Mycoplasma bovis outbreaks in United States bison (Bison bison) herds: A case-control survey

Mycoplasma bovis (M. bovis) is an emerging pathogen in American Bison (Bison bison) inflicting significant morbidity and mortality amongst herds, severe economic impacts to bison producers, and threatening the overall conservation and restoration of this species. This study serves as the first in-depth analysis of disease dynamics and potential risk factors for M. bovis in United States (US) bison herds. US bison producers (n = 81) were surveyed regarding herd demographics, size, biosecurity practices, health management strategies, exposure to potential risk factors (other livestock/wildlife species, shared equipment, climate, etc.) and clinical presentation using a 1:3 case-control study design. Of the 21 case herds, 57 % (12/21) reported having experienced more than one outbreak, an indication to the pervasive, long-lasting effects of this pathogen. Direct herd-level mortality rates were highly variable but significant loss was noted with up to 32 % mortality recorded. Risk factors were evaluated using a generalized linear mixed-effects model with a stepwise additive approach. Herd size (p-value: 0.005, OR: 1.02) and shared fence line with cattle (p-value: 0.009, OR: 5.12) were associated with M. bovis disease. These findings suggest the risk of transmission and subsequent outbreaks are closely linked with the intensification of bison production and proximity to cattle. Health management and disease control strategies for bison can be adapted using our findings to mitigate this emerging pathogen.