Isolation And Identification Of H1N1Swine Influenza Virus In Jiangsu Province And Pathogenicity On Mice

Swine influenza (SI) is a highly contagious respiratory disease caused by A, B, C swine influenza virus. Several pandemic influenza viruses originated from pigs. Swine are susceptible to infect with both avian origin and human origin influenza viruses, because they have a-2,3sialic acid receptors and α-2,6sialic acid receptors. Novel reassortant influenza viruses can be generated in pigs by reassortment of influenza viral gene segments that leads to the "mixing vessel" theory. The three pandemic events of influenza in humans (H1N1pandemic in Spain; H1N2pandemic in Asia; H3N2pandemic in Hong Kong) are related to swine and SI. Therefore, the public health concern calls for careful surveillance to H1N1influenza viruses.The novel swine-origin A influenza virus outbreaks in Mexico in March2009and soon becomes pandemic around the world. Susceptible population is mainly students and adolescents. Later researches found that there is substantial evidence that the influenza viruses in Mexico Pandemic in March2009are novel reassortant influenza viruses of avian, swine and human influenza viral RNA segments. For the above reason, that surveillance of swine influenza virus H1N1in Jiangsu Province has important significance to prevent the occurrence of major epidemic and reduce the pecuniary loss.In order to surveille H1N1epidemic in pigs in Jiangsu and discover whether it contributes to epidemic or pandemic potential, and to real the characteristics and the pathogenicity of the viruses, one thousand and twenty-nine nasopharyngeal swabs of swine in northern, middle and southern of Jiangsu Province (i.e. Yancheng, Yangzhou and Wuxi) were collected in slaughterhouse, farms and infected swinery to isolate viruses from Jan2010to May2010. There were eleven strains of H1N1subtype and two of H9N2subtype swine influenza viruses (SIV) isolated and identified. Here, we sequenced the entire genomics of eight strains of H1N1SIVs and analyzed the evolution of them, finding that all the eight SIVs were low pathogenic, triple Reassortants and similar to A/California/04/2009. The results suggested that the H1N1influenza virus in2009might present in swine population. Furthermore, compared with the strain A/California/04/2009, all genes have not recombined, but two sites of hemagglutinin (HA) protein bond with the sialic acid (SA) receptors have mutated (D225G of three strains, Q240R of five strains) resulting in enhancement of the ability of binding with the Saa2,3Gal receptor, and the eight potential glycosylation sites of NA protein of two strains have mutated (Q50P) leading to the deficiency of the potential glycosylation sites. All of those may be the virus adoption in swinery and the novel H1N1SIV may become the main population in swine of our country by mutation s for adoption.To explore the pathogenicity of H1N1influenza viruses isolated from swine, we carried out experiments on ICR mice with a randomly selected strain of H1N1influenza viruses namely A/Swine/Jiangsu/48/2010. Each mouse was inoculated intranasally with50μl at a dose of1×107.6850%embryo infectious dose (EID50) H1N1virus as challenged group and with50μl PBS buffer as the control group, we also set an exposed group to investigate the horizontal transmission of the test H1N1virus. Collected data of the body weight of each mouse was recorded for an interval of24h post-challenge, and in the3,7,11and14days post-challenge, one mouse of each group was euthanized, the histopathology of heart, liver, spleen, lung, kidney was observed and virus isolation was done, the data showed that mice from challenged group and exposed group had weight loss in different degree at early period and began to recover at later period. The lesions mainly in the lung of the challenged mice were observed. The H1N1virus was recovered from the tissues of euthanized mice from3to7days post-challenge,while was not recovered after11days post-challenge. A similar, moderate histopathological changes were observed in the mice of the exposed group, and no virus was isolated in the mice for the whole period. These results showed that the H1N1virus had a tendancy to be transmitted among ICR mice, however,the direct evidence for this transmittion need further study.