforest in present-day Panama, the purpose of the
inquiry was fundamentally the same - to understand how the disease appeared and
spread, and to develop methods of control.
The epidemiologist ... Usually disease arises and is maintained by an interac¬
tion of multiple causes. These may be related to the animal host, specific
agents, or the environment. They may be associated with the climate or geog¬
raphy; micro-organism, toxins, or nutrition; arthropods or wildlife; housing,
husbandry, or management. The epidemiologist observes, describes, and analyses
these aspects of the disease problem. He does not purposely seek new knowledge
about the nature of disease, though it may follow from routine investigations.
Rather, the epidemiologist is concerned with the practical application of what
is already known about etiology to explain and to cope with the disease problem.
While investigations are individually motivated and directed, the epidemiologist,
as a generalist, neither works alone nor personally follows all avenues of
inquiry. The implications of modern disease frequently are so broad that
assistance may be sought from specialists in microbiology, pathology, parasitol¬
ogy, toxicology, virology, or biostatistics. The epidemiologist fits these
contributions into a mosaic to create a pattern of causal associations and
explanations.
Frequently, associations between events are spoken of as cause and effect, the
first event being denoted the "cause" of the second. The concept that effect
is tied to cause and is an infallible consequence of it, however, has been
rejected by schools of philosophy for several hundred years. One event follows
another. But regardless of the duration of association, there is nothing
inevitable about causal associations, nor are effects ever dependent on single
causes.
The epidemiologist is concerned with the discovery of relationships. For this
purpose, a causal association may be defined as a relationship between two
categories of events in which a change in the frequency or quality of one
follows alteration in the other. When related events occur simultaneously,
they cannot be considered causal. The stronger the association and the higher
the ratio of incidence of B following A to the incidence of B without A, the
greater the possibility of a causal relationship.
Variables in epidemiological investigations ... An epidemiological inquiry
starts with questions which are influenced by the information already available.
The variables not commonly examined and measured relate to the agent, the host,
and the environment.
11
The agent ... The agent is usually thought of as something tangible -- a
virus, a bacterium, a mycoplasma, or a chemical or physical agent. The agent
may also be a chemical poisoning, trauma, or a carcinogen. To the epidemiol¬
ogist, however, the concept of the etiologic agent as the single cause of
disease is an oversimplification. One event follows another, but regardless of
the duration of their association there is nothing inevitable about causal
associations, nor are effects ever dependent upon single causes.
The host ... Numerous elements influence host response to disease. Some of
these are age, sex, and breed. Others are physical structure and metabolism.
Genetic inheritance may determine resistance or susceptibility to certain
diseases. This hereditary pattern may be limited to the individual, to a breed
or to a strain. Variations in host response to disease may also be influenced
by previous artifical immunizations, nutrition, hormones, vitamins, and steroid
therapy. Resistance usually increases with age. Resistance in a population
resulting from prior exposure to disease is called herd immunity.
The environment ... The influence of environment on disease was recognized long
before epidemiology became a science. Hippocrates, 2300 years ago, advised
for proper medical investigations, to consider the seasons and their effects,
the winds, the waters, and the condition and elevation of the ground.
The epidemiologist seeks to identify and to control the elements that cause
disease. In his search for causal associations and relationships, the
epidemiologist must explore the entire environment. This has two phases: the
macro-environment which includes topography, altitude, time, temperature,
season, moisture, rainfall, winds, soil, water, and vegetation; and the micro¬
environment which includes interrelationships with other animals of the same
and different species, arthropods, rodents, birds, feed, sanitation, population
density, ventilation, and all the aspects of management in a barn or a house.
Epidemiologists basically are fact finders. In the search for determinants of
disease, therefore, epidemiological investigations are only as good as the data
collected. Incomplete or inaccurate information can lead to erroneous conclu¬
sions or deleterious decisions. The principal methods for collecting data are
observation and questionnaire-interview.
Observations ... Whether it is done in the laboratory or in the field,
observation is fundamental to all scientific inquiry. The objective is to
obtain facts that may serve as the basis for generalizations beyond observation
While observations usually are systematic and related to the disease situation,
even chance impressions may be significant. Since memory is fall iabl e ,
epidemiologists are rigorous note- takers. Particularly in field investigations,
data will be more reliably retrieved if it is immediately recorded. At the end
of the day notes are elaborated into a narrative as a' basis for subsequent
reports.
The best repository for information is a diary. If immediate recording in the
diary is not feasible, jotting down key words on a small sheet of paper may
suffice until more detailed notes are possible.
