Protection of chickens against M. synoviae infection by vaccination with a recombinant fowl adenovirus 4-P50.

Abstract

Mycoplasma synoviae (M. synoviae, M.S.) is a causative agent responsible for airsacculitis, respiratory tract infections, arthritis, and eggshell apex abnormalities (EAA) in poultry, causing severe economic losses to poultry industry worldwide. Effective vaccines against MS infection are urgently needed. FAdV-4 has been prevalent in China since 2015 and offers an advantage as a viral vector for the development of recombinant live vaccines. In this study, the recombinant adenovirus vector pKHPFAdV-4-ON1-p50 was constructed by inserting a M. synoviae p50 gene expression cassette into the 1966 bp gene deletion site of the attenuated adenovirus vector pKHPFAdV-4-ON1. The recombinant virus rFAdV-4-ON1-P50 was then rescued and used to inoculate chickens. Our data show that inoculation of chickens with rFAdV-4-ON1-P50 induced dose-dependent humoral immune responses. High-dose immunization activated Th1-type cellular immune responses. Safety evaluations revealed no significant differences in gross pathology or histopathology (H&E staining) between vaccinated and control groups. Challenge experiments showed that the M. synoviae recombinant adenovirus type-4 vectored vaccine significantly alleviated M. synoviae-induced weight loss (P&#x202f;<&#x202f;0.01), inhibited pathogen replication in vivo (P&#x202f;<&#x202f;0.01), and reduced lesions in the joints and footpads, indicating effective immune protection. These results indicate that inoculation with rFAdV-4-ON1-P50 provided chickens with protection against M. synoviae infection, suggesting that recombinant virus rFAdV-4-ON1-P50 might be used as a potential vaccine candidate for the prevention and control of M. synoviae infection and providing new insights into the development of novel adenovirus-vector based vaccines for other avian diseases.