Phylogenetic Analysis of Avain-like H1N1 Swine Influenza Virus in Shaanxi Province

Objective)The prevalence and transmission of swine influenza in Shaanxi Province were studied.(Method) Nasal/tracheal swap samples were randomly collected from apparently healthy pigs in farms and slaughterhouses in Shaanxi province between October 2011 and May 2012. The samples were firstly separated by SPF chick embryos, and the HA-positive samples were identified as swine influenza virus using RT-PCR. Then, the full genomes of these isolates were sequenced and used to re-construct phylogenetic trees with software MEGA 4 and analyze genetic variations. (Result) Six H1N1 influenza viruses were isolated and identified among 500 samples, with isolation rate of 1.2%. The full length genomes were obtained from six isolates, with nucleotide similarity of 98.3-99.1% . Phylogenetic analysis showed that six H1N1 virus isolates were located into the lineage of avain-like H1N1 swine influenza viruses. The nucleotide similarities were 97-99% between six isolates and SIVs from Jiangsu, Liaoning, Shandong, and Hong Kong. The mutated nucleotides of eight gene fragments for six isolates were detected at receptor binding sites and potential glycosylation sites. These genetic variations will affect antigenicity, host adaptability and virulence of the viruses. (Conclusion) The H1N1 swine influenza virus were firstly isolated from apparently healthy pigs in Northwestern China, and six full length genomes of these isolates were obtained. Phylogenetic analysis suggested six isolates were avain-like H1N1 swine influenza virus. Mutations were also detected in some amino acid sites of these isolates.