Bovine Tuberculosis

Tuberculosis (TB) is a contagious disease of both

animals and humans. It is caused by three specific

types of bacteria that are part of the Mycobacterium

group: Mycobacterium bovis, M. avium, and M.

tuberculosis.

Bovine TB, caused by M. bovis, can be 

transmitted from livestock to humans and other 

animals. No other TB organism has as great a host

range as bovine TB, which can infect all 

warmblooded vertebrates. M. avium can affect all

species of birds, as well as hogs and cattle.

M. tuberculosis primarily affects humans but can also

be transmitted to hogs, cattle, and dogs.

Bovine TB has affected animal and human health

since antiquity. Once the most prevalent infectious

disease of cattle and swine in the United States,

bovine TB caused more losses among U.S. farm 

animals in the early part of this century than all other

infectious diseases combined. Begun in 1917, the

Cooperative State–Federal Tuberculosis Eradication

Program, which is administered by the U.S.

Department of Agriculture's (USDA) Animal and Plant

Health Inspection Service (APHIS), State animal

health agencies, and U.S. livestock producers, has

nearly eradicated bovine TB from the Nation's livestock population. This disease's presence in humans

has been reduced as a result of the eradication program, advances in sanitation and hygiene, the discovery of effective drugs, and pasteurization of milk.

The Disease

In general, disease-causing mycobacteria live

only a few weeks outside a host's body because they

cannot tolerate prolonged exposure to heat, direct

sunlight, or dry conditions. Under cold, dark, and

moist conditions, the organisms can survive longer.

Mycobacteria do not grow outside of a host

except in cultured media, where they multiply approximately once every 20 hours. Because of this relatively slow rate of growth, the disease usually takes

many months to develop. In some instances, the

organisms lie dormant within the host's body for its

lifetime, both in animals and in humans, without 

causing progressive disease.

Bovine TB is a chronic disease, seldom becoming

apparent until it has reached an advanced stage in

cattle, captive cervids, and swine. Some infected

livestock seem to be in prime condition, showing no 

evidence of infection until they are slaughtered, yet

they may be found so seriously infected during

slaughter inspection that their carcasses must be

condemned.

TB Transmission

Bovine TB can be transmitted from animals to

humans and vice versa. Although young animals and

humans can contract the disease by drinking raw

milk from infected dams, the most common means of

transmission is through respiration. Invisible droplets

(aerosols) containing TB bacteria may be exhaled or

coughed out by infected animals and then inhaled by

susceptible animals or humans. The risk of exposure

is greatest in enclosed areas, such as barns.

Inhalation of aerosols is the most common route of

infection for farm and ranch workers and veterinarians who work with diseased livestock. Livestock also

are more likely to infect each other when they share

a common watering place contaminated with saliva

and other discharges from infected animals. Calves,

hogs, and humans can contract bovine TB when they

drink unpasteurized milk from infected cows.

Diagnosis

TB lesions may be found in any organ or body

cavity of diseased animals. In early stages of the 

disease, these lesions are difficult to find, even during

post mortem examination. But in later stages, the

nodules or lumps caused by bovine TB become very

evident in the lungs and associated lymph nodes and

in the lymph nodes of the head and intestinal tract.

Lesions may also appear in the abdominal organs,

reproductive organs, nervous system, superficial

body lymph nodes, and bones.

Humans and animals with TB develop an immune

response, which can be detected by the tuberculin

skin test. Tuberculin is a sterile laboratory product

made by growing TB bacteria, killing them with heat,

removing them from the substance on which they

were grown, and properly diluting and preserving the

remaining mixture. About 72 hours after tuberculin is

injected into animals affected with TB, a characteristic

swelling reaction appears at the point of injection.

This reaction is a positive test result, indicating 

exposure to one type of mycobacteria.

Further diagnostic methods are necessary to

confirm the presence of bovine TB. In humans, these

tests include chest x rays and sputum cultures. For

animals, the comparative cervical tuberculin test,

serological tests, post mortem examinations, and

other laboratory procedures are used.

Factsheet

 

 
 

APHIS
The course of treatment for humans with bovine

TB takes 6 to 9 months, and the success rate 

following treatment is more than 95 percent. In livestock, bovine TB can be controlled within an affected

herd through regular testing and slaughter of any 

single animal that tests positive until the entire herd

tests negative for this disease. However, because

there is no method available to ensure that bovine TB

has been eliminated from an affected herd, APHIS 

recommends herd depopulation.

