Genomic and pathogenic insights into a new GVI-1 infectious bronchitis virus strain isolated in Northeast China

Infectious bronchitis is a severe disease caused by the infectious bronchitis virus (IBV), resulting in significant economic losses to the poultry industry. We isolated an IBV strain from H120-vaccinated layers in Northeast China called CK/CH/LN/2301. Phylogenetic analysis of the S1 gene classified the isolate within the GVI-1 genotype. Further analysis revealed that CK/CH/LN/2301 is a recombinant strain derived from the GVI-1, GI-19, and 4/91 genotypes, with recombination events primarily located in the open reading frame (ORF) 1a region. Experimental infection of 1-day-old specific pathogen-free (SPF) chickens induced clinical signs, including depression and head shaking, with 10% mortality rate. Necropsy revealed characteristic tracheal hemorrhages, and quantitative viral load analysis demonstrated significantly higher viral titers in tracheal tissues than in other organs. Histopathological examination confirmed lesions in the trachea, lungs, kidneys, and duodenum. The neutralization assay showed that CK/CH/LN/2301 exhibited limited cross-neutralization with existing vaccine strains such as H120. Predicted structural comparison of the S protein revealed substantial conformational differences in the hypervariable regions (HVRs) and the S1 subunit between CK/CH/LN/2301 and the vaccine strains, which may contribute to the reduced level of cross-protection provided by current vaccines. Our findings demonstrate that GVI-1 IBV strains are undergoing evolution, highlighting the urgent need for updated vaccine strategies to control emerging variants.