ABSTRACT
Objective To understand the evolutionary characterization of hemagglutinin (HA)gene of pandemic H1N1 influenza virus in Guangdong during 2009-2011. MethodsWe selected 83 pandemic H1N1 strains isolated in Guangdong during 2009-2011. The HA1 genes were sequenced and analyzed comparatively by Bioedit 7.0 and MEGA 4.0. ResultsThe evolutionary rate of Hal gene of pandemic H1N1 and seasonal H1N1 viruses was 5.2×10-3 substitutions/site/year, higher than that of seasonal H1N1 viruses. Most amino acid changes in HA1 molecules accumulated on the surface of the molecule and were partly located in antigenic sites. Two fatal infections were detected with a mutation at HA residue 222, in one virus with a change D222G, and in one virus D222N. ConclusionThe phylogenetic analysis demonstrates that the influenza epidemic in Guangdong at the beginning of 2011 are due to occurrence of genetic changes of pandemic H1N1 virus. The amino acid change at residue 222 of the HA1 are likely to be associated with severe or even fatal illness.