Analysis on characteristics of HA1 gene of Influenza virus strains isolated in Zhejiang province

  Objective   To study the characteristics of HA gene of the subtype A3 influenza viruses isolated in the influenza outbreaks in Zhejiang province in recent two years.To know the mutation of influenza viruses in Zhejiang Province and the protectire effect of the vaccine strain recomended by WHO.

  Methods   Respiratory specimens were collected from the influenza like cases in 2003~2004 in Zhejiang province and the influenza virus were isolated from the specimens, A3 influenza viruses were extracted.Their HA1 genes were amplified by reverse transcription polymerase chain reaction(R T-PCR), The PCR products were sequenced, The data obtained were analysed with the software DNAMAN and Eio Edit.

  Results   The nucleiotides of HA1 region in the strains all were 987bp long and the deduced amino acids were all 329, there were no deletion and insertion in the nucleiotides.Accordingly, the point mutation percent was 0.8% ~1.3%.The strain isolated in 2003 had only 95.6% ~95.9% identity in nucleiotide sequence compared with A/Moscow/10/99 vaccine strain recommended by WHO at that time, and besides, there were 20 amino acids which had changed and six variant amino acid were found locating in the antigenic determinant sites A and B.The strain isolated in 2004 had 98.6%~99.1% identity in nucleiotide sequence compared to A/Fujian/411/2002(A/Kumamoto/102/2002, A/Wyoming/3/2003)vaccine strain recommended by WHO at that time, only 3~6 amino acid had changed.In the phylogenic tree, the strains isolated in 2003 and 2004 belonged to the same type which were near to the vaccine strain recommended by WHO in 2004 and far away from the vaccine strain recommended by WHO in 2003.

  Conclusion   The antigenic drift of influenza A3 of Zhejiang province had occurred which connected with the popularity of influenza in the province.The vaccine produced by the influenza A3 vaccine strain recommended by WHO in 2003 was of no protective effect to the influenza of the province, and the vaccine produced by the influenza A3 vaccine strain recommended by WHO in 2004 had good protective effect to the influenza in Zhejiang province.