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

Abstract

Objectives 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. Methods 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. Results 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. Conclusion 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.