A review of anthrax in Canada and implications for research on the diseasein 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 of ten associated with pastures contaminated by effluent from textile industri es 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 t he disease have been reported almost er;exclusively in cattle in the wester n prairie provinces. Between 1962 and 1993, nine anthrax epizootics have be en recorded in the bison herds of the Northwest Territories and northern Al berta resulting in the deaths of at least 1309 animals. During the nothern epizootics there has been a strong sex bias in mortalities with the majorit y of carcasses being sexually mature bulls. The northern epizootics occur d uring drought conditions in the late summer, preceded by a wet spring, and end with the arrival of coolers Weather. It has been hypothesized that stre ss factors associated with these meteorological conditions coupled with bre eding stress during the late summer rut may predispose the bulls to infecti on. Alternatively, the meteorological conditions may work to concentrate an thrax spores in the environment into low lying mallows preferentially utili zed by the bulls. Recent genetic analyses of Bacillus anthracis isolates fr om Canada and the United States hale identified that, while closely related to isolates from domestic outbreaks, isolates from northern bison epizooti cs 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 anthra x from cattle to the indigenous bison.