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Control

Eradication

AGRICULTURE

HANDBOOK N0.119

MARCH 1957

U. S. DEPARTMENT OF AGRICULTURE

Agricultural Research Service
937728

BOVINE BRUCELLOSIS IN THE UNITED STATESRESEARCH, CONTROL, AND ERADICATION

By C, A. Manthei. Animal Disease and Parasite Research

Branch, and C. K. Mingle, Animal Disease

Eradication Branch

CONTENTS

Page

Research 1

Control and Eradication 4

Summary — 9

Motion Pictures on Brucellosis 10

Bovine brucellosis has caused serious economic losses

to the cattle industry in the United States. While the disease

is most prevalent in the predonainantly dairy sections of the

country, it exists from coast to coast and from northern to

southern borders. Moreover, there is probably no disease

of animals at the present time that constitutes a more serious

threat to public health than brucellosis. It is because of the

combined economic and public health aspects of bovine

brucellosis that eradication efforts have received widespread

support in the United States.

Control and eradication of bovine brucellosis, like most

infectious diseases of animals, must be based on the detection

and elimination of infected cattle, the prevention of exposure,

and protection by artificially induced immunity. Over the

years, research has developed the tools that have been used

to successfully connbat this disease.

RESEARCH

One of the outstanding contributions of research toward

successful control of brucellosis has been standardization

of diagnostic procedures. The blood serum agglutination

test has proved to be the most practical and reliable method

of diagnosing bovine brucellosis. Beginning in 1938, major

emphasis was placed on standardizing antigens, procedures,

equipment, and interpretations. These studies included selection of a highly antigenic strain of Bruceila abortus, development of procedures for the selection and maintenance of

smooth colony forms, production of adequate quantities

of the organism, and development of standard methods and

equipment for preparing antigens with a constant sensitivity.

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In 1940, the first standard Bruceila tube and plate antigens

were made available for the diagnosis of brucellosis in livestock. This was followed by adoption of standard equipment

in all State-Federal testing laboratories. Procedures were

then inaugurated to standardize the interpretation of the

tests. Reference serum samples, along with standard tube

and plate antigens, were and still are submitted annually or

semiannually to each official testing laboratory in this country.

Results of tests in each laboratory are returned to the antigen

control laboratory at Beltsville, Md., for compilation and

evaluation. From 1948 to 1955, 91.88 percent of the tube-test

and 91.07 percent of the plate-test interpretations agreed with

the Standard interpretation. Furthermore, there has been 99.12

percent agreement between the tube and the plate tests.

Recent results of research have brought about the official

adoption of a new interpretation of the tube and plate seroagglutination tests for brucellosis in officially calf-vaccinated

cattle 30 months of age or older. The new interpretation

allows the diagnostic titer tobe one dilution higher in officially

calf-vaccinated than in nonvaccinated cattle. By more accurately determining the brucellosis status of 637 calfvaccinated animals examined, this interpretation reduced the

number of reactors by 70 percent and the number of suspects

by 40 percent, and increased the number classified as

negative by 400 percent.

Comparisons of interpretations of the seroagglutinintests

for brucellosis in nonvaccinated and calf-vaccinated cattle

are presented below:

For nonvaccinated cattle For calf-vaccinated cattle

Dilutions Diagnosis Dilutions Diagnosis

1;50 1:100 1:200

Negative

1:50 1:100 1:200

-« - - + * - - Negative

I - - Suspect + I - Suspect

+ - - Suspect + + - Suspect

+ I - Suspect + + I Suspect

+ + ** - Reactor + + + « Reactor

-: Negative

+ : Complete agglutination

*: or less

**: or higher

I: Incomplete agglutination

The milk-ring test is the latest of the diagnostic procedures

to be adopted for the brucellosis control program. The

antigen control laboratory at Beltsville, Md., started producing and distributing milk-ring antigen for official testing

in 1949. Considerable progress has been made since 1949

in developing a standard antigen, procedures for collection

and preservation of milk and cream samples, standard test

procedures, and uniform interpretation of results. The

principal purpose of the milk-ring test is to locate brucellosisinfected herds. This provides for concentration of effort on

eliminating infected animals, and amounts to tremendous
savings in manpower, time, and materials; particularly in

dairy sections of the country.

