Phylogenetic analysis of infectious bronchitis coronaviruses newly isolated in China, and pathogenicity and evaluation of protection induced by Massachusetts serotype H120 vaccine against QX-like strains.

Abstract

Seventy-eight isolates of avian infectious bronchitis virus (IBV) were obtained from different field outbreaks in China in 2009 and genotyped with 34 reference strains. Four genotypes of IBV and three new isolates were identified by phylogenetic analysis and BLAST searches of the entire S1 gene. The results showed that most IBV strains that have circulated in China in recent years belong to the genotype of QX-like strains, and that they could be grouped further into two clusters, regardless of the level of genetic variation displayed. A study of pathogenicity that used three QX-like strains--ck/CH/LSD/091003, ck/CH/LDL/091022 and ck/CH/LJL/090330--showed that the isolates caused the most severe lesions in the kidneys and were therefore nephropathogenic strains with various levels of virulence in specific pathogen free chickens. A vaccination-challenge test that was performed using the three QX-like strains showed that the commercially available H120 vaccine did not provide sufficient protection against challenge with the QX-like isolates, as demonstrated by comparison of the clinical signs, pathological lesions and virus recovery from the trachea and kidney of unvaccinated-challenged and vaccinated-challenged birds.