Discussion On The Relationship Between The Swine Influenza Viruses And The Prevalence Of Influenza A/h3n2 In Zhejiang Province

Background and objectives:Influenza is an acute respiratory disease which was caused by influenza virus. Because of high genetic variation of the virus, it infected the population again and again with high incidence. The global epidemic of influenza A H1N1 virus in Spring 2009 become the world's attention once again. Because influenza A virus remains an important pathogen which threatens health of human in long time and China is the main resources of the new viruses, so deeply understanding the evolution and variation rule of influenza virus has very important meaning for prevention of influenza. Swine influenza is an acute respiratory disease which was caused by swine influenza virus. Pig is susceptible to avian and human influenza viruses and has been proposed to be intermediate host or"mixing vessel"for the generation of pandemic influenza virus. On the other hand, swine influenza virus could infect people and avian. Swine influenza surveillance is of great significance for veterinary and public health. In this assay, we investigated the phylogenetic relationship between swine influenza A/H3N2 virus and the representative strains of human influenza A/H3N2 virus isolated in the last ten years, through comparing the sequences within HA and NA genes.Material and methods:HA,NA gene of the representative strains of Influenza A/H3N2 isolated in the last ten years in Zhejiang Province were amplified by reverse transcription polymerase chain reaction (RT-PCR). PCR products were purified and sequenced, other HA1,NA sequences of H3N2 human and swine influenza virus in the corresponding period of time were downloaded from NCBI GenBank, then data were aligned and used to construct phylogenetic tree with biologic software bioEdit(version 5.0.9.1) and MEGA(version4.0).Results:The homologies on the HA domain between human representative strains (A/Zhejiang/10/98, A/Zhejiang/6/99 and A/Zhejiang/8/02) and the swine strains (A/SW/Ontario/130/97,A/SW/Hongkong/4361/99 and A/SW/Hongkong/74/02) are 99.1%, 99.4% and 99.4% respectively, and based on the NA gene, the homologies between human strains (A/Zhejiang/10/98, A/Zhejiang/6/99 and A/Zhejiang/8/02) and the swine strains (A/SW/Ontario/130/97, A3/SW/Henan/S4/01 and A3/SW/HongKong/411//02) are 98.2%,99.3% and 99.3% respectively. These showed that the two types of Influenza viruses were highly homologue, and even some of their homologies were higher than that amongst the contemporary human influenza A/H3N2 strains. The same results were shown in the phylogenetic tree.Conclusions:The human influenza A/H3N2 virus isolated in the last ten years in Zhejiang Province closely associated with some of the swine influenza virus strains, and their relationship should be further studied.