Background and Aims: Infectious bronchitis virus (IBV) causes an acute, highly contagious respiratory and kidney disease of chickens which results in significant economic losses in commercial broilers, layers and breeders. Rapid identification of IBV serotypes involved in respiratory complex is a problem in the differential diagnosis.

Background and Aims: Hemagglutinin (HA) protein of Avian Influenza (AI) plays an essential role in the virus pathogenicity. AI H9N2 subtype causes significant economic loss in broiler and layer in poultry farms in Iran. AI viruses have a great involvement in evolutionary changes at nucleotide and amino acid levels and vaccines could induce faster rates of such changes. Up-dated understanding of the genetic changes of AI viruses circulating in Iran is necessary for controlling AI. Materials and Methods: Sequence analysis and phylogenetic study of the HA gene of three H9N2 subtype of AI isolates in Iran in 2010-2011 were studied. Results: Cleavage site of the Iranian 2010-2011 isolates possessed a different motif. Amino acid residue at position 226 at receptor binding site in these isolates was Leucine, which was similar to human viruses. The epitopes for HA showed a great variation related to the year of isolation. According to phylogenetic analysis, Iranian isolates were divided into two main subgroups. But, viruses isolated in this study formed a third minor subgroup. Degree of homology between the 2010-2011 isolates and former Iranian isolates was significantly low. Conclusion:The results revealed that HA of new Iranian AI H9N2 isolates have undergone extensive genetic changes. Definitely, continuous monitoring of genetic changes is a useful tool for updating control strategy for AI outbreak in Iran.