Pandemic Strain Characteristics And Geneticvariability Of H9N2Subtype Of Avian Influenza Virus

H9N2subtype avian influenza virus exists widely in the world,although the subtype belongs to low pathogenic strains, but can cause the host’simmune suppression. H9N2subtype avian influenza have a synergetic effect withother pathogenic microorganism, which can cause the increased death rate in diseaseof chicken, resulting in serious economic losses to the poultry industry. Since H9N2subtype avain influenza was first isolated in China in1994, the epidemic areas ofH9N2subtype avain influenza was constantly expanding. Before2010, H9N2mainlyprevailed in areas such as Hubei, Zhengjia.etc. After the winter of2010, the epidemicarea expanded to other areas,such as Guangdong, Guangxi, Fujian, Yunnan,southwest, Anhui, especially in Guangdong, Hubei, where H9N2spreaded quickly. Sofar, this subtype distributed throughout the country. In this paper, HA, NA gene ofH9N2subtype avian influenza virus were sequenced and analyzed, which wereisolated during2009to2012, and8strains selected from isolated virus were used tostudy the cross protection. The above experiments have important significance inaspects of epidemiology and prevention and control of avian influenza H9N2.1. The isolation, identification and analysis of HA gene mutation of H9N2subtypeavain influenza virus.We collected pathological material of disease which were suspected H9N2subtype influenza virus infection from different areas in China during2010to2012.then the virus were isolated and identificated. And the HA, NA gene of the isolated16strains and the laboratory preservation of the same subtype(the isolated3strains in2010) were sequenced and analyzed.The results showed that the nucleotide homology of HA gene of the isolated19strains viruses during2010to2012was between the93.7%-99.9%, and the aminoacid homology was between95.2%-100%. Almost of the strains isolated in2012, theamide-containing amino acid(Q: glutamine) in the235loci turned into asulfur-containing amino acids(M: methionine), which may be the cause of variation ofbiological characteristics of the strains isolated in2012. but the cleavage site (335-341aa) of the amino acid sequences are RSSR↓G, which are consistent with the featuresof cleavage site of amino acid sequence of low pathogenic avian influenza. The nucleotide homology of NA gene was between the93.2%-100%, and theamino acid homology was between94.4%-100%. There are9nucleotides deletion in187-195amino acid site in clinical isolates, resulting in63-65deletion in amino acid,which are consistent with the most clinical isolates. There are mutation in some aminoacid sites of NA gene of the clinical isolates in2012compared with the previousisolates. And these mutations may cause difference of biological characteristics of theclinical isolates in2012.Phylogenetic tree analysis showed that clinical isolates showed obvious cluster inrecent years. Clinical isolates showed obvious differences in evolution during2010-2012.1. Cross protection tests of H9N2subtype isolates from2009to2012.The popular clinical isolated strains in recent4years were used to study the crossprotection tests, a strain of good cross protection was selected. The inactivatedvaccine of this strain can be against6strains of8isolates in infection, but not provideprotection for the A022-2012strain and ZC-2011strain in infection. Moreover, theinactivated vaccine of8isolated strains can not provide protection for A022-2012ininfection, including the inactivated vaccine made by itself. The ZC-2011strain can beonly protected by the inactivated vaccine made by itself.