Abstract

Five field isolates of infectious bronchitis virus (IBV) were isolated from chicken flocks in the Hubei province of China. The IBVs were characterized by RT-PCR and phylogenetic analysis. The S1 gene sequence of the spike glycoprotein was compared with previously published gene sequences of IBV strains. Analysis of the nucleotide and deduced amino acid sequences revealed that the five isolated strains shared greater than 79% nucleotide and 73% amino acid homology within the S1 region. The nucleotide similarity of the S1 protein gene between the five Chinese IBV isolates and 15 strains of other IBVs varied from 73 to 97%. The identity of the S1 protein gene between the five Chinese IBV isolates and 15 strains of other IBVs varied from 71 to 98%. Most of the sequence variations were observed between amino acids 51-96, 123-156, 218-314, 361-397, and 427-497. Phylogenetic analysis suggested that the five IBV isolates were divided into two genotypes. Four isolates including JS, JZ, XT, and XG formed a cluster together with other Chinese strains with a 99% nucleotide sequence identity and 97% amino acid sequence identity. These isolates belong to group C of IBVs, which was not related to conventional vaccines strains. This group likely represents strains indigenous to China. By contrast, the HP strain was a member of group B, which showed a close relationship with H120 (95% nucleotide similarity and 98% amino acid sequence identities). In conclusion, this study clearly demonstrates that there are at least four groups of IBVs prevailing in China and variant IBV strains continue to emerge. The disease outbreaks might have been caused by infection of multiple strains of IBV.

Key words: Infectious bronchitis virus; identification; S1 gene; molecular characteristics; sequencing; phylogenetic analysis.