Bovine Tuberculosis (Mycobacterium bovis)
Bovine Tuberculosis is a contagious, debilitating disease of both humans and animals. It is caused by the bacterium Mycobacterium bovis (M. bovis), part of the Mycobacterium complex which also includes M. tuberculosis and M. avium. The primary site of infection is the lymph nodes, but spread to other organs such as the lungs will occur as the disease progresses. Clinical signs of the disease include weakness, loss of appetite, weight loss and fever. Bovine TB is a chronic disease, and infected animals may take several years to develop clinical signs or may show no evidence of infection until they are sent to slaughter.
Cattle are the usual host for M. bovis, but bovine TB can be transmitted to humans as well as other animals such as swine, bison and cervids (deer and elk). The bacteria do not survive exposure to heat, sunlight or dry conditions, and do not replicate outside the host. People at greatest risk are those in direct and prolonged contact with infected animals, such as farmers, farm workers and veterinarians. The most common means of contracting the disease is through inhalation of aerosols containing TB bacteria exhaled or coughed out by an infected animal. The risk of exposure is greatest in enclosed areas such as barns. Other methods of exposure include the drinking of unpasteurised milk from an infected cow and the sharing of common water or feed sources.
Because the disease in cattle may not be clinically evident, even in advanced stages, diagnosis is often made upon post mortem examination at slaughter. Nodular lesions may be found in any organ or body cavity, but are usually seen in the lungs and associated lymph nodes of the head, respiratory and gastrointestinal tracts.
In Canada, Bovine Tuberculosis is a reportable disease under the Health of Animals Act. When a veterinarian reports a suspected case, the Canadian Food Inspection Agency follows a strict testing and eradication program. Preliminary diagnosis of TB infection is through the tuberculin skin test. This confirms exposure to a type of Mycobacterium but further diagnostic methods are necessary to confirm the presence of bovine TB. In humans, this includes chest x-rays and sputum cultures. For cattle, a diagnosis is normally made through post mortem examination and tissue culture, although bacterial culture to confirm the presence of M. bovis can take up to 12 weeks. Once bovine TB is confirmed, all infected and exposed animals are destroyed with federal compensation. After the premises have been depopulated, the owner is responsible for cleaning and disinfecting the facility under CFIA guidance.
Further information on Bovine Tuberculosis is available on the internet at the CFIA website and the USDA website.
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