Molecular epidemiology of infectious bronchitis virus isolates from China and Southeast Asia

In order to trace the origin and evolution of avian infectious bronchitis v irus (IBV) isolates in China and Southeast Asia, genomic sequencing was use d for molecular characterization of 24 IBV isolates and two reference strai ns in comparison with the published sequences. The 5' region of the S1 gene s, containing hypervariable regions I and II, and 3' region of the nucleoca psid genes, containing cytotoxic T lymphocyte epitopes, were used to constr uct phylogenetic trees for analysis. The results showed that the 24 isolate s could be divided into three distinct groups, that is, American, Asian, an d European. Some isolates formed a distinct Asian phylogenetic group, sugge sting that IBV has existed for some time in Asia. Our results also showed t hat in vivo recombination of IBV may have occurred at a rather high frequen cy, contributing to the diversity of these IBV isolates. Importantly, recom bination events have probably occurred between vaccine strains and field st rains in the natural condition.