| It was reported firstly in February 19,2013 that people infected with H7N9 subtype of influenza in China. The H7N9 has been three waves of the epidemic. It is a threat to people's health, and China's poultry industry was also caused huge economic losses. So the study on epidemiology and pathogenicity for H7N9 has important practical significance.In order to understand the prevalence of H7N9 viruses in poultry interface, we have collected 8770 swabs and environmental samples and 28 H7N9 virus were isolated and identified in 2013-2015, including 2 strains from ducks, 2 from the environment and 24 from chicken. The total separation rate was 0.32%. It was collected from Jiangsu, Guangxi and Guangdong Province. Four viruses was isolated from farms and 24 from live poultry markets.To study the genetic evolution of H7N9 virus, we study on the 28 H7N9 virus from poultry and 1 H7N9 from human. phylogenetic analyses of the HA genes confirmed that all of the third wave(W3) avian H7N9 viruses in Guangdong Province were descended from the viruses of the second wave(W2). Viruses of W3 clustered into two major clades,designated as W3-a and W3-b, all of which emerged from the W2 clade. The W3-a clade contained viruses detected in Dongguan, Guangzhou and Huizhou city, while clusters of viruses from Guangdong, Hong Kong and Guangxi, suggested that W3-a viruses from poultry were simultaneously prevalent in this locality from humans. But the A/Chicken/Guangdong/GZ068/2015(H7N9) showed significant genetic divergence. The W3-b clade contains viruses detected in Shanwei and Chaozhou city, including theA/Chicken/ Guangdong/CZ145/ 2015(H7N9), A/Chicken/Guangdong/SW153/2015(H7N9)and A/Chicken/ Guangdong/ SW154/2015(H7N9), clustered with strains detected in Xinjiang, Fujian, Guizhou and Jiangsu from humans or environment during the third wave, suggesting regional spread of the viruses, probably by regional transporting of poultry or by migratory birds. Phylogenetic analysis of the N9 neuraminidase(NA) genes revealed a similar topology to that of the H7 HA tree, with the wave 3 viruses separated into two corresponding clades.Internal genes have showed more regional characteristics which may be related to transportation across provinces for live bird trade or to migratory birds.We have conducted the mutation analysis of critical and apparent amino acid residues of H7N9 virus isolates. All H7N9 viruses isolated have an amino acid PB2-627 E,PB2-701 D, HA-226L(H3 numbering), NA-289R(N9 numbering), M2-31 N and HA-cleavage sites- PEIPKGRG. Four H7N9 viruses have HA-186V(H3 numbering) and others have HA-186A(H3 numbering).To understand the pathogenicity of H7N9 virus in chicken, we chose four H7N9 virus for challenging to SPF chicken. The results showed that four H7N9 viruses have weak pathogenicity. The chickens were not showed significant clinical symptoms after challenging. Only G1 group showed a slight reduction in food intake, including two chickens depression at the 4 day after challenging. But the chickens had returned to normal two days later. The H7N9 virus can spread through cohabitation. Four H7N9 viruses have exhibited different tissue tropism and the ability to replicate in chickens. G1 strain has a slightly stronger ability to replicate in chickens. All strains replicate easily in the lung tissue.Biopsy results showed that four H7N9 virus had weak pathogenicity to visceral tissues and the severity of the lesions showed lung> kidney> cecal tonsil> liver> spleen. |
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