Evaluating the MS-HLJ strain as a novel inactivated vaccine candidate: Long-term immune protection against Mycoplasma synoviae in poultry.

Mycoplasma synoviae (MS) is highly prevalent in chicken flocks and causes significant economic losses in the poultry industry. Vaccination is an effective measure for preventing and controlling MS infection in chickens, making it crucial to isolate, identify, and analyze the immunogenicity of MS to develop vaccines against mycoplasmosis in poultry. In this study, the MS-HLJ strain was isolated from the joint tissue fluid of a suspected case of MS infection in chickens, and its pathogenicity in specific-pathogen-free chickens was investigated. The immunogenicity of MS-HLJ was further assessed by preparing and administering an oil-emulsion inactivated vaccine to 14-d-old specific-pathogen-free chickens. The vaccinated groups showed significantly higher serum hemagglutination inhibition antibody levels 21 d post-vaccination than those of the control group. Fourteen days after challenge, the incidence was 80 % and 20 % in the control group and immunized chickens, respectively. Moreover, 150 d after immunization, the serum hemagglutination inhibition antibody titer (5 log) remained above the required protection standard threshold. Our data indicate that the MS-HLJ inactivated vaccine is a promising candidate for protection against MS infection in poultry.