Investigation Of Avian Influenza Infections In Wild Birds, Poultry And Humans In Eastern Dongting Lake, China

Influenza A virus has a broad host spectrum, and can infect a variety of animals, including birds, horses, pigs, seals, and humans. Wild birds (mainly Anseriformes and Charadriiformes) are recognized as the natural reservoir of influenza A virus. All influenza A virus subtypes (H1～H16and N1～N9) have been identified in them. They preferentially replicate in the cells lining of the intestinal tracts of birds, and are excreted in high concentrations in their faeces, and contaminate the surroundings. The contaminated surroundings may result in efficient transmission to naive birds through the fecal-oral route. Wild Birds are distributed globally, and most of them are regular long-distance migrators, thereby potentially distributing LPAI viruses over long distances between countries or even continents. The systematical surveillance programs of AIVs in wild birds have been conducted in North America and Europe since1970s, which revealed that the outbreaks of avian influenza virus in poultry were closely related to the avian influenza virus circulating in wild birds. For example, there is a much higher rate of poultry infection with AIVs on migrating routes. In addition, the generation of HPAI viruses appears to be a phenomenon associated with adaptation of LPAI precursor viruses in wild birds to chickens or turkeys.AIVs have the strict host restriction. Occasionally, H5, H6, H7, H9and H10subtype AIVs can directly infect humans. Additionally, AIVs can infect humans through the "indirect way"-they reassorted with other subtypes influenza A virus circulating in humans. Terefore the knowledge of cross-species transmission mechanism of the AIVs among wild birds, poultry and humans are very vital for our prevention and control of AIVs. However, we still know little about these. There are lots of lakes, rivers and wetlands in China Mainland, which are important habitat for birds. Migrating birds migrated regularly between breeding sites and overwintering sites year by year. The East Dongting Lake is located at the East Asia-Australia migrating flyway, which is one of the largest lakes in China and the major staging and overwintering site for migratory birds. Moreover, a number of domestic duck farms existed in this region, and the domestic ducks were raised in a free-range style. Therefore the wild waterfowl and domestic ducks may share the commoon habitat, water and food, which provide the possibility for gene exchanging between different subtype AIVs circulating in wild waterfowl and domestic poultry. Little research of the prevailing situation of AIVs in wild birds and in poultry farms, therefore we selected the region for our research.To study the prevalence of wild birds, poultry and human infection with AIVs virus in Eas Dongting Lake region, a cross-section investigation was conducted by Chinese National Influenza Center, Hunan Provincial CDC and Yueyang CDC and Hunan East Dongting Lake Nature Reserve during November2011and April2012. A total of6,626environmental samples from wild birds and domestic ducks were collected, and1050serum samples of staff in Nature Reserve, fishermen in the lake, poultry workers in poultry farm were collected.Our results showed that the infection rate of AIVs in wild birds and domestic ducks were5.2%and5.3%, respectively, but there were no significant statistical difference between them. The detection rate of AIVs in wild bird faeces was significantly higher than l^ke water, which indicated that wild bird faeces were favorable for surveillance of AIVs in wild birds. Moreover we observed two peaks of AIV infection rate in wild birds and domestic ducks in December2011and March2012.46AIVs strains were isolated from fecal specimens of wild birds and domestic ducks, Nine HA and NA subtypes AIVs were isolated from wild birds, including22H9N2,5H1N5,3H5N2,2H1N8,2H6N1,2H6N2,1H1N2,1H7N7, and1H12N8. Three’HA and NA subtypes AIVs were isolated from domestic ducks, including3H5N1,2H4N2, and2H3N6strains.The total isolation rate is0.69%. The isolation rate in wild birds is0.72%, and the highest isolation rates in Anatidae and Charadriiformes were1.01%and2.22%, respectively, which was consistent with the conclusion of surveillance of AIVs in wild birds in North America and Europe. It suggested that the two kinds of birds may also the main host infection with AIVs in the region. The virus isolation rate of domestic duck is about0.58%, which is much lower than it in live bird markets. It may be related that the most samples were collected in the backyard farms.Molecular characteristics and phylogenetic analysis showed that most gene segments of46isolates belong to Eurasian gene pool. But22H9N2viruses are reasorted between North American and Eurasian gene pools. Their HA, NA, PA, and NS genes are derived from the North American gene pools, and antigenic analysis results suggested that the antigenicity of the isolates were significantly different from the viruses which have been dominant in domestic poultry in Eurasia and Africa. The events of inter-hemispheric exchange of viral genes were also found before, but its frequency was usually low. In addition, gene exchange of AIVs between wild birds or wild birds and poultry around the lake were found in several isolates. But the frequency and mechanism of the gene exchange and cross-species transmission need further study and continuous surveillance.To assess serologic evidence of infection with Highly Pathogenic Avian Influenza virus H5N1,1050serum samples were performed HAI assay and confirmed by MN assay. Whereas no positive serum contained antibody were obtained with two detection antigen which belonged to clade2.3.2.1and clade2.3.4, respectively. Three HPAIVs H5N1were isolated from domestic ducks in poultry farm in Yueyang County, which HA gene belonged to the clade2.3.2.1. The risk of human infection with HPAIV H5N1was low in the region, though it still needs to be alerted.In the study, we acquired preliminary understanding of the baseline of wild birds, domestic ducks and human infection with AIVs, and first report several subtypes of AIVs in the region. And the events of gene exchange may exist in part of the isolates of wild birds, and part of their genes showed high nucleotide similarity with the corresponding genes of AIVs that isolated in poultry, which indicated the events of gene exchange of AIVs between wild birds and poultry may exsit. Although the risk of human infection with HPAIV H5N1is low, but the risk of human infection with other subtypes of AIVs needs further research and analyze.