12
As survey situations differ in origin and development, so do observations as
investigations progress. Thus, initial impressions and judgments, as well as
continuous interpretation of data and events, are important. Clear separation
of observation from interpretation, however, helps headquarters to understand
and to evaluate the complete animal health picture.
Questionnaire- interview ... This technique for data collection complements
field observations. The questionnaire for "epidemiological study of animal
health" provides a format for an investigation, while not limiting improvisation
and change as the progress of investigation opens new avenues of exploration.
In chronological sequence, the epidemiologist has his first interview and
obtains preliminary data usually from the veterinarian who precedes him to
the premises and with whom thereafter he works closely. Subsequently, the
more channels of communication the epidemiologist establishes, the greater the
possibility of obtaining useful information. Discrepancies in the accounts of
informants are investigated further.
The written questions are both closed and standardized (i.e., require factual
information), as well as open-end (i.e., to permit extended explanation). The
interview is similarly loosely structured to permit the epidemiologist to
acquire as much information and opinion as he believes material.
Good epidemiology is one thought stimulating another. And every epidemiological
investigation is a unique experience iwithin itself.
Answers are recorded when given. Lengthy answers may be carried to the back
of the sheet or to the diary. If the individual is reluctant or unable to give
certain information, answers often may be tactfully obtained from other members
of the household or from hired help. Regardless of their place in the question¬
naire, questions concerning livestock numbers are best posed at the end of the
interview.
An indexing system in the diary consistent with coding in the questionnaire,
names of persons, and dates is helpful for reports and reference.
Supplementary to diaries and reports, a plan of the premises, spot maps
showing geographic distribution of the disease, and graphs portraying disease
incidence by weeks help establish time and space relationships of the disease
under investigations.
Submission of data ... Significant information is reported by telephone to the
chief epidemiologist at the reporting center. Questionnaires, premises plans,
and spot maps are submitted to the appropriate State or national center as
soon as they are completed. Field reports, including supplementary observa¬
tions, hypotheses, and interpretations, are submitted each week, Identified
by case number, data are assembled, categorized, coded, and recorded on marginal
punch cards for analysis and evaluation.
Epidemiology in animal health reporting ... Establishment of an agent-host
relationship is important in the control of diseases. But this is only one
aspect of epidemiology. More emphasis is needed on the "why?" — not only of
13
specific disease outbreaks, but of total animal health. Epidemiologists
assisted by laboratory intelligence are the best agents for obtaining a
complete evaluation of animal health in relation to the total environment.
Modern epidemiology is largely analytical (or statistical) and experimental.
The analytical method relies upon legwork to gather field data. When acute
diseases are involved, investigations must be made rapidly. When chronic
diseases are concerned, the epidemiological approach is retrospective and less
urgent. In the former (and complicating the need for speed), thorough know¬
ledge of the disease and the organisms involved is initally essential in plan¬
ning the course and content of the investigation. In the case of chronic
diseases on the other hand, since retrospective investigations are after-the-
fact, trails usually a'-e less clear, gathering information is more difficult,
and definitive conclusions are less certain.
Although built on enumeration, epidemiology in emergency programs is not like
counting cabbages. Statistics can put information in an orderly arrangement
for machine processing; but epidemiology usually starts where computers stop.
The disease process, though convoluted, is a continuum. The web of causation
cannot be unravelled without an understanding of all the interrelationships
of agent, host, and environment; nor can the associations of disease, treat¬
ment, and outcome be determined without epidemiological studies. Only this
complete approach will help reveal the true dimensions of total animal health.
TABANID CONTROL DURING HOG CHOLERA ERADICATION
Although research conducted in North Carolina has incriminated tabanids
(horse flies and deer flies) as potential mechanical vectors of hog cholera
virus (Tidwell et al_. , 1972, Am. J. Vet. Res. 33:615-622), this group of insects
is among the most difficult to control. Therefore, a seminar on Tabanid Control
During Hog Cholera Eradication was held on February 8, 1973, at the Emergency
Programs Information Center to bring together experts with the latest infor¬
mation on the subject. Invited participants included scientists from Auburn
University, Clemson University, Rutgers University, the Agricultural Research
Service, and the Animal and Plant Health Inspection Service.
Reviewed during the deliberations were the current state of knowledge regarding
tabanid biology and control, the possibilities for initiating an operational
control program, and areas of study requiring additional research and develop¬
ment. General indications are that, at the present time, no techniques are
available which will provide tabanid control for periods of more than 24 to
48 hours. As a result, programs are being planned to provide operational
information which can be applied to the hog cholera eradication program as
soon as possible.
