A New Threat Emerges: The First Detection of GVIII Genotype IBV in China and the Urgent Need for Molecular Surveillance.

In 2025, an infectious bronchitis virus (IBV) strain of the GVIII genotype was identified and isolated from a poultry farm in Hebei Province, China, representing the first documented detection of this IBV genotype within the country to date. Nucleotide homology analysis revealed that the S1 gene of this isolate shares 62.2%-96.9% sequence identity with previously reported GVIII-type strains from other countries. Comprehensive phylogenetic analysis of the complete genome indicated that this strain originated from a single recombination event: Its S gene may have been derived from the GVIII-1 lineage strain IBV/Ck/USA/CA/21-1883, while the remaining genomic regions were likely acquired from the GI-19 lineage strain SD. Pathogenicity evaluation demonstrated that infected flocks exhibited reduced body weight gain, with 40% of chickens showing signs of diarrhea. Necropsy findings included hemorrhagic lesions at the proventriculus-gizzard junction and within the bursa of Fabricius. Moreover, 85% of infected hens developed severe oviduct hypoplasia, and 90% showed a reduction in follicular number. The isolate described in this study constitutes the first detection of a GVIII genotype IBV strain in China, although its route of introduction remains undetermined. The emergence of this strain highlights the necessity for sustained molecular surveillance of IBV and the development of genotype-matched vaccines.