Abstract: Mycoplasma hyorhinis is ubiquitous in the pig population and could cause systemic diseases such as polyserositis and polyarthritis. At present, there is no standard challenge model for M. hyorhinis, as well as standard virulent strain. In this study, a M. hyorhinis strain was isolated from the synovial fluid of a pig with typical clinical symptoms. It was identified to be M. hyorhinis by analysis of PCR, colony and bacterial morphology identification and multi locus sequence typing (MLST). To evaluate the pathogenicity of the strain, 1-month-old snatch-farrowed, porcine-colostrum-deprived (SF-pCD) pigs were inoculated with the isolated strain. The infected piglets showed obvious joint swelling and lameness. The daily weight gains of the infected piglets were significantly lower than those of the pigs in the control group. Three of the infected piglets died during the observation period. At necropsy, the infected pigs showed extensive pleurisy, peritonitis, pericarditis and arthritis. The histopathological analysis of the lung tissues showed thickened alveolar septa but no shrimp-like lesions. The challenge strain can be re-isolated from the tonsils, lungs, hearts and joint effusions of the infected pigs. To sum up, a strain of M. hyorhinis was isolated in this study, and the pigs artificially infected which showed typical symptoms. The establishment of the challenge model laid an important foundation for the study of M. hyorhinis pathogenic mechanisms and vaccine development.

Key words: Mycoplasma hyorhinis, isolation and identification, pathogenicity