| Pig is one of the major hosts of influenza virus, and can be susceptible to both human and avian influenza viruses, which plays important role in shaping the current influenza ecology. The occurrence of the 2009 H1N1 pandemic influenza virus demonstrated that pigs could independently facilitate the genesis of a pandemic influenza strain. Swine influenza(SI) caused by swine influenza virus(SIV) is an acute and highly infectious respiratory systemic disease, and is an endemic and pandemic disease. The typical clinical symptoms of SI are cough, high fever, lethargy, and anorexia, nasal discharge, dyspnea, weight loss, high incidence of a disease but low mortality. SI could cause secondary infection or mixed infection, and further develop into the porcine respiratory disease syndrome, which will cause huge economic losses. The major subtypes of SI circulating in pigs are H1N1, H1N2 and H3N2.In order to investigate the epidemics of swine influenza viruses(SIV) and 2009 H1N1 pandemic influenza virus(H1N1pdm09) on pig farms in southern China(Guangdong province,Guangxi province,Jiangxi province,Hunan province and Fujian province), a total of 2,208 pig serum samples collected from 73 pig farms during Oct 2013 to Sept 2014 were dectected the antibodies against EA H1N1, H3N2 SIV and H1N1pdm09 virus and analyzed by the hemagglutination inhibition(HI) tests. The total positive surum rate was 57.42%(1,269/2,208).Higher seroprevalences were found in Guangdong province and Guangxi province(p<0.01).The seroprevalences of EA H1N1, H3N2 SIV and H1N1pdm09 virus were 22.51%, 32.97% and 26.49%, respectively. The geometric mean antibody titers of H1N1pdm09 virus was the highest(91.93±1.04, p<0.05). The prevalence of H1N1 and H3N2 SIV was characterized by a large peak in winter, and then sharply declined in the late winter(February). While the prevalence of H1N1pdm09 virus reached the first peak appeared in May, then declined and followed by another peak in September(p<0.01). Compared with piglets(19.63% and 23.29%) and finishing pigs(22.32% and 27.16%), the seroprevalences of antibodies against EA H1N1 and H1N1pdm09 virus in sows were higher, and were 25.93% and 28.04%, respectively. However, the seroprevalence of H3N2 SIV in piglets was relatively higher. These data provided reference basis for the prevention of swine influenza on pig farms in southern China.Vaccination is considered as the most effective mean of reducing influenza burden. So far, adjuvant inactivated swine influenza virus vaccine is the most widely used, and the technology to produce this vaccine is the most mature. Vaccine candidate strain not only should be able to breed in chicken embryo in a high level, but also should have good immunogenicity. In order to generate the embryo-adapted vaccine H3N2 virus, an eight-plasmid DNA transfection system has be developed. Candidate pandemic vaccine strains consisting of the circulating strain haemagglutinin(HA) and neuraminidase(NA) in an A/Puerto Rico/8/1934 backbone were generated through reverse genetics technique.The results showed that all gene of r L22/PR8 are consistent with the corresponding gene sequences of the PR8 virus and H3N2 SIV. After repliceted in 9-day-old SPF chicken embryos, the HA titer of the r L22/PR8 virus was raised to 210, and the result of EID50 was 1.78 x 109 EID50/m L. Besides, there was no chicken embryo dead. The results above indicated the r L22/PR8 virus was egg-adapted strain. The protective efficacy of this vaccine with adjuvant was evaluated in mice. Prime and boost inoculation of r L22/PR8 vaccine yielded high-titer serum HI antibodies for L22 in mice. This study has laid the groundwork for vaccine research and development. The r L22/PR8 virus coulde be considered as a vaccine candidate strain. |
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