Factors affecting apparent prevalence of tuberculosis and brucellosis in wood bison

1. Bison (Bison bison) abundance in Wood Buffalo National Park, Canada, declined from in excess of 10 000 bison in the late 1960s to a low of 2200 bison in the late 1990s. 2. Bovine tuberculosis (Mycobacterium bovis) and brucellosis (Brucella abortus), were introduced to Wood Buffalo National Park in the late 1920s. As each of these pathogens have the potential to reduce survival and reproduction in bison, they are suspected to have played a role in the decline in bison abundance. 3. We live-captured bison for disease testing in February and March of 1997, 1998 and 1999. Forty-nine percent tested positive for tuberculosis (i.e. were positive on the caudal fold test and/or fluorescent polarization assay, n = 342). Further, 30.9% of bison were seropositive for brucellosis (i.e. agglutinated in the buffered-plate antigen test and had a titre of 1 : 5 in the complement fixation test or had a titre of greater than or equal to 1 : 10 in the complement fixation test, n = 346). Prevalence for both diseases increased with age and males were more likely to test positive for tuberculosis. Prevalence of either disease did not appear to be directly related to density of bison, as prevalence rates were not greater in the high density Delta population than the lower density Hay Camp and Nyarling River populations. 4. Comparison of our results to previous brucellosis and tuberculosis surveys in Wood Buffalo National Park indicates that prevalence of neither pathogen is a direct function of bison density. These pathogens are endemic within the bison population of the park.