14
VESICULAR DISEASES IN THE WESTERN HEMISPHERE*
FMD VS
Country
Period 1972
0
A
C
New Jersey
Indii
Argentina
Sept. 1-Nov. 15
277
261
15
Bolivia
Sept. 1-15
-
7
-
-
-
Brazil
Aug. 12-Dec. 5
42
69
92
-
-
Costa Rica
Dec. 1-15
-
-
-
1
-
Ecuador
Aug. 1-Dec. 31
89
4
-
-
-
Guatemala
Nov. 16-Dec. 15
-
-
-
2
-
Honduras
Nov. 16- Dec. 31
-
-
-
2
-
Mexico
Nov. 1-Dec. 15
-
-
-
2
-
Paraguay
Dec. 1-15
-
-
1
-
-
Peru
Nov. 16- Dec. 31
6
3
-
-
-
Venezuela
Sept. 1-Dec. 31
8
1
-
4
-
Epidemiological Notes:
Bol ivia ... Foot-and-Mouth Disease appeared during 1971 in seven out of the
nine districts of the country, at different times, with the exception of the
district of Cochabamba, in which it appeared simultaneously with other districts.
The majority of the outbreaks did not proliferate, and were controlled with
pertinent health measures and with the inclusion in the vaccine or subtype 0]
virus. This subtype caused the outbreaks.
In 1972, foot-and-mouth disease affected another district, Tarija, where the
disease was absent since 1946. Subtype Oi virus was identified. In August,
a new outbreak appeared in the district of Cochabamba. The virus which caused
this outbreak was identified as type A, and the subtype is still under study.
Mexico ... Vesicular Stomatitis affected 240 bovines.
Peru ... Foot-and-mouth disease affected 56 bovines and 45 swine. The subtype
0] virus was identified on November 2, on two premises. Out of a total number
of 2113 cattle - from five farms - 56 were registered as affected and slaughtered
in the neighboring slaughterhouse.
Argentina ... Due to a foot-and-mouth disease focus detected in the locality
Colonia Sarmiento (Province of Chubut), declared free of the disease since
June 11, 1969, according to the requirements of the 6th article of the
International Zoosanitary Code of the International Office of Epizootics, on
the 22nd of this month, all the susceptible animals in the above mentioned zone,
healthy and ill, were slaughtered, according to the 6th article of the mentioned
Code. Virus type 0] was detected.
* Adapted from Pan-American Foot-and-Mouth Disease Center, Epidemiological
Reports Vol . 4, Nos. 22-24, November 16-30, December 1-15, and 16-31, 1972,
and Vol. 5, No. 1, January 1-15, 1973.
15
HOG CHOLERA PROGRAM STATUS
Program Status ... Since July 1, 1972, the number of "hog cholera free" States
dropped from 46 to 39, with the following States losing their "free" status on
the dates indicated: Nebraska (Aug. 21), Kentucky (Sept. 8), Indiana (Sept. 14),
Ohio (Sept. 14), Tennessee (Oct. 2), Georgia (Oct. 18), and Virginia (Jan. 10,
1973). States can regain "free" status after 6 months with no infection.
New Jersey dropped from Phase IV to Phase III (Dec. 1).
# # # #
HOG CHOLERA SEED VIRUS RECALLED
By December 1, 1972, all hog cholera seed virus vaccine had been recalled from
commercial companies for storage under the supervision of the USDA's Veterinary
Biologies Inspection, Ames, Iowa. Plans call for retention of this material
for 3 years after which a decision will be made concerning final disposition.
Based on recommendations of USAHA and the Secretary's Advisory Committee on
Hog Cholera, with concurrence of States, the issuing of joint State-Federal
hold orders when infected or exposed swine are found moving through markets is
now being implemented. The aim is to stop further movement in the States
involved until tracebacks are completed.
# # # #
AFRICAN SWINE FEVER - HEMADSORPTION TEST
A diagnostician of the State Diagnostic Laboratory, Elba, Alabama, attended
recently the African Swine Fever Short Course at Plum Island Animal Disease
Laboratory, Greenport, Long Island, New York.
During this time, he received instruction in conducting the hemadsorption test
for African swine fever (ASF).
Recently the Alabama State Department of Agriculture and Industries purchased
the necessary equipment and hired the additional help to assist in conducting
the hemadsorption test along with other diagnostic work at the Elba Laboratory.
Arrangements have been made with the other State Diagnostic Laboratories at
Albertville and Auburn to furnish all swine spleens submitted primarily on hog
cholera investigations to the Elba Laboratory for the ASF hemadsorption test.
During the month of December 1972, 18 spleens were tested by the hemadsorption
test for ASF with negative results.
16
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