Mycoplasma bovis outbreak and maintenance of subclinical infections in an exposed cohort of juvenile American bison (Bison bison)

Authors: BUTTKE, DANIELLE - Us National Park Service; SCHWARTZ, KATIE - University Of Wyoming; SCHWALBE, ERIN - University Of Wyoming; KILLION, HALCYON - Wyoming State Veterinary Laboratory; SONDGEROTH, KERRY - University Of Wyoming; Kaplan, Bryan; MALMBERG, JENNIFER - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2025
Publication Date: 7/11/2025
Citation: Buttke, D.E., Schwartz, K., Schwalbe, E., Killion, H., Sondgeroth, K., Kaplan, B.S., Malmberg, J. 2025. Mycoplasma bovis outbreak and maintenance of subclinical infections in an exposed cohort of juvenile American bison (Bison bison). Journal of Wildlife Diseases. 61(3):563-573. https://doi.org/10.7589/JWD-D-24-00117.
DOI: https://doi.org/10.7589/JWD-D-24-00117

Interpretive Summary: The American bison is an economically and culturally important species that is exceptionally susceptible to respiratory disease caused by the bacteria Mycoplasma bovis (M. bovis). In bison, M. bovis causes high morbidity and mortality outbreaks though the effects on bison calves has never been formally investigated. In this study, a cohort of bison calves was established following an outbreak of M. bovis in a closed, extensively managed herd. Longitudinal collection of nasal swabs show that calves can be infected with M. bovis in the absence of signs of clinical disease with some calves being chronically infected throughout the 12-month study period. These chronic carriers pose a risk for future M. bovis outbreaks and emphasize the need for effective testing to identify these animals following an outbreak as an effective herd management strategy.

Technical Abstract: The American bison (Bison bison) is an ecologically, economically, and culturally significant species that is exceptionally vulnerable to disease caused by Mycoplasma bovis. In contrast to livestock in which M. bovis is on of many infectious agents comprising the bovine respiratory disease complex, infection in bison is characterized by severe pneumonia and potential for systemic disease in the absence of co-infecting pathogens. In bison, morbidity and mortality are highest in adult cows, whereas calves and yearlings infrequently present with clinical disease. The infection dynamics of M. bovis in young bison exposed during an outbreak have not been fully characterized. Here we describe a severe outbreak of M. bovis in a closed, extensively managed herd from which we established a cohort of young bison for longitudinal observation, sampling, and testing. Our findings indicate that M. bovis can colonize the nasopharynx of calves and yearlings during an outbreak, often without causing apparent clinical signs. While some animals cleared the infection during our 12-month follow-up study, others remained PCR- and culture-positive, highlighting the potential for asymptomatic carriage in bison calves as a source of subsequent outbreaks. Using a paired swabbing approach, we show that sampling the superficial nasal cavity is adequate for detection of M. bovis during an outbreak. Over time, however, deep sampling of the nasopharynx is necessary to maximize detection of subclinical infections. Uncertainty in detection using PCR on nasal swab samples can complicate herd assessments and limit our ability to fully assess risk. This study emphasizes the difficulty of identifying chronic carriers following an outbreak and underscores the need for further research to inform M. bovis management and minimize risk in the sensitive and iconic American bison.