Development and immunogenicity of a novel subunit vaccine candidate against avian metapneumovirus

aMPV subtype B remains one of the major respiratory pathogens affecting commercial poultry worldwide despite the widespread implementation of vaccination programs. In the present study, epidemiological surveillance, virus isolation, and immunogenic evaluation of a newly developed subunit vaccine against aMPV subtype B were conducted.

Clinical samples, representing 115 chicken flocks from 16 commercial poultry farms located in three regions of Kazakhstan, were screened for aMPV subtype B using multiplex real-time RT-PCR. Approximately 20% of the samples collected during the spring season tested positive for aMPV, with subtype B predominating among the detected strains. Phylogenetic analysis revealed that the identified viruses clustered within subtype B and were closely related to vaccine-like strains while forming a distinct monophyletic group.For virus isolation, field samples that tested negative for IBV, NDV, ILTV, and Mycoplasma gallisepticum were propagated in Vero cells. Cytopathic effects were observed after 3-4 passages, and one isolate, designated Ck/B/Kaz/256/25, was successfully recovered from a laying hen. The isolate was subsequently confirmed by electron microscopy, gel electrophoresis, and was used for the development of a subunit vaccine.

The immunogenicity of the vaccine was evaluated in chickens following a prime-boost immunization regimen and compared with that of a commercial live vaccine. The subunit vaccine induced 100% seroconversion by day 14 post-vaccination and elicited significantly higher IgG and virus-neutralizing antibody titers than the live vaccine. Neutralizing antibody titers were 8-fold higher after primary immunization and 16-fold higher after booster immunization compared with those in the live vaccine group. Furthermore, the subunit vaccine significantly enhanced the expression of IFN-γ and IL-4, indicating activation of both Th1- and Th2-mediated immune responses.

Overall, these findings demonstrate that the developed subunit vaccine induces robust and durable humoral and cellular immune responses and represents a promising candidate for the prevention and control of aMPV subtype B infection in poultry.