Relative virulence in bison and cattle of bison-associated genotypes of mycoplasma bovis

Authors: Register, Karen; Olsen, Steven; Sacco, Randy; Ridpath, Julia; Falkenberg, Shollie; Briggs, Robert; KANIPE, CARLY - US Department Of Agriculture (USDA); Cox, Rebecca

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2018
Publication Date: 7/5/2018
Citation: Register, K.B., Olsen, S.C., Sacco, R.E., Ridpath, J., Falkenberg, S., Briggs, R., Kanipe, C., Madison, R. 2018. Relative virulence in bison and cattle of bison-associated genotypes of Mycoplasma bovis. Veterinary Microbiology. 222:55-63. https://doi.org/10.1016/j.vetmic.2018.06.020.
DOI: https://doi.org/10.1016/j.vetmic.2018.06.020

Interpretive Summary: Mycoplasma bovis, a frequent contributor to respiratory disease in cattle, has recently emerged as a major health problem in North American bison. Strong circumstantial evidence suggests it can be the sole cause of disease manifestations in outbreaks of mortality in bison, but direct evidence is lacking. The primary goal of this study was to compare clinical signs and lesions of bison and cattle experimentally exposed to disease-associated isolates of M. bovis recovered from bison. Seven bison and six cattle, all negative for antibodies against M. bovis, were intranasally infected with bison isolates of M. bovis and necropsied 4-6 weeks later. The only clinical sign observed in bison was an elevation in body temperature during the first few weeks after exposure. No clinical signs were apparent in cattle. Tissue damage visible to the naked eye was noted in the lungs of five bison and M. bovis was cultured from each of those lungs. No damage was present in the lungs of infected cattle and M. bovis was not found in any of those samples. Microscopic examination of bison lung tissue revealed moderate to severe lesions and abnormalities consistent with pneumonia. This study is the first to provide direct evidence that M. bovis alone can cause disease in bison, although the isolates used were unable to cause disease in healthy cattle.

Technical Abstract: Mycoplasma bovis, a frequent contributor to polymicrobial respiratory disease in cattle, has recently emerged as a major health problem in North American bison. Strong circumstantial evidence suggests it can be the sole pathogen causing disease manifestations in outbreaks of mortality in bison, but direct evidence is lacking. The primary goal of this study was to compare clinical signs and lesions of bison and cattle experimentally exposed to field isolates of M. bovis recovered from bison. Bison (n=7) and cattle (n=6), seronegative for anti-M. bovis IgG, were exposed intranasally to M. bovis and necropsied 4-6 weeks later. Blood and nasal swabs were collected on day 0 (prior to exposure), day 11 and at necropsy. Samples of lung, lymph node, liver and spleen were also collected at necropsy. The only clinical sign observed was an elevation in the core body temperature of bison during the first few weeks post-exposure. Grossly visible lesions were apparent at necropsy in the lungs of five bison and the lymph node of one bison, while none were evident in cattle. Histologic evaluation revealed moderate to severe pulmonary lesions in four bison. M. bovis was recovered from tissues demonstrating gross lesions and from the lymph nodes of one additional bison and two cattle. All animals seroconverted by the time of necropsy. These data provide the first direct evidence that M. bovis alone is capable of causing respiratory disease in healthy bison, although the isolates used were unable to cause disease in healthy cattle.