A review of anthrax in Canada and implications for research on the disease in northern bison.

During the first half of the century, the majority of anthrax outbreaks in Canada occurred in the southern portions of Ontario and Quebec and were often associated with pastures contaminated by effluent from textile industries dealing with imported animal materials. In 1952, introduction of Federal regulations requiring disinfection of these materials greatly reduced the incidence of anthrax in eastern Canada. Since 1962, domestic outbreaks of the disease have been reported almost exclusively in cattle in the western prairie provinces. Between 1962 & 1993, nine anthrax epizootics have been recorded in the bison herds of the Northwest Territories and northern Alberta resulting in the deaths of at least 1309 animals. During the northern epizootics there has been a strong sex bias in mortalities with the majority of carcasses being sexually mature bulls. The northern epizootics occur during drought conditions in the late summer, preceded by a wet spring, and end with the arrival of coolers weather. It has been hypothesized that stress factors associated with these meteorological conditions coupled with breeding stress during the late summer rut may predispose the bulls to infection. Alternatively, the meteorological conditions may work to concentrate anthrax spores in the environment into low lying wallows preferentially utilized by the bulls. Recent genetic analyses of Bacillus anthracis isolates from Canada and the United States have identified that, while closely related to isolates from domestic outbreaks, isolates from northern bison epizootics form their own distinct strain. This suggests that the establishment of anthrax in northern Canada was a singular event that occurred prior to the first recognized epizootic in 1962. A review of the agricultural history of northern Canada has identified several situations in the first half of the century which may have provided the opportunity for the transfer of anthrax from cattle to the indigenous bison.