Tuberculosis (TB) is a chronic infectious disease of almost all vertebrates, including humans. Cattle or bovine tuberculosis is caused by the Mycobacterium bovis bacterium.
An infected animal releases the bacteria into the air when coughing. Cattle become infected when they inhale these bacteria or take them in through feed. Cows with infected udders can also secrete the bacteria into their milk. Suckling calves drinking the infected milk can contract TB in this way.
- Most infected cattle show no clinical symptoms.
- In cases of chronic and widespread infection within the body, the animal may gradually become thin, with a dull coat and poor appetite. In the case of severe lung lesions, a single suppressed, moist cough and difficult breathing may occur.
- Other symptoms such as mastitis, reduced fertility, continuous bloat or enlarged superficial lymph glands may also be present.
Bovine TB can be diagnosed directly through laboratory tests, but indirect diagnoses by means of the intradermal tuberculin test (skin test) is most frequently used in South Africa. This test is highly reliable when performed by an experienced tester.
Bacteria or saliva from cattle with bovine TB can contaminate pastures, water troughs, mineral and feed-licks, making these a source of infection for other animals, especially buffalo and kudu. This process is enhanced by moist, cool conditions, which help the bacteria survive outside the body.
Predators such as lion and leopard feeding on infected buffalo and kudu carcasses can, in turn, pick up the infection. Cats around milking parlours can serve as a constant source of reinfection of bovine tuberculosis in a dairy herd, if they are given unpasteurised milk from infected udders.
Government is following a ‘slaughtering out’ policy for infected cattle under the Tuberculosis Eradication Scheme. The purpose of this is to eradicate the disease in South Africa. Participation in the scheme is voluntary, except for herds in which infection is diagnosed.
In addition, the pasteurisation of milk for human consumption is compulsory in South Africa to prevent the spread of bovine TB and other zoonotic diseases to humans (see panel).
Movement control of tuberculosis-infected cattle, buffalo and other game is also aimed at preventing further spread of the disease. It should be remembered that dry conditions, as well as direct sunlight, can help destroy the bacteria.
For further information, contact your nearest animal health technician or state/private vet.
Source: Directorate Communication Services, department of agriculture.
01 July 2016