Nucleotide Sequence Analysis of S۱ Gene among Iranian Avian Infectious Bronchitis Viruses Isolated during ۲۰۰۱-۲۰۰۲

Infectious bronchitis (IB) virus genome codes for four structural proteins, among which the S۱ subunit of spike glycoprotein comprises the major epitopes to induce neutralizing antibodies. This study involved the comparison of the full S۱ sequences of five IB viruses, namely two Massachusetts and three ۷۹۳/B serotypes, isolated from IB outbreaks during ۲۰۰۱-۲۰۰۲, with all other Iranian and foreign ۷۹۳/B isolates and ۱۰ known serotypes. Analysis of S۱ subunit showed three unique amino acid changes at positions ۳۴۹ (V to L), ۳۹۲ (T to N), and ۳۹۳ (Q or R to T or K or S) for the Iranian ۷۹۳/B isolates, compared to those of the foreign ۷۹۳/B isolates reported before ۲۰۰۶ (onset of vaccination with ۷۹۳/B vaccine in Iran). They were used as amino acid markers for the differentiation of Iranian ۷۹۳/B isolates for years. Sequence alignment of the Iranian isolates with those of the foreign ones reported after ۲۰۰۶ demonstrated that amino acids ۳۹۲ and ۳۹۳ were no longer considered as amino acid markers, and only the change in amino acid ۳۴۹ still remained specific to the Iranian ۷۹۳/B isolates. Phylogenetic tree sequence analysis revealed that the Iranian ۷۹۳/B isolates were closely related indicating that they came from a single source, more probably from France. There was a very close correlation between the first detection of ۷۹۳/B serotype and the time of French chicken meat importation. Moreover, it was shown that one of the Massachusetts isolates was completely identical with the H۱۲۰ vaccine strain. Furthermore, the other Massachusetts isolate with two amino acid changes at positions ۶۴ (G to E) and ۹۵ (S to R) was very similar to this vaccine strain. It seems that the latter isolate is a passaged chicken H۱۲۰ vaccine strain.

کلیدواژه ها:

Infectious bronchitis virus ، ۷۹۳/B serotype ، S۱ gene ، Amino acid marker ، Phylogenetic analysis