Descriptive epidemiology of detected anthrax outbreaks in wild wood bison (Bison bison athabascae) in northern Canada, 1962-2008.

We inventoried and assessed historical anthrax outbreak data from 1962-2008 in wild wood bison (Bison bison athabascae) in Wood Buffalo National Park and the Slave River Lowlands (SRL), Northwest Territories, Canada. We compared these results with a 2010 outbreak in the SRL. Anthrax outbreaks have occurred in 12 of the years between 1962 and 2008 in wild wood bison with 1,515 anthrax deaths detected. The average number of carcasses found each outbreak year was 126 (range 1-363), though local averages varied. The numbers of animals found dead per outbreak declined over the past four decades. Outbreaks varied in duration from 16-44 days (average length 25.5 days). The length of an outbreak was not a determinant of the number of dead bison found, but outbreaks starting in July had more deaths than those staring in June. Males were more likely to be detected in an outbreak, outbreaks were likely not random events, and there was no relationship between outbreak size or length and location. Future surveillance activities may benefit from targeting bulls and planning surveillance activities for more than 3 wk after outbreak detection. Coordinating data collecting and recording efforts between jurisdictions may overcome historical challenges in inconsistent record keeping.