There are no diagnostic tests capable of accurately

differentiating between serum agglutinin titers caused by

virulent Bruceila abortus and those caused by Strain 19

vaccine. Considerable progress has been made recently,

however, in differentiating between specific agglutinins (those

produced by Bruceila) and nonspecific agglutinins (those

produced by causes other than Brucella) found in the blood

and milk of cattle. When accurate tests are developed, they

will be of considerable aid in correctly classifying aninnals

that show questionable agglutinin reactions.

Much of the research effort, during the last 3 decades,

has been toward the development of an effective immunizing

agent against bovine brucellosis. When the various kinds of

experimental vaccines were evaluated. Strain 19 showed

the best combined qualities of safety, immunogenicity, and

stability. Consequently, vaccination with Strain 19 was

adopted as an integral part of the control program in 1941

and the vaccine has been the only official one in this country

since that time.

Strain 19 is a member of the species Brucella abortus

and has the unique properties of low pathogenicity and

relatively high immunogenicity, which have remained stable

since 1930. All of the available evidence shows that immunity

follows the rapid, complete recovery of cattle from a lowgrade infection produced by Strain 19. Furthermore, the

disease is not transmitted from vaccinated to susceptible

nonvaccinated animals by contact. The desirable characteristics of Strain 19 are maintained by careful selection

of specific colony forms.

Newly selected seed cultures of Strain 19 are supplied

to all biological companies producing vaccine in this country

and to approximately 25 foreign countries every 3 to 4

months. Each lot of vaccine produced in this country is tested

in the vaccine control laboratory for viability, purity, and

colonial characteristics.

Strain 19 vaccine is available either as a liquid or a

dried product. The dried product is more stable than the

liquid one under average environmental conditions. However,

it should always be kept in mind that improper handling of

the dried vaccine can render it useless by causing death

of the Strain 19 organisms.

Immunity produced with Strain 19 vaccine against

brucellosis in cattle is usually relative and seldom absolute.

The degree of immunity induced is directly related to the

response of the individual animal to viable organisms and

this may vary considerably among animals. Furthermore,

it has been repeatedly demonstrated that as the exposure

dose of virulent Brucella abortus increased, the percentage

of vaccinated animals with demonstrable protection decreased.

The large majority of evidence indicates that immunity

produced by calf vaccination with Strain 19 does not decrease
with an increase in age of the animal. Experimental results

also show that any increase in immunity resulting from

revaccination is temporary and does not persist sufficiently

long to be of any practical value.

Accumulated evidence supports 6 to 8 months as the

most desirable age for vaccinating heifer calves with Strain

19. Cattle vaccinated at that age develop an immunity equal

to that produced in cattle vaccinated at older ages. Furthermore, their vaccinal titers recede faster and to a lower

level than those in cattle vaccinated at a later age.

The minimum vaccinal dose of viable Strain 19 organisms

required to produce a serviceable immunity in cattle is

unknown. Controlled experiments to determine the degree

and duration of immunity in cattle vaccinated when between 6

and 8 months of age have not been done with doses of vaccine

smaller than 5 ml. (50 billion viable organisms).

Experimental information shows that the method of injecting vaccine into yearling heifers has little or no influence on

the degree of immunity induced when the dosage of vaccine is

the same. Similar experiments with calves 6 to 8 months of

age have not been reported.

A review of the research on age of vaccination, vaccinal

dosage, and method of administration suggests that subcutaneous vaccination of calves between 6 and 8 months of

age with the 5-ml. dose of Strain 19 vaccine is preferable.

Moreover, loss of viability through improper handling of

vaccine further recommends the 5-ml. dose which provides

added insurance that animals will receive adequate numbers

of viable organisms to produce a serviceable immunity.

