Development of safe, effective, and field-applicable Mycoplasma synoviae vaccines for poultry farms: A formidable challenge

Mycoplasma synoviae is a primary pathogenic bacterium threatening global poultry production, which triggers multiple typical clinical manifestations including airsacculitis, upper respiratory inflammation, infectious arthritis and eggshell apex abnormalities (EAA), thereby causing tremendous economic losses to the worldwide poultry industry. Vaccination represents the most reliable and sustainable intervention strategy to prevent M. synoviae outbreaks and mitigate pathogen-induced production losses. At present, commercially available M. synoviae vaccines are divided into two main categories: live-attenuated vaccines and inactivated whole-cell vaccines. Nevertheless, all licensed commercial vaccines possess prominent practical limitations, and the complete pathogenic mechanism of M. synoviae remains to be elucidated. Cumulative experimental evidence has identified multiple M. synoviae protein antigens can mediate host immune protection, which are regarded as promising candidates for novel vaccine design. This review systematically summarizes the latest research advances of M. synoviae vaccines, covering the developmental background, immune characteristics and practical drawbacks of live-attenuated vaccines, conventional inactivated vaccines, and diverse genetically engineered vaccine platforms. This comprehensive overview provides theoretical references and developmental directions for the innovation and optimized field application of next-generation anti- M. synoviae vaccines.