Development of a recombinant chimeric Newcastle disease virus-vectored vaccine conferring single-dose, triple protection against genotype VII NDV, IBDV, and H9N2 AIV

Newcastle disease, infectious bursal disease, and H9N2 avian influenza critically threaten the poultry industry worldwide. To achieve single-dose protection against all three pathogens, a recombinant chimeric Newcastle disease virus (NDV) vector vaccine was developed using a genotype-matched strategy. The fusion and hemagglutinin-neuraminidase genes of the LaSota vaccine strain were replaced with those from a prevalent genotype VII virulent NDV strain. The hemagglutinin gene of H9N2 avian influenza virus (AIV) and the VP2 gene of a very virulent infectious bursal disease virus (IBDV) strain were inserted between the P/M and F/HN gene junctions, respectively. The resulting virus, rLaS-VIIF/HN-HA-VP2, exhibited low pathogenicity (intracerebral pathogenicity index = 0.20; mean death time > 168 h) and replication kinetics similar to the parental strain. A single ocular/nasal dose in specific-pathogen-free chickens elicited strong antibody responses: ELISA titers >3000 against IBDV, hemagglutination inhibition titers of 4.8 log₂ against H9N2 AIV, and significant titers against genotype VII NDV. Challenge experiments at 21 days post-immunization showed complete protection against lethal infection with very virulent IBDV, H9N2 AIV, and genotype VII NDV. Vaccinated chickens displayed no mortality or clinical signs, reduced viral shedding, and minimal tissue damage. These findings demonstrate that rLaS-VIIF/HN-HA-VP2 is a safe and effective single-dose trivalent vaccine candidate, suitable for integrated control of three major avian diseases.