Surveillance On Avian Influenza Viruses In Wild Birds In Shanghai And Phylogenetic Analysis Of Viral Genes

Wild birds are the natural reservoir of Avian Influenza Virus(AIV). Waterfowl persists the major gene pool of low pathogenic avian Influenza virus (LPAIV) in nature.2006-2008, a surveillance program targeting AIV in wild birds of Shanghai was cairred out. A total of 1674 wild birds from 6 Orders,90 species were sampled in Shanghai to detect AIV and seroprevlance of AIV antibodies.55 birds from 3 Orders,7 species were detected bearing influenza A viruses and yielded viral prevalence rates of 7.79%,3.70% and 0.19% in Order Anseriformes, Gruiformes and Passeriformes, respectively. The bird species of the highest viral prevalence rate was Scaly Thrush (Zoothera dauma)(33.3%), followed by Spot-billed Duck (Anas poecilorhyncha)(25.0%) and Mallard (Anas platyrhynchos)(12.9%). The predominant HA and NA subtypes identified in these strains were H9 and N2.27 of 90 species were detected bearing serum antibodies against AIV. The average anti-M1 rate was 18.5%. The average anti-H5 rate was 7.13%. The seroprevalence rates in order: Gruiformes>Anseriformes>Ciconiiformes>asseriformes. Coinfections or superinfections of the same H9 subtypes were observed in wild ducks as an dominant subtype in our study. Phylogenetic analysis of viral genes on HA showed that H9 sequences in our study belonged to BJ/1/94-like genotype (poultry) and Y-439-like (wild bird) genotype. The infections of BJ/1/94-like H9 strains in wild ducks had significantly correlations with coinfections with the other genotype (Y-439 like). Phylogenetic analysis of 35 matrix (M) genes sequenced in this study showed that 8 strains belonged to a Eurasian avian lineage and 2 strains clustered with recently circulated human isolates. The other 25 strains had the highest homologies with the earliest strains of Influenza A viruses in humans (A/WSN/1933 H1N1 and A/Puerto Rico/8-1/1934 H1N1), in which 23 strains clustered together to form a unique sublineage and shared a major branch with human isolates. The abundance of this rare genotype of M gene suggested its well adaption in both poultry and wild ducks so as to probably gain a survival advantage in coinfections. Above all, wintering waterfowl, among all wild birds, is the major vector of AIV in Shanghai. The local epidemiological situation was characterized by the remarkable high viral prevalence, H9N2 as the predominant subtype with potiential epidemic risk and the complex coinfections.