OBJECTIVETo understand the HA1 genetic variation characterization of influenza virus subtype H3N2 circulated from 2001 to 2006 in Liaoning local area.

METHODSViral RNA was extracted and transcribed into cDNA by reverse transcriptase and amplified by PCR. The product of PCR was purified by QIAgen purification kits,and sequenced by ABI 3100avant. The sequence data were analyzed phylogenetically by Sequence software with epidemic records. Finally, the phylogenetic trees were drawn according to deduced amino acid sequences of influenza virus H3N2 from 2000 to 2006 in the NCBI database.

RESULTSThe seven HA1domain sequences of H3N2 influenza viruses circulated from 2001 to 2006 in Liaoning local area had been analyzed. Compared with WHO 2004-2006 H3N2 vaccine A/California/7/2004, 12 bases had changed, 4 positions had amino acid substitution in 62 * > E, 182 T > 1,224 S > A,225 C > Y. 224 and 225 are RBS (Receptor binding site). The homology is lower than 98%. Phylogenetic tree showed Liaoning H3N2 2006 strains and Zhejiang 2005 strains were similar to WHO Northern hemisphere winter 2006-2007 Vaccine A/Wisconsin/67/2005 (H3N2)-like virus and grouped together to form an independent cluster even though several bases were still different.

CONCLUSIONThe HA1 domain of HA gene of influenza viruses (H3N2) isolated from 2001-2006 in Liaoning local area showed base mutation, amino acid sequence difference compared to A/California/7/2004 (2005-2006 vaccine), suggesting it might be the main cause leading to the spread of influenza. The sequence analysis showed Liaoning 2006 H3N2 strains were similar to those from Southern area which suggested that further surveullance should be conducted to monitor the virus mutation in circulation.