Treatment of brucellosis in cattle has notbeen successful.

Practically all of the antibiotics and the newer drugs have

been tried, some of which have a tendency to depress the

infection temporarily. After treatment is stopped, infection

usually returns to its normal course. Many alleged cures have

gained considerable prominence by being used in herds when

symptoms are normally subsiding.

A considerable part of future research will be concerned

with improvement of methods for classifying the species of

Bruceila, increasing the specificity of diagnostic procedures,

and developing new and improving pre sent immunizing agents.

CONTROL AND ERADICATION

The campaign to eradicate brucellosis from cattle in

the United States began during the summer of 1934. From

the beginning, this program has been developed as a cooperative State-Federal undertaking designed to eliminate,

as quickly as possible, the primary exposure sources,

nannely, infected animals. Although a great deal was accomplished during the early years of the project by the

te st-and-slaughter method, it soon became apparent that

complete eradication by this procedure alone would be

difficult to accomplish on a nationwide scale. Regardless

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of the procedures employed, it has been repeatedly demonstrated that the progress made in various areas of the

country is far more closely related to the thoroughness

with which the procedures are applied than with actual

nnethods themselves.

Variations in the types of herds infected with brucellosis,

differences in the character of the disease as it affects

various herds, and the degree and length of time infection

has been present are important factors to be considered in

the selection and application of appropriate means of control.

One of the greatest dangers connected with a test-andslaughter program is the matter of replacenaents. Owners

of herds on a rigid testing program are extremely vulnerable

from at least two directions. First, they face the danger of

introducing infection through newly purchased stock even

when the best precautions are exercised. Secondly, the

introduction of highly susceptible animals from herds that

have been free of the disease for several years provides

fertile ground for perpetuating any residual infection that

might remain on the premises.

Approximately 33 million cattle were tested during the

first 5 years of the program and the percentage of reactors

was reduced from 11.5 in 1935 to 2.5 in 1939. It soon becarne

evident that the most favorable time to eradicate brucellosis

from herds is after clinical manifestations have subsided.

This, of course, is impractical in nationwide program

operations.

Previous experiences with test and elimination of reactors already had emphasized the need for an immunological agent. Consequently, the approval of Strain 19 vaccine

in 1941 was an important step in complementing available

control and eradication procedures. As might be expected,

vaccination was extremely popular in many sections of the

country and each year since it became a part of the official

program there has been a marked increase in its use. For

the 5-year period extending from 1941 through 1945, approximately 2 million calves were vaccinated officially. There is

no question, of course, about the value of Strain 19 vaccine

when it is used under appropriate conditions. The fact that

the protection afforded by this product is usually relative,

emphasizes the importance of limiting exposures of vaccinated animals, through the adoption of approved aninaal

husbandry and sanitary practices.

Since adoption of the ring test in 1952, this procedure

has proved extremely valuable in screening dairy-type

herds for presumptive evidence of Bruceila infection. Where

moderate to low degrees of infection exist, counties can be

ring tested at approximately 10 percent of the cost of blood

testing the same areas. Both milk and cream samples can

be examined by this method. Insofar as its efficiency is

concerned, it has been found that the ring test locates

around 90 percent of the herds in which one or more Brucella-

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infected animals are in production. There seems to be a

psychological aspect associated with ring testing that encourages livestock owners to become actively interested

in eradicating brucellosis frona their herds.

Progress in the bovine brucellosis eradication efforts

during the years before 1947 was greatly handicapped by

lack of uniformity in operations in different parts of the

country. In order to correct this situation, the former Bureau

of Animal Industry took steps to encourage the establishment

of uniform control and eradication practices. Sufficient

interest was stimulated through discussions with interested

groups to result in the adoption of uniform bovine brucellosis

eradication procedures at the December 1947 meeting of the

United States Livestock Sanitary Association. These recommendations are an integral part of the State-Federal memoranda of understanding relative to the cooperative brucellosis

eradication project.

