Molecular Evolution And Lethality On Mice Of H9N2Influenza Virus Isolated From South Of China

Avian influenza is a kind of epidemic infectious disease which is caused by Orthomyxoviridae, type A avian influenza virus. It is listed as a fulminating infectious disease, type I by the World Organisation for Animal Health. Avian influenza viruses have broken out many times in a worldwide range since it was first detected in1878. It not only infected domestic poultry, wild birds, and some species of mammals (such as pigs), but also subtype H5N1infected humans in Hong Kong in1997, which resulted in the deaths of several people. It has caused huge economic losses to poultry industries as well as damages to human health.In total, there are16subtypes of the Hemagglutini gene (HA1-HA16) and9subtypes of the Neuramindase gene (NA1-NA9). Lethality in different subtypes of avian influenza viruses is very different; only some of them have caused outbreaks in birds and domestic poultry. The H9N2subtype of avian influenza virus is prevalent in many species. Its natural hosts vary among domestic fowls, many kinds of wild birds, some kinds of mammalians, and even human. Wild birds are considered to be the natural reservoirs for avian influenza A viruses(禽流感).This subtype is also regarded by the World Health Organization (WHO) as the next potential avian influenza subtype that may have high prevalence in the future, and which may bring huge damages upon global economies and public health. Based on those reasons, we discuss the characterization, sequence data and evolution of those isolated H9N2viruses in our study.During active influenza surveillance in southeast China, we isolated and characterized17H9N2viruses from four species of ducks, Anas penelope, Phasianus colchicus, Anas poecilorhyncha and Anas platyrhynchos, and named as:A/Anas penelope/Shanghai/23/11(H9N2), A/Phasianus colchicus/Jiangxi/30/11(H9N2), A/Phasianus colchicus/Jiangxi/31/11(H9N2), A/Anas poecilorhyncha/Jiangxi/32/11(H9N2), A/Anas poecilorhyncha/Jiangxi/33/11(H9N2),A/Anas poecilorhyncha/Jiangxi/34/11(H9N2), A/Anas poecilorhyncha/Jiangxi/35/11(H9N2),A/Anas poecilorhyncha/Jiangxi/36/11(H9N2), A/Anas poecilorhyncha/Jiangxi/37/11(H9N2), A/Anas platyrhynchos/Jiangxi/38/11(H9N2), A/Anas platyrhynchos/Jiangxi/39/11(H9N2), A/Anas platyrhynchos/Jiangxi/40/11(H9N2), A/Anas platyrhynchos/Jiangxi/41/11(H9N2), A/Anas platyrhynchos/Jiangxi/42/11(H9N2), A/Anas platyrhynchos/Jiangxi/43/11(H9N2), A/Anas platyrhynchos/Jiangxi/45/11(H9N2), A/Anas platyrhynchos/Jiangxi/46/11(H9N2).All8segments (HA, NA, M, NP, PB1, PB2, NS and PA) forming11of17isolated avian viruses were amplified, cloned and sequenced successfully. Phylogenetic analysis of the whole genome indicates that all isolates share high homology with each other and with two human H9N2isolates (A/HongKong/35820/2009and A/HongKong/33982/2009). All eleven isolates appear to belong to a novel reassortant H9N2genotype of G1-like viruses, containing Ck/Bei-like NA genes, Y439-like PA genes and six other G1-like genes (HA, M, NP, PB1, PB2, NS and PA).We chose one isolated H9N2virus (A/Anas platyrhynchos/Jiangxi/39/11) based on sequence data to infect specific pathogen free mice (BALB/c) to assess the pathogenicity of these isolates in mice. Data from histological section and real-time PCR demonstrated that these viruses could replicate efficiently in the lungs and tracheae of BALB/c mice and caused mortality in20-40%of infected groups after3-6days. Our results confirm that wild ducks play a role as reservoir hosts for the reassortant H9N2genotype. Because the results also suggest that these viruses are capable of establishing lethal mammalian infection, urgent attention should be paid to surveillance for these strains in humans.