Isolation And The Whole Genome Sequences Anaysis Of The H1N1SIV In Shaanxi Province

Swine influenza（SI）is one of the respiratory and difficult to be eradicated diseasecaused by swine influenza virus (SIV), which causes significant economic losses to livestocksand poses a serious threat to human health. During October2011to March2013，Swineinfluenza investigation was carried out in farms and slaughterhouses in Shaanxi in this study.The aim is to obtain the SIV isolates in Shaanxi and then understand the subtypes, geneticvariation and stealth infection of the SI in this region, which provide important reference datafor the SI research. Our experiment obtained the following results:1. Six H1N1SIVs were isolated and identified from apparently healthy pigs.Nasal/tracheal swap samples were randomly collected from apparently healthy pigs in farmsand slaughterhouses in Shaanxi province between October2011and May2012. The sampleswere separated by SPF chicken embryos affter conventional treatment, and the HA-positivesamples were identified using RT-PCR. Six H1N1SIVs were isolated in Shaanxi provincewith the isolation rate of1.2%.They were named as A/Swine/Shaanxi/s1/2011(H1N1); A/Swine/Shaaxi/s2/2012(H1N1);A/Swine/Shaanxi/sw/2011(H1N1);A/Swine/Shaaxi/s3/2012(H1N1);A/Swine/Shaaxi/s6/2012(H1N1); A/Swine/Shaaxi/sf/2011(H1N1).2. Phylogenetic analysis showed that the six H1N1SIVs isolates belong to avain-likeH1N1SIV lineage. Eight gene fragments of the six isolates were amplifid by RT-PCR, cloned,then sequenced and obtained the complete genome sequences, respectively. Comparison andanalysis of the nucleotide and amino acid variation by DNAStar software. Gene evolutionarytrees were builded by MEGA4. The results showed that the six isolates are all low pathogenicstrains with nucleotide similarity of98.3%～99.1%, and which were located into the lineageof avain-like H1N1swine influenza viruses. The nucleotide similarities were97%～98%between six isolates and SIVs from Jiangsu, Liaoning, Shandong, Hong Kong. The isolates A/Swine/Shaanxi/s2/2012(H1N1) and A/Swine/Shaanxi/s6/2012(H1N1) have high similaritywith influenza virus isolated from human in Jiangsu Province, which show that the virus caninfect the crowed. The mutated nucleotides of the isolates were detected at receptor bindingsites or potential glycosylation sites, and these genetic variations have affected the virulence,antigenicity, host adaptability and drug resistence of the viruses. 3. Serological testing showed that the H1N1SIV stealth infection rate reached31.6%from apparently healthy pigs. To fully understand the prevalence of SI in Shaanxi Province.1600serum samples were collected from apparently healthy pigs in twelve farms andslaughterhouses of seven regions between October2011to March2013. Using therepresentative isloate A/Swine/Shannxi/s1/2011(H1N1) as the test antigen after purified.Serological surveillance were carried out by HI and NT test. HI results showed that, thestealth infection of the H1N1SIV in healthy pigs in Shaanxi is16.7%～47.1%, average to31.6%, and indicated SI infections have significant seasonal differences, mainly occurs inSpring and Winter and NT results showed that93.3%of HI-positive serum samples havefulled neutralization capacity, indicating that the pigs have high infection H1N1SIV inShaanxi Province.