Tuberculosis in wildlife poses threat to cattle, disease-free status

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Tuberculosis is still present in Canada. 


Bison in Wood Buffalo National Park and elk in Riding Mountain National Park are infected with the disease, and nearby cattle herds are at risk of contracting it from these potential sources of infection.


The bacteria, Mycobacterium bovis, causes chronic, debilitating infections in a wide variety of domestic and wild animals. The characteristic tuberculosis lesions are large, semi-solid, pus-filled lymph nodes and growths in the lungs.


Both the disease and the issues surrounding it are long-lived and difficult to manage. 


Tuberculosis was controlled starting in 1896, and eventually eradicated from cattle in the 1980s through an expensive control program. 


Positive herds were culled following testing. Infections detected at slaughter were traced back and the herds eliminated. 


Tuberculosis in cattle was discovered in Alberta in 2001 and British Columbia in 2007, but the source of these infections was not determined. 


Eradication has been achieved in Canadian cattle, but infected wildlife threatens our disease-free status. 


The situation in Canada is not unique. Wildlife reservoirs of tuberculosis are present elsewhere, including possums in New Zealand, badgers in the United Kingdom and white-tailed deer in Michigan.


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In humans, it is impossible to tell whether cattle or other humans are the source of infection without sophisticated molecular diagnostic testing. Both look similar. 


Tuberculosis was a flagship disease in the public health movement and provided the major incentive for milk pasteurization, which kills the bacteria. 


Bovine tuberculosis was passed from unpasteurized milk to people, mainly children, who went on to develop oozing lymph nodes in the neck. Tuberculosis, especially in the lungs, kills people if left untreated. 


Festering in Alberta and Manitoba, this disease continues to threaten Canada’s cattle herd, exports and ultimately human health. 


Wood bison in Wood Buffalo National Park became infected with tuberculosis when the Canadian government made the controversial decision in the 1920s to move 6,000 Plains bison from Buffalo National Park wear Wainwright, Alta. 


Not only did the two subspecies interbreed to create hybrids but they are also suspected of transmitting tuberculosis and another infectious disease, brucellosis. 


A survey of bison hunted near Wood Bison National Park in the early 1980s found 21 percent were infected. A more recent study found more than 50 percent of bison tested had been exposed to tuberculosis. 


First detected in elk near Riding Mountain National Park in 1992, tuberculosis has since been found in less than one percent of elk tested in the area. 


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Neighbouring cattle have tested positive, presumably picking up the infection from elk. Extensive testing in the area still occurs. 


Treatment and vaccines don’t exist for controlling this disease in cattle and wildlife. 


Who is responsible for these smouldering clusters of disease? The answer is complex and partially explains why eradication has not been achieved. 


Parks Canada has jurisdiction over animals within the park. In Riding Mountain, elk outside the park are considered wildlife and fall under the jurisdiction of provincial wildlife. 


In Alberta, however, bison are classified as domestic animals, which means wild bison that wander outside national parks are treated as livestock at large. 


The Canadian Food Inspection Agency is primarily concerned with potential exposure and testing of domestic animals that may contract tuberculosis from wildlife. 


Muddying the waters even further are special interest groups, including conservationists, First Nations and hunters. 


The current policy of neglect is not a solution. Co-operation among government, the cattle industry and other interest groups is necessary for conclusive action to occur. Without treatment or vaccination, culling these diseased animals is the only reasonable solution. 


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Abundant healthy bison and elk populations exist in other parts of the country that can be used to replenish the parks. Action should be taken before more cattle, or worse, people become infected.

Dr. Jamie Rothenburger is a veterinary pathology resident at the Western College of Veterinary Medicine, University of Saskatchewan.