The high mutation rates of infectious bronchitis virus (IBV) pose economic threats to the poultry industry. In order to track the genetic evolutionary of IBV isolates circulating in yellow chickens, we continued to conduct the genetic analyses of the structural genes S1, E, M, and N from 64 IBV isolates in southern China during 2009–2017. The results showed that the dominant genotypes based on the four genes had changed when compared with those during 1985–2008. Based on the S1 gene phylogenetic tree, LX4-type (GI-19) was the most dominant genotype, which was different from that during 1985–2008. The second most dominant genotype was LDT3-A-type, but this genotype disappeared after 2012. New-type 1 (GVI-1) isolates showed increasing tendency and there were four aa (QKEP) located in the hypervariable region (HVR) III and one aa (S) insertion in all the New-type 1 isolates. Both the analyses of amino acid entropy and molecular evolutionary rate revealed that the variations from large to small were S1, E, M, and N. Purifying selection was detected in the S1, E, M, and N gene proteins, which was different from the positive selection during 1985–2008. Six isolates were confirmed to be recombinants, possibly generated from a vaccine virus of the 4/91-type or LDT3-A-type and a circulating virus. The estimated times for the most recent common ancestors based on the S1, E, M, and N genes were the years of 1744, 1893, 1940, and 1945, respectively. Bayesian skyline analysis revealed a sharp decrease in genetic diversity of all the four structural genes after 2010 and since late 2015, the viral population rapidly rose. In conclusion, the IBVs circulating in southern China over the past decade have experienced a remarkable change in genetic diversity, dominant genotypes, and selection pressure, indicating the importance of permanent monitoring of circulating strains and the urgency for developing new vaccines to counteract the emerging LX4-type and New-type IBVs.

To enhance the efficacy of Newcastle disease virus (NDV)-vectored bivalent vaccines against novel variant infectious bursal disease virus (nVarIBDV), we engineered recombinant NDV strains expressing nVarIBDV VP2 proteins fused with the viral nucleocapsid NC motif, thereby leveraging the NDV assembly pathway. The resulting vaccine candidates, rDM-VP2NC and rDM-VP2mNC, exhibited markedly enhanced VP2 expression in vitro. Furthermore, the NC motif promoted VP2 co‑localization with the NDV M protein near the cell membrane and facilitated its efficient incorporation into budding virus-like particles (VLPs) and virions. In chickens challenged with a nVarIBDV strain, immunization with rDM‑VP2NC or rDM‑VP2mNC provided superior protection compared to the parental rDM‑VP2 strain, as demonstrated by a drastic reduction in bursal viral load and the absence of detectable pathological lesions. These results establish the NC motif as a key determinant for enhancing antigen assembly and immunogenicity in NDV vectors. Collectively, this work presents a novel strategy for engineering NDV as a vector that directly packages protein cargo within virions, with broad implications for vaccine and oncolytic virotherapy development.