Full-length characterization and phylogenetic analysis of hemagglutinin gene of H9N2 virus isolated from broilers in Iran during 1998-2007.

H9N2 avian influenza A viruses (AIV) have become panzootic in Eurasia over the last decade and are endemic in Iran since 1998, and inactivated vaccine has been used in chickens to control the disease. The hemagglutinin (HA), one of eight protein-coding genes, plays an important role during the early stage of infection. To study their evolution and zoonotic potential, we conducted an in silico analysis of H9N2 viruses that have infected broiler in Tehran Province, Iran between 1998 and 2007. The complete coding region of HA genes from nine H9N2 subtypes isolated from chicken flocks in Tehran Province during 1998-2007 was amplified and sequenced. Sequence analysis and phylogenetic studies of H9N2 subtype viruses on the basis of data of 9 viruses in this study and 30 selected strains are available in the GenBank. Sequence and phylogenetic analyses revealed a large number of similar substitution mutations and close evolutionary relation among sequences of HA. The isolates possessed two types of amino acid motif -R-S-S-R/G-L- and -R-S-N-R/G-L- at the cleavage site of HA. The results showed that all nine representative H9N2 isolates belong to low pathogenic AIVs since none of the amino acid sequences at the cleavage site of the HA of the isolates possessed the basic motif required for highly pathogenic viruses (R-X-R/K-R). Six out of these nine isolates possessed leucine at position 226, which prevails in the sequences found in human strains. 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., 89.46-93.93.39% with qu/HK/G1/97 and 93.39-98.39% with pa/Narita/92A/98. The available evidence indicates that HA genes of H9 influenza virus circulating in Iran during the past years were not well conserved. Our finding emphasizes the importance of reinforcing AIV surveillance, especially after the emergence of high pathogenicity in poultry in Iran.