A new recombinant avian metapneumovirus vaccine candidate provides complete protection against the novel variant infectious bursal disease virus in chickens

Abstract

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive condition in chickens, caused by the infectious bursal disease virus (IBDV). The recent emergence of novel variant IBDV (nVarIBDV) poses a significant threat to the global poultry industry. However, currently available vaccines provide only limited protection against nVarIBDV strains. In this study, a recombinant avian metapneumovirus subtype B (aMPV/B) expressing the nVarIBDV VP2 gene (rLN16A-nVarVP2) was successfully rescued by inserting the gene between the G and L genes of the attenuated aMPV/B strain LN16-A. Immunofluorescence and Western blotting analyses confirmed stable VP2 expression in vitro. Further evaluation showed that VP2 insertion did not alter the growth kinetics of the parental virus, and the expression remained stable after 20 serial passages. A single immunization with rLN16A-nVarVP2 elicited robust humoral and cellular immune responses in specific pathogen-free chickens, inducing high levels of neutralizing antibodies against both nVarIBDV and aMPV/B, as well as Th1 (IL-2, IFN-γ) and Th2 (IL-4, IL-6) cytokines. Moreover, rLN16A-nVarVP2 conferred complete (100%) protective efficacy against both nVarIBDV and aMPV/B, fully prevented bursal atrophy and clinical signs associated with aMPV/B infection, and markedly decreased bursa viral load (nVarIBDV) and turbinate viral shedding (aMPV/B). Our findings suggest that rLN16A-nVarVP2 represents a promising live attenuated bivalent vaccine candidate for preventing infections caused by nVarIBDV and aMPV/B.