Sequence and phylogenetic analysis of the haemagglutinin genes of H9N2 avian influenza viruses isolated from commercial chickens in Iran.

To determine the genetic relationship of Iranian viruses, the haemagglutinin (HA) genes from ten isolates of H9N2 viruses isolated from commercial chickens in Iran during 1998-2002 were amplified and sequenced. Sequence analysis and phylogenetic studies were conducted by comparing each isolate with those of the available H9N2 strains at GenBank. All these ten isolates had the same sequence -R-S-S-R/G-L- of proteolytic cleavage site of the HA. Nucleotide sequence comparisons of HA gene from Iranian isolates showed 95.2-99.1% identity within the group. Five isolates had leucine (L) at position 226 instead of glutamine (Q). Phylogenetic analysis showed that all our isolates belonged to the G1-like sublineage. Also these isolates showed some degree of homology with other H9N2 isolates e.g., 94.3-96.9% with qu/HK/G1/97, 96.1-98.6% with pa/Chiba/1/97, 95.6-98.2% with pa/Narita/92A/98, and 94.0-96.3% with HK/1073/99. On the basis of phylogenetic and molecular characterization evidence, we concluded that the H9N2 subtype influenza viruses circulating in chicken flocks in Iran since 1998-2002 had a common origin. The results of this study indicated that all Iranian viruses have the potential to emerge as highly pathogenic influenza virus, and considering the homology of these isolates with human H9N2 strains, it seems that the potential of these avian influenza isolates to infect human should not be overlooked.