Antigenic variations of human influenza virus in Shiraz, Iran.

Purpose: Influenza virus is a major cause of human respiratory infections and responsible for pandemics and regional outbreaks around the world. This investigation aims to determine the prevalent influenza genotypes during 2005-2007 outbreaks in Shiraz, the capital city of Fars province, southern Iran and compare the results obtained with those of previous study. Materials and Method: Of the 300 pharyngeal swabs collected from influenza patients, 26 were found to be positive by culture and hemagglutination (HA) assays. Typing and subtyping of the isolates carried out by using multiplex RT-PCR and phylogenetic analysis performed on isolated HA genes using neighbour-joining method. Result: Out of 26 positive isolates 12 and 14 were H1N1 and H3N2 respectively. The phylogenetic and amino acid sequence analyses of our H1N1 isolates showed 99-100% genetic resemblance to A/NewCaledonia/20/99 (H1N1) vaccine strain. Most of the Iranian H3N2 isolates varied form A/California/7/2004 vaccine strain in 20 amino acids of which positions 189,226 and 227 were located in antigenic sites of HA1 molecule. These substitutions were not observed in any of the H3N2 subtypes from the same region reported previously. Conclusion: The H3N2 subtype strains prevalent during the 2005/7 influenza outbreak in southern Iran demonstrated a drastic antigenic variation and differed from A/California/7/2004 vaccine strain. The H1N1 subtypes showed a notable resemblance to A/NewCaledonia/20/99 vaccine strain and therefore were predicted to be capable of conferring sufficient immunity against H1N1 subtypes.