Necrotic pharyngitis associated with Mycoplasma bovis infections in American bison (Bison bison)

Mycoplasma bovis has emerged as a significant and costly infectious disease problem in bison, generally presenting as severe, caseonecrotic pneumonia. Three diagnostic cases in which M. bovis is associated with necrotic pharyngitis in bison are described in the current study. The bacterium was isolated from lesions of the pharynx or lung of 3 American bison (Bison bison), at 2 different locations in the upper Midwestern United States, with severe, necrotic pharyngeal abscesses. Chronic caseonecrotic inflammation typical of M. bovis infection in bovines was observed microscopically in the pharynxes of affected bison. A mixed population of bacteria was recovered from the pharyngeal lesions, and Trueperella pyogenes, a frequent secondary pathogen in ruminant respiratory disease, was consistently isolated from the affected animals. Distinctive histopathological features of the pharyngeal lesions favor causation by M. bovis, although a role for T. pyogenes in the clinical presentation cannot be excluded. Veterinarians and producers working with bison should be aware that M. bovis may be associated with pharyngitis in bison.