Objective  To understand the evolutionary relationship and pathogenicity of Mycoplasma synoviae (MS) clinical infection strains in Fujian Province.

  Method  MS detection and isolation were performed from cleft palate and tracheal swab samples of chickens suspected of MS infection to obtain MS clinical isolates, and the vlhA gene phylogenetics of MS isolates were carried out. And also, the pathogenicity and horizontal transmission ability of MS isolates from Fujian province were evaluated using 7-day-old SPF chickens infected by eye and nasal route, including clinical symptoms and anatomical pathology, histopathology of trachea, MS re-isolation of trachea and MS antibody.

  Result  The positive rate of MS in tracheal swabs was significantly higher than that in cleft palate swabs. A total of 9 MS isolates showed that there was diversity in the vlhA gene, and different isolates had different evolutionary sources. According to the phylogenetics of vlhA gene, 6 MS isolates were selected to infect 7-day-old SPF chickens, no obvious clinical symptoms were caused in SPF chickens from 1 to 21 days after infection. It was found that one chicken had mild air sacculitis in HI strain group at 14 and 21 days after infection and in SD6 strain group at 21 days after infection via necropsy, and other chickens including cohabitation chickens did not have obvious clinical anatomical and pathological changes. Histopathological analysis showed that there were significant differences in the tracheal lesion to different MS isolates after 7, 14, and 21 days of infection. The results showed that re-isolations of MS from trachea were with significant differences to different MS isolates, and SD19 and SD6 strains had strong horizontal transmission ability. MS antibody detection found that only 1 infected chicken and 1 cohabiting control chicken in the SD19 infection group turned positive for antibodies at 21 days after infection.

  Conclusion  Tracheal samples were more suitable for the detection and isolation of MS. MS isolates were rather difficult causing clinicopathological changes in 7-day old SPF chickens, and also MS isolates could present and colonize in the trachea to cause histopathological lesion, and there were significant differences within different isolates. Therefore, the results laid the foundation for subsequent research on the prevention and control of Mycoplasma synoviae infection.