Sequence characterization of full-length S1 gene of infectious bronchitis viruses isolated from poultry farms in Khorasan Razavi, Iran

Abstract

Infectious bronchitis virus (IBV) causes heavy economic losses in chicken farms worldwide. Like many other viral diseases,vaccination is the gold standard approach in controlling and preventing the spread of IBV. However, IBV is continuously evolving andnew strains of this virus emerge that, due to variable antigenic cross-reactivity, may reduce or nullify the protective effect of vaccinationprograms. Therefore, advance knowledge of the IBV strain(s) circulating in a region will be very useful in deciding which commercialvaccine(s) would be most effective. In this line, we analyzed the nucleotide sequence of the full-length S1 gene of IBV viruses isolatedfrom broiler and layer flocks in the northeast of Iran. Three to five birds from each of 19 suspected flocks were used to collect tissuesamples and six individual virus isolates were obtained from these tissue samples. Homology analyses using S1 gene nucleotide sequencedata revealed that three out of our six isolates were closest to QX-like IBV strains and the rest had the best homology with Variant 2-like(IS/1494) strains. Phylogenetic analyses grouped our isolates into two clusters, one that included Chinese QX isolates and anotherformed of Variant 2-like isolates mainly reported in Middle Eastern countries. Our study shows that QX and Variant 2-like strainsare major IBV viruses circulating in broiler and layer flocks of the northeast of Iran, an important fact that needs to be considered forvaccination programs.