The design of these recommendations was predicated on

the imiportance of providing reasonable flexibility for handling

the brucellosis problem under varying herd conditions.

Essentially they consist of four separate plans which are

as follows:

Plan A - Test-and-slaughter, with or without calf vaccination.

This plan has eradication as its immediate goal and

is the method of choice where the incidence of infection

is low and herds are self-contained. In the United States,

about 7 out of 10 infected herds can be freed of

brucellosis by 2 complete herd tests and prompt

removal of reacting aninaals.

Plan B - Test, calf vaccination, temporary retention

of reactors.

The plan is designed to enable the owners of heavily

infected herds to work out of a difficult brucellosis

situation in a gradual manner, thereby avoiding serious

economic shock. This procedure permits reactors to

be held in quarantined herds for periods not to exceed

3 years. Plan B has been widely used throughout the

country and for the most part has worked effectively

as a stepping stone toward Plan A and eventual

eradication.

Plan C - Calf vaccination without test of any part of the

herd.

This plan was developed primarily to encourage the

range cattle industry to recognize the brucellosis

problem and to initiate some action toward its solution.
Plan C is confined to herds where the movement of

animals is allowed only through special permits issued

by State Livestock Sanitary Officials.

Plan D - Adult vaccination.

This was included in the procedures to counteract

unofficial vaccination of adult cattle. Under present

conditions, there is every reason to discourage this

practice in the United States. Fortunately it has

declined steadily during the past few years. In the

presence of so-called ''infection storms/* a condition

usually existing in herds where vaccination is requested, most of the animals already are exposed.

Plan D requires the testing of entire herds, with

vaccination of adults confined to nonreactor cattle

that have been tested within the previous 10 days.

This plan is available only on written approval of the

State-Federal cooperating agencies.

From July 1934, to June 30, 1955, a total of nearly 12

million herds, representing approximately 142 million cattle,

were tested for brucellosis. Over the same period, the

indicated animal infection dropped from 11.5 to 2.6 percent.

This 2.6 percent animal infection rate represents evidence of

the disease in 14.6 percent of the herds tested. During the

first 7 years of the program, when yearly testing volumes

remained high, there was a decline each year in the percentage

of reactors disclosed. With personnel problems developing in

1942, testing declined and the percentage of reactors started

to rise, reaching a secondary peak of 5 percent in 1947. From

this point on, there again has been a consistent reduction in

animal infection rates.

Greatly increased interest in brucellosis eradication is

being displayed by various groups, including the livestock

industry, the veterinary profession, livestock sanitary officials, and the general public. This interest has been reflected

in the growing volume of official work performed. For the

12-month period ending June 30, 1955, more than 14 million

cattle were tested for brucellosis in the United States. This

represents an increase of 58 percent over the number of

tests made in 1954. During the 15-year period (1941-55)

a total of 25.7 million calves were officially vaccinated with

Strain 19. Since its approval in 1941, the use of Strain 19

has increased each year, reaching an all-time high of over

four million calves vaccinated in 1955. In most sections of

the country where vaccine has been extensively used, there

is a significant increase in the volume of blood testing.

The maintenance of brucellosis-free areas has constituted

a rather serious problem. With the advent of the milk and

cream ring test, this difficulty has been largely overcome in

dairy sections of the country. By conducting semiannual

ring tests at milk and cream collecting stations, it is possible

to detect centers of infection early enough to limit spread of

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the disease. Since it became a part of the official program

in 1952, approximately 3 million herds, representing an

estinnated 58 million cattle, have been ring-tested in 38 States

through the fiscal year 1955,

The Congress of the United States has made available

additional funds for use in accelerating the brucellosis

eradication project during the fiscal years 1955 and 1956,

This action could not have been taken at a more appropriate

time, as current interest in eradicating the disease has

never been greater. It has been possible to expand operations in most sections of the country far more rapidly than

was expected. The fact that the new program called for the

restoration of former maximum indemnity payments of

25 dollars for grade animals and 50 dollars for purebreds

to owners of cattle destroyed because of brucellosis has

also been an important contributing factor. Also, the new

interpretation of blood agglutination reactions in officially

calf-vaccinated animals has further encouraged wider participation.

