Identification of a Newly Isolated Avian Infectious Bronchitis Coronavirus Variant in China Exhibiting Affinity for the Respiratory Tract

Abstract

Twelve infectious bronchitis virus (IBV) isolates obtained from commercial chickens in China between 2005 and 2006 were characterized by reverse transcriptase-polymerase chain reaction (RT-PCR) and the sequencing of the entire S1 gene. CK/CH/LSD/05I--an IBV variant, which was unlike the nephropathogenic IBV isolates found in China--exhibited an affinity for the respiratory tract. The variant was identified by phylogenic analysis and basic local alignment search tool (BLAST) searches of the entire S1 gene and by the vaccination-challenge test that was performed using heterologous strains. Further, it was demonstrated that the commercially used H120 vaccine did not provide sufficient protection against this variant; however, the attenuated heterologous IBV tl/CH/LDT3/03 P120, whose parent virus was isolated in China, showed a better efficacy of protection against CK/CH/LSD/05I. This study thus may demonstrate that the use of a combination of commercially available vaccines or of attenuated heterologous strains would provide satisfactory protection against the variant CK/CH/LSD/05I. In addition, the study also revealed that IBV strains exhibiting different pathogenicities were found cocirculating in the chicken flock in China.