Analysis of the Antigenic and Genetic Characteristics of Influenza Virus Subtype A_3 Circulated in Sichuan Province During 2006～2007

Objective To study the genovariation and antigenicity status about hemagglutinin of influenza virus subtype A3 circulated in Sichuan province;compare the genic differences on HA1 regions between influenza virus subtype A3 circulated in Sichuan province and influenza vaccine strain of subtype A3(A/Winsconsin/67/2005(H3N2))recommended by WHO for northern hemisphere in 2006～2007 so as to provide theoretical basis for evaluating the immunization effect of influenza vaccine.Methods The throat swab from the suspected influenza cases were collected from suspected epidemic influenza areas and the sentinel hospital monitored in Sichuan,and virus were isolated by using MDCK cells.The influenza virus isolated strain collected from different time and locations was identified to be influenza virus subtype A3 by hemagglutination inhibition test,then the isolated strains were performed one-way hemagglutination inhibition test;the viral nucleic acid were extracted to amplify the HA1 regions of HA by using RT-PCR,and the amplified products were sequenced to deduct the amino acid sequence;the sequence of isolated strains was compared with the sequence in HA1 of influenza vaccine strain of subtype A3(A/Winsconsin/67/2005(H3N2))recommended by WHO for northern hemisphere in 2006～2007,followed by signature analysis of the gene evolution.Results In line with results of one-way hemagglutination inhibition test,the variance of hemagglutination inhibition valence showed to be less than 4 times difference when the antigenicity of influenza virus subtype A3 compared with type strain of influenza virus subtype A3 in China(A/Yunnan/1145/2005 and A/Donghu of Jiangxi/312/2006).The results of nucleotide and amino acid sequence demonstrated that the similarities of nucleotide and amino acid sequence were 99.59% and 99.47% respectively.Just 4 to 6 amino acids sites replaced,which involved 2 antigen determinants.Conclusion There was no significant mutation of antigenicity and genetic characteristics of influenza virus subtype A3 circulated in Sichuan during 2006～2007.