Diagnostic investigation of Mycoplasma hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs.

Mycoplasma hyorhinis (M. hyorhinis) is a commensal of the upper respiratory tract in swine with the typical clinical presentations of arthritis and polyserositis in postweaning pigs. However, it has also been associated with conjunctivitis and otitis media, and recently has been isolated from meningeal swabs and/or cerebrospinal fluid of piglets with neurological signs. The objective of this study is to evaluate the role of M. hyorhinis as a potential pathogen associated with neurological clinical signs and central nervous system lesions in pigs. The presence of M. hyorhinis was evaluated in a clinical outbreak and a six-year retrospective study by qPCR detection, bacteriological culture, in situ hybridization (RNAscope®), and phylogenetic analysis and with immunohistochemistry characterization of the inflammatory response associated with its infection. M. hyorhinis was confirmed by bacteriological culture and within central nervous system lesions by in situ hybridization on animals with neurological signs during the clinical outbreak. The isolates from the brain had close genetic similarities from those previously reported and isolated from eye, lung, or fibrin. Nevertheless, the retrospective study confirmed by qPCR the presence of M. hyorhinis in 9.9% of cases reported with neurological clinical signs and histological lesions of encephalitis or meningoencephalitis of unknown etiology. M. hyorhinis mRNA was confirmed within cerebrum, cerebellum, and choroid plexus lesions by in situ hybridization (RNAscope®) with a positive rate of 72.7%. Here we present strong evidence that M. hyorhinis should be included as a differential etiology in pigs with neurological signs and central nervous system inflammatory lesions.