Animal HealthDiseasesTuberculosisEpidemiology

Tuberculosis Epidemiology

The incidence and distribution in Montana and elsewhere, along with the information regarding the spread of the disease.


Mode of Transmission
TB can be transmitted from animals to humans and vice versa.

The most common mode of transmission is through respiration. Invisible droplets (aerosols) containing TB bacteria may be exhaled or coughed out of infected animals and then inhaled by susceptible animals or humans. The risk of infection increases in enclosed areas, such as barns, for both humans and livestock. Livestock may also 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.

Isn't TB Gone?
The United States has come close to eliminating bovine tuberculosis (TB). Before USDA launched a tuberculosis eradication program in 1917, 5 percent of the nation's cattle were infected. That figure dropped to 0.015 percent by 1990.

But recent developments demonstrate that Mycobacterium bovis, the causative agent of bovine TB, is far from eliminated. In Michigan, an outbreak among white-tailed deer that may have started in livestock has spread to at least 20 cattle herds. Importation of Mexican feeder cattle has sparked concerns in Texas, where two herds have tested positive. In both states, the disease has led to economic woes and forced depopulation of infected herds.

In year 2000, the Secretary of Agriculture declared an emergency under which he authorized the transfer of $44 Million from emergency contingency funds to USDA’s Animal and Plant Health Inspection Service (APHIS) to expand the TB eradication program in the United States. More about this...

APHIS has identified four main TB threats. They are:

  1. TB is being transmitted to livestock from infected wildlife, especially free-ranging deer.
  2. Transmission of TB from infected captive deer and elk threatens U.S. cattle and other livestock.
  3. The U.S. cattle population is being threatened by recurring TB infection of dairy herds along U.S. Mexican border (in the El Paso, TX, area).
  4. A decline in testing for TB in recent years also threatens to allow the spread of the disease in the United States.

Animal Health Bureau

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Contact Information

Department of Livestock
Animal Health Bureau
PO Box 202001
Helena, MT 59620-2001
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