Comparative Genetic Features of S1 Gene from Six Massachusetts and Variant Avian 2 Infectious Bronchitis Viruses Isolated in Iran.

Infectious bronchitis (IB) disease, avian Infectious Bronchitis disease in one of the major cause of respiratory problems and economic loss in poultry industry, even in developed countries with good biosecurity practice. Since the first isolation of the virus in 1931, a lot of serotypes and genotypes of the virus have been reported around the world. The GI-1 lineage, including Massachusetts (Mass) serotype viruses, is one of the most widely spread types worldwide. Moreover, the GI-23 lineage with a growing incidence rate was reported approximately 20 years ago in the Middle East, with no or little homologues vaccine use. The genotype was previously restricted to the Middle East; now, there is evidence that it has spread to European countries, raising concerns regarding potential outbreaks. In the present study, our attempt was to phylogenetically analyze the S1 gene of six isolates from Massachusetts and variant 2 genotypes, which were isolated from broiler and broiler breeder flocks in Iran. The variant 2 viruses were compared to other reported variant 2 viruses from neighboring countries and they had more than 98% identity with the latest reported Iranian variant 2. In addition, Three Mass type viruses were similar to vaccine strains which may be shows continuous circulation of vaccine viruses in the field. This event can cause increasing the risk of their mutation or even reversion to virulence after several passages in natural host, furthermore circulating viruses may recombinant with virulent field viruses and cause emergence of new variants. Considering the variable nature of IB viruses in which few changes lead to important differences, continuous epidemiological surveillance along with clinical studies of new isolates, are crucial to a better understanding of their pathogenicity and subsequent disease control.