Demonstration of Mycoplasma bovis by immunohistochemistry and in situ hybridization in an aborted bovine fetus and neonatal calf.

Mycoplasmas are host-specific commensals on mucous membranes of the genital tract, but infection and clinical disease by Mycoplasma bovis in the genital tract of cattle is not well described. In the current study, 1 aborted bovine fetus and 1 neonatal calf were examined macroscopically and histologically. For the detection of M. bovis, bacterial isolation, immunohistochemistry (IHC), and in situ hybridization (ISH) were performed. For further characterization of the inflammatory infiltrates, IHC was performed using antibodies to cluster of differentiation (CD)3, CD79a, lysozyme, L1, S-100A8, S-100A9, and von Willebrand factor VIII. Gross examination revealed a lobular consolidation of the lung. Histologically, the lungs of both animals showed an interstitial pneumonia associated with suppurative bronchopneumonia, intraalveolar multinucleated giant cells, and lymphocytic aggregates. The expression of L1, S-100A8, and S-100A9 in multinucleated giant cells supports a histiocytic origin. Mycoplasma bovis antigen was detected by IHC in brain, lung, liver, and placenta of the fetus, and M. bovis DNA was detected by ISH in various organs of the fetus, including lung and placenta and within the lung of the calf.