Abstract
A comprehensive study of the epidemiology and pathogenicity of infectious bronchitis virus (IBV) in China was carried out by molecular characterization of the S1 gene from 46 isolates obtained for this study and 174 reference strains isolated over a 15-year period. Nine types were found according to sequence analysis and phylogenetic study of the S1 gene. The co-circulation of multiple IBV types and the ongoing emergence of IBV variants are the epidemiological challenges in China. Factors contributing to the continual emergence include mutations, insertions and deletions in the S1 protein genes; recombination between local IBV strains circulating in chicken flocks in China; and recombination between local strains and vaccine strains. Vaccination-challenge analysis between circulating field strains and Mass-type H120 vaccine indicated the need to develop new vaccines from local IBV strains. These results also emphasize the importance of continued IBV surveillance in China.