ABSTRACT
The H9N2 subtype of avian influenza viruses [AIVs] have spread in Asia and Middle East countries and have become a serious threat to poultry industry in Iran. Characterization of genes of H9N2 subtype involving in pathogenicity and diagnosis are crucial in control of avian influenza outbreaks. The Nonstructural [NS] gene and its protein products [NS1 and NS2] are important as diagnostic marker, life cycle and pathogenicity of AIVs. The NS gene of five strains, isolated from 1998 to 2010, were completely sequenced and analyzed. All of the examined strains were composed of 890 nucleotides with 230 amino acids. In this regard, only two Iranian strains from GeneBank had 217 amino acids in NS 1 protein. All Iranian H9N2 strains subdivided into two distinct sublineages including I and II. Comparative analysis of NS genes of Iranian strains showed that since 2003, they might have originated from Pakistan H7N3 strains; whereas from 2008 they could be originated from Pakistan H9N2 strains. Although the low pathogenic H9N2 subtype has been permanently circulating from 1998 to the present in Iran, phylogenetic analysis of NS genes revealed that sublineage II has circulated more in poultry industry of Iran. These epidemio-logically variations could be related to vaccination pressure due to massive vaccination or NS gene reassortment in rural and backyard chickens