Potential Bacillus anthracis Risk Zones for Male Plains Bison (Bison bison bison) in Southwestern Montana, USA

ABSTRACT A re-emergence of anthrax, a zoonosis caused by the long-lived, spore-forming Bacillus anthracis, occurred with a multispecies outbreak in southwestern Montana, US in 2008. It substantially impacted a managed herd of about 3,500 free-ranging plains bison (Bison bison bison) on a large, private ranch southwest of Bozeman, with about 8% mortality and a disproportionate 28% mortality of mature males; a similar high rate occurred in male Rocky Mountain elk (Cervus canadensis nelson). Grazing herbivores are particularly at risk for anthrax from ingesting spore-contaminated soil and grasses in persistent environmental reservoirs. We predicted areas of mature male bison habitat preference on the landscape by using GPS collar data and a resource selection function model using environmental covariates. We overlaid preferred areas with ecologic niche, model-based predictions of B. anthracis environmental reservoirs to identify areas of high anthrax risk. Overlapping areas were distributed across the ranch ...