The molecular, antigenic, and pathogenic characterization of novel IBV of GI-22 lineage endemic in China

Recently, chicken infectious bronchitis (IB), caused by the infectious bronchitis virus (IBV), has emerged as one of the top diseases in the poultry industry in China. Site mutations and recombination events contribute to the high genetic diversity of IBV. In this study we considered the S1 sequences of 30 GI-22 lineage strains, including 24 isolates previously identified, isolated from flocks with the clinical signs of nephritis, egg production drop or oviduct lesions, which shared common clinical signs with the classical GI-22 lineage IBV. The S1 amino acid sequences of all 30 isolates were highly diverse from those of classical GI-22 viruses and these 30 isolates could be grouped into five clusters with high diversity of S1 protein with each other, the S1 amino acid sequence homology ranging from 83.48% to 100%. Cross-neutralization assays revealed that these 30 novel GI-22 lineage isolates exhibited at least three serotypes. Furthermore, infection studies showed that these novel IBV isolates could cause lesions of glandular stomach, kidney and reproductive system in chickens, and showed potential efficient transmission ability with high mortality. Analysis of the receptor binding domain (RBD) revealed that these novel IBV strains of GI-22 lineage also carried 14-amino-acid insertion in HVR1, which was distinctly different from the current vaccine strains. Overall, our data provided insights into the emergence and highly variant antigenicity of novel GI-22 lineage IBVs, highlighting the need for development of IB vaccines against novel and pathogenic GI-22 lineage IBVs.