Risks of Brucella abortus spillover in the Greater Yellowstone area.

Recurrent spillover of Brucella abortus from wildlife reservoirs to domestic cattle in the Greater Yellowstone Area (GYA) has prevented the United States from completely eradicating bovine brucellosis. Risks to cattle are a function of the size and location of wildlife and livestock populations, the degree and nature of spatio-temporal interactions between the various hosts, the level of disease in wildlife, and the susceptibility of livestock herds. While the brucellosis prevalence in wild, free-ranging GYA bison (Bison bison) is high, current management actions have successfully limited contact between bison and cattle. Under current management practices, the risks to cattle in the GYA are predominantly from wild elk (Cervus elaphus). Intra- and inter-species transmission events, while uncommon, are nevertheless crucial for the maintenance of brucellosis in the GYA. Future management actions should focus on decreasing elk herd densities and group sizes and on understanding the behavioural and environmental drivers that result in co-mingling that makes transmission possible.