Evolution Of H9N2 Influenza Viruses In Mainland China And Selection Of Vaccine Candidate

H9N2 avian influenza virus (AIV) is prevalent in whole world and recognized as one of the main poultry diseases. In Mainland China, H9N2 avian influenza virus was firstly isolated from chickens in Guangdong province in 1994, and then H9N2 AIV circulated widely in the domestic poultry and had caused great economic losses in China. Also, H9N2 avian influenza poses continuing threat to both the animal and human public health.Previous studies have systemically analyzed representative H9N2 avian influenza isolates from poultry in Mainland China during 1996~2002, and revealed that all of the viruses originated from CK/BJ/1/94-like virus. In order to consecutively observe the change of the H9N2 AIV in Mainland China, 51 representative H9N2 subtype viruses isolated from poultry in Mainland China during 2005~2009 have been sequenced and analyzed genetically in this study. Our results showed that all HA genes of 51 viruses bear the CK/BJ/1/94-like. 35 of 51 viruses bear the CK/BJ/1/94-like NA genes, and the others bear the G9-like NA genes, indicating that CK/BJ/1/94-like virus were still predominant in H9N2 subtype influenza epidemic in Mainland China. But, in the CK/BJ/1/94-like HA genes, 51 viruses form 4 different groups, under 93.9%homology among 4 groups and 3 groups in CK/BJ/1/94-like NA genes, which indicate the prevalent CK/BJ/1/94-like vary a lot. Viruses isolated in different provinces and from different hosts share large homology which shows H9N2 avian influenza viruses may be transmitted from one place to another, even circulating in whole china, and from one host to another. This transmission cause great difference in H9N2 avian influenza control.The amino acids of 51 viruses cleave site are -R(K)S(A)SR/GL-,no cationic amino acid insert, showing typical character of low pathogenic avian influenza. Amino acids in the receptor-binding sites of the HA were associated with the receptor binding specificity. All the receptor-binding sites have no big change, especially 226 site, and 50 0f 51viruses is 226Q, not 226L, having no preference to binding to SAα2, 6Gal moieties in human cell. 44 of 51 viruses have additional potential glycosylation sites at 324 near the cleave sites of HA may be associated with cleave character. G9-like of NA gene have a 9 bp deletion, and CK/BJ/1/94-like have no.Vaccination plays a large role in avian influenza control and prevention in china. In this study, prevalent vaccine strains were selected from fifteen H9N2 subtype avian influenza viruses isolated from eight provinces of China mainland during 2008 by antigenic analysis and immune efficacy, and 6 viruses are chosen as prevalent vaccine candidates. When immunized SPF chickens were inoculated intranasally with 106EID50 of homologous and heterologous avian influenza H9N2 virus, oil-emulsion inactivated vaccines prepared from CK/HuN/174/08 and CK/HuN/33/08 strains can not only completely protect SPF chickens from challenge with homologous H9N2 viruses, but also the 2008 heterologous isolates. So CK/HuN/174/08 and CK/HuN/33/08 were chosen as the ideal inactivated vaccine candidates against H9N2 avian influenza.