Control and Eradication

The most effective way of handling the problem of

bovine TB in humans is to eradicate it in livestock. At

the start of the cooperative eradication program at the

beginning of this century, all cattle herds were 

systematically tested, and all reactors were sent to

slaughter. Federal and State agencies shared in the

payment of indemnities. Premises were cleaned and

disinfected after infected cattle were removed. As a

result of this program, the reactor rate in cattle was

reduced from about 5 percent to currently less than

0.02 percent. Consequently, the incidence of human

TB caused by M. bovis also decreased significantly.

The resurgence of human TB in recent years is 

attributable to M. tuberculosis.

Today, with a very low rate of bovine TB, the most

efficient way of finding the disease is through a

nationwide surveillance program in slaughter plants.

State or Federal meat inspectors check the glands

and organs of cattle for signs of TB. If these 

inspectors find lesions indicative of TB infection, 

tissue samples are sent to APHIS' National Veterinary

Services Laboratories in Ames, IA, for confirmation. If

the laboratory confirms that the lesions are the result

of bovine TB, an exhaustive attempt is made to trace

the infected livestock back through market channels to

the originating herd, which is then tuberculin tested.

If the herd of origin is diagnosed with M. bovis,

every effort is made to eliminate all animals in the

herd. Indemnities, as available, are paid to help 

compensate owners for their losses. If the herd 

cannot be depopulated, it is held under quarantine

and tested repeatedly until all evidence of infection is

eliminated.

Veterinary epidemiologists also attempt to determine the date the herd was probably infected. They

then undertake a concerted effort to trace all cattle

that moved into or out of the affected herd to try to

find out where the disease came from and where it

might have gone.

Area Accreditation

For a State to be accredited free of bovine TB,

there must have been no confirmed cases of the 

disease for at least 5 years, and the State must have

a set of stringent laws and regulations governing livestock dealers. The State must also maintain surveillance of cattle in marketing channels and require that

records be kept that would allow animal health 

officials to trace infected animals back to their source.

Herd Accreditation

Livestock owners may achieve accredited TB 

status for their individual herds by following the

"Accredited Herd Plan." Details can be found in the

publications, "Bovine Tuberculosis Eradication,

Uniform Methods and Rules" (UM&R) and

"Tuberculosis Eradication in Cervidae, UM&R."

For a herd to qualify as accredited, a negative

finding on two annual TB tests must be attained for all

cattle over 24 months of age and cattle of any age

that are not natural additions to the herd. Deer and

elk herds must test negative for 3 consecutive years.

To qualify and continue as an accredited herd, livestock must be tested annually within 10 to 14 months

of the anniversary of the original test. Livestock from

any herd in an accredited free State may be added to

an accredited herd without a qualifying test.

What You Can Do

As a livestock producer—dairy, beef, deer, or

elk—there are certain things you can do to protect

your animals from TB.

The first and most important is to be aware that

TB is not gone! Too many farmers falsely believe that

TB in cattle has already been eradicated. Remember

that this chronic disease will continue to be a threat to

animal health until the last infected animal has been

eliminated.

So, to be safe, have your livestock tested for TB

by an accredited veterinarian to make sure the disease isn't present in your herd. Other tips for preventing TB infection are as follows:

• One of the best ways to avoid TB—and other 

diseases, too—is to keep a closed herd. Doing 

so involves raising your own replacement stock.

If this system isn't practical for you, demand that 

sellers give you historical health information 

about the herd of origin. It's best to buy from 

accredited TB-free herds.

• If you cannot obtain health histories, make sure 

any prospective livestock are tested before pur

chase. Isolate these animals and have them 

retested 60 days later by an accredited 

veterinarian.

• Maintain fences in good repair to keep your 

animals from mingling with neighboring animals.

• And, finally, cooperate with State and Federal 

animal health officials who are carrying out 

traceback investigations.
For more information about bovine TB or for

copies of the UM&R's, contact:

Joseph S. Vantiem

USDA, APHIS, Veterinary Services

Animal Health Programs

4700 River Road, Unit 36

Riverdale, MD 20737–1231

Telephone (301) 734–6954

or visit our Web site at www.aphis.usda.gov/vs.

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture