Genetic characteristics of influenza A3 virus circulated in Huzhou, 2009-2012

Objective To understand the genetic variation of hemagglutinin(HA) and neuraminidase(NA) of influenza A3 virus circulated in Huzhou during 2009-2012. Methods The RNA of 11 influenza A3 virus strains, circulated in Huzhou during this period, were extracted. The HA1 and NA regions were amplified and sequenced. All the sequence data were analyzed using MegAlign. Results The HA1 and NA regions of all strains belonged to 987nt and 1362nt, encoding protein of 329 and 454 amino acids respectively. The strains shared amino acid homology of 94.7%-99.9% and 96.2%-100.0% in HA1 and NA regions respectively, the variation in HA1 region was greater than that in NA region. Multi amino acid loci variation had occurred compared with the influenza A3 virus strains isolated in previous years. In addition, there were some differences between the vaccine strains recommended by WHO and the circulated strains. Conclusion Obvious genetic variation had occurred among the strains of influenza A3 virus isolated in Huzhou from 2009 to 2012. Genetic reassortment and antigenic drift seemed to be the major evolutionary mechanism of influenza A3 virus.