Genetic Analysis on NA Gene of Influenza A_3 Strains Circulating in Zhejiang Province in Recent Years

Objective To illustrate the relation between the variation of NA gene and the prevalence of Influenza through sequence alignment of NA gene among the Influenza A_3 strains circulating in Zhejiang Province in recent years.Method NA gene of the representative strains of Influenza A_3 isolated in outbreaks during 1998-2005 in Zhejang Province were amplified by reverse transcription polymerase chain reaction(RT-PCR).PCR products were purified and sequenced,then data were analyzed with biologic software bioEdit.Results Thirteen representative strains of Influenza A_3 were isolated from the outbreak in recent years,which NA gene were all 1338bp,amino acid were all 446.During 1998-2005,22 amino acid variated in NA gene of Influenza A_3.Especially during 1998-1999 and 1999-2002,9 amino acid have variated in NA gene.After 2002,according with the analytic results of phylogenic trees of NA gene,the variation of Influenza A_3 become balanced.In addition,there are some differences between the vaccine strains recommended by WHO and circulating strains.However,vaccine strains recommended by WHO accorded with the circulating strains primely after 2003.Conclusion In recent years,antigenic drift of NA gene may occur on Influenza A_3 circulating in Zhejiang Province,suggesting the cause of the two Influenza outbreaks during 1999-2005 may due to the antigentic change effected by the variation of the Influenza isolates.