INVESTIGATION, CONTROL AND EPIZOOTIOLOGY OF ANTHRAX IN A GEOGRAPHICALLY ISOLATED, FREE-ROAMING BISON POPULATION IN NORTHERN CANADA

In July 1993 anthrax caused significant mortality in an isolated, free -ranging population of bison (Bos bison athabascae) west of Great Slav e Lake in the Northwest Territories, There was no previous record of a nthrax in this area, An emergency response was undertaken to reduce th e scale of environmental contamination and dissemination of anthrax sp ores and hence to reduce the likelihood of future outbreaks. One-hundr ed-and-seventy-two bison, 3 moose (Alces alces), and 3 black bear (Urs us americanus) carcasses were found, Visual detection of carcasses was enhanced with the use of an airborne, remote infrared sensing camera mounted externally on a helicopter, Fifty-five percent of the carcasse s were located in forested or shrub-covered sites where detection woul d not have been likely without the thermal imaging equipment, Carcasse s were disposed of by incineration and the sites were decontaminated w ith formaldehyde. Application of formaldehyde to carcasses prevented s cavenging, The outbreak occurred after a prolonged period of drying be tween April and mid-July 1993 which followed several successive years of flooding of bison habitat, The ''spore concentration hypothesis'' p rovides the most conservative explanation for the occurrence of anthra x under the observed conditions.