At the inception of the expanded program, it was realized

that the personnel requirements would have to be met through

the employment of practicing veterinarians. This being the

case, a system was developed for paying cooperating veterinarians on a per-head or per-herd-and-per-head basis. The

response of the veterinary profession in the newprogram has

been excellent.

Table 1 shows the increased volume of brucellosis

eradication activities for fiscal year 1955 over fiscal year

1954,

TABLE 1.--Comparative Brucellosis Activities Immediately Before and After Inauguration

of Expanded Program

Fiscal Year

Activities

1954 1955

Change

Blood tests

Herds

Number

696.207

9,002.109

932.003

16,633.034

3.999,101

^154,990

Number

984,541

14,186.241

1.200.898

20.444.994

4.381,397

2 302,812

Percent

41 +

Cattle .,.., , .,, 58 +

29 +

Ring tests

Herds

Cattle , 23 +

Vaccinations , ,..,. 10 +

Reactors slaughtered,,,.,,...,.,,.,,,,. 90 +

^ 65 percent

2 82.9 percent

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The second year of the accelerated program is showing

a continued high level of brucellosis operations« From

July 1 through December 31, 1955, there was a 13 percent

increase in the nunnber of calves vaccinated, a 56 percent

increase in the number of cattle tested, and a 33 percent

increase in the number of reactors slaughtered, over that

recorded for the same period in 1954, It seems highly

significant that approximately 96 percent of the reactors

disclosed by testing are now being slaughtered imnnediately.

SUMMARY

Major contributions of research in the development and

progress of the control and eradication of bovine brucellosis

are as follows:

1. Development of a standard blood serum agglutination

test.

2, Developnnent of information leading to the re comnaendation and adoption of a new interpretation of the

blood serum agglutination test for cattle officially

vaccinated as calves with Strain 19 vaccine.

3. Standardization of milk ring antigen, testing procedures

and interpretation.

4, Developnment of Strain 19 vaccine, and standardization

of methods for its production and administration have

been responsible for providing a serviceable immunizing product against bovine brucellosis.

Highly encouraging progress is being made in the campaign to eradicate bovine brucellosis in the United States. The

following points are considered important in this regard:

1. Since 1935, the percentage of brucellosis reactors

disclosed through blood agglutination testing has been

reduced from 11.5 to 2.6. A corresponding reduction

has occurred in the percentage of infected herds. For

the fiscal year 1935, 36.2 percent of the herds tested

were found to be infected. As of December 31, 1955,

this figure had been reduced to 13.8.

2. The adoption of Uniform Methods and Rules has been

a major factor responsible for the favorable progress

made during recent years in the bovine brucellosis

eradication campaign.

3. Extensive field experience has shown that an eradication program based upon the intelligent use of a

standardized blood serum agglutination test, the milk

and cream ring test, and Strain 19 vaccine can be

effectively carried out.

4. Full support of the livestock industry, the veterinary

profession and the general public is essential to the

successful conduct of a brucellosis eradication campaign.

If the current intensified effort can be maintained, it is

possible that the incidence of bovine brucellosis throughout

the United States can be reduced to 1 percent or less within

the next five years.
MOTION PICTURES ON BRUCELLOSIS

The United States Department of Agriculture has released

the following motion picture films on Brucellosis. They are

available for loan from the Land-Grant College Filna

Libraries, or you may write the Motion Picture Service, Office of Information, U. S. Department of Agriculture«

1. Battling Brucellosis, 16 mm, color film, 20 minutes,

released 1946,

2. The Triple Threat of Brucellosis, 16 mm,, color, also

black and white, 27 minutes, released 195L

3. Brucellosis Ring Test, 16 mm,, color, 5-3/4 minutes,

released 1957.

For sale by the Superintendent of Documents, U. S. Government Printing Office

Washington 25, D. C. - Price 10 cents

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