[Evaluation of antigenic relationship of Guangxi isolates of infectious bronchitis virus]

Monovalent antisera of 3 vaccine strains and 7 representative field isolates were prepared based on the comparison of genetic diversity of the hypervariable region I of S1 gene (HVR I from 3 infectious bronchitis (IB) vaccine strains (H120, Ma5 and 4/91) ,one reference strain M41 and 26 IB field isolates. These 30 strains were classified in 7 different genotypes, respectively. Virus-neutralizing test on tracheal organ cultures (TOC) with chicken embryo were used to evaluate relatedness values of the antigenicity based on the antibody titer, to analyze the antigenic relationships between the isolates and vaccine strains, as well as to determine the serotypes of 26 IB viruses isolated from the field in Guangxi between 1985 and 2008. The results showed 30 strains were classified into 7 distinct serotypes and there were two predominant serotypes within the 26 isolates, serotypes 1 (totally 13 isolates) and serotype 2 (totally 5 isolates), respectively. In addition, there were some differences observed between the results of serotyping and the genotyping (including the S1, N, M and 3'UTR). The results of the study demonstrated that there were different predominant serotypes and multiple serotypes of IBV circulated in Guangxi in recent years, antigenic variation existed between Guangxi field isolates and vaccine strains.