Systemic mycoplasmosis with dystocia and abortion in a North American bison (Bison bison) herd

The current study describes a fatal Mycoplasma bovis infection in a North American bison (Bison bison) cow and her aborted fetus in a herd suffering unusual mortality associated with dystocia and abortion. Postmortem evaluation of the subject case found severe caseonecrotic bronchopneumonia, chronic fibrinous pleuritis and pulmonary sequestra, foci of caseous necrosis in the kidneys, and necrotizing endometritis and placentitis. Histologic findings in the maternal tissues include endometrial and placental necrotizing vasculitis and changes in the lung similar to those previously described for M. bovis-associated pneumonia in feedlot bison. Gross and microscopic lesions were not observed in the fetus. Maternal lung, uterus, kidney, and placenta as well as fetal lung and kidney were positive for M. bovis by polymerase chain reaction (PCR) as were the Mycoplasma-like colonies cultured from these tissues. The presence of M. bovis in maternal and fetal tissues was further demonstrated using nucleic acid extracts in a pan-Mycoplasma SYBR Green PCR assay targeting the 16S-23S ribosomal RNA spacer region with post-PCR dissociation curve analysis and sequencing of the resulting amplicons. Immunohistochemistry (IHC) testing on maternal lung and uterine caruncle was strongly positive for M. bovis antigen. A variety of methods, including culture, PCR, and IHC, failed to identify other bacterial or viral pathogens in any of the tissues evaluated. These data are the first to implicate M. bovis as a cause of placentitis and abortion in bison.