In the present study, the genetic variations were examined of hemagglutinin genes of 4 recent H9N2 subtype avian influenza viruses isolated in the Tehran province of Iran. These hemagglutinin genes were amplified and sequenced in order to compare these viruses with the previous isolates from Iran and some other countries from all over the world. The full length hemagglutinin genes of 112 H9N2 avian influenza strains isolated from chickens, and also migratory birds from all over the world, including 68 strains isolated in Iran during 1998-2012, were genetically analyzed. The amino acids in the hemagglutinin cleavage site of the all 4 recent isolates possessed a PAKSSR/GL motif, which is a different motif when compared with the predominant PARSSR/GL motif in the hemagglutinin of the Iranian H9N2 strains isolated before 2010. All 4 recent isolates possessed histidine, alanin, leucine and isoleucine at positions 183, 190, 226 and 227 respectively, which are the key residues in receptor-binding sites. Genetic and phylogenetic analysis of the hemagglutinin genes showed that recent H9N2 strains isolated from chickens in Iran during 2010-2012, formed a distinct subgroup of the previous strains. Recent changes in the H9N2 viruses may be the result of the widespread circulation of these viruses in recent years. This may be due to the lack of adequate surveillance and control programs, such as vaccination and quarantine. Hence, it is highly recommended that continuous surveillance programs and genetic analysis of ongoing changes to H9N2 should be considered.
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