Epidemiological Investigation Of Birdflu Virus Infection In Migratory Waterfowl In China And ELISA For H5 Subtype Avian Influenza Virus In Duck

Avian influenza (AI) is caused by influenza A virus that belongs to the family Orthomyxoviridae, genus Influenza A. It rapidly infects poultry and causes multiorgan systemic disease when it breaks out and leads to high rate of morbidity and mortality, avian influenza viruses (AIV) also have a wide range of susceptible hosts in nature. Since avian influenza virus was first identified in Italy in 1878, it continued to break out in various countries and led much economical losses. Furthermore, occurrences of direct bird-to-human transmission of AIV have increasingly been reported in recent years, culminating in the ongoing outbreak of influenza A virus (H5N1) among poultry in several asian countries with associated human infections. AI is a persistent potential health threat to both domestic and human species as well as wild species. It generally accepted that waterfowl play an important role in the generation, spread, and enzootic transmission of AI.It is generally accepted that wild aquatic birds provide a natural reservoir of avian influenza A viruse and play an important role in their ecology and propagation. We investigated the avian influenza A virus in wild waterfowl which migrate across China. From 2004 to 2005, a total of 458 serum samples and 1052 swab samples were collected from 15 kinds of migrated wild aquatic birds distributed in seven wildlife reserve refuges in China. In the HI assay, most of the test sera were negative for the 13 subtypes of AIV, while some species such as Relict Gull, Little Egret, Black-crowned Night Heron, Bar-tailed Godwit, Whimbrel had low-level antibodies against AIV (subtype H2, H9, H10). Notably, no avian influenza virus had been isolated from the swab samples except bar-headed goose. The isolated virus is H5 subtype avian influenza virus which identified through HI reactivity. Antigenic analysis showed that antigenic epitopes of the Qinghai virus is similar to the A/Chicken/Jiande/1218/2001 virus and the A/Duck/Jinhua/0226/2002 virus.The eight full-length genes, including the 5' and 3' ends of H5N1 subtype Avian influenza virus (A/Bar-headed Goose/Qinghai/0510/05 (Bh H5N1) ) were amplified using the universal primers and H5 specific primers. The amplified segments were cloned into the pMD18-T vector respectively. Three to five positive clones of each gene were sequenced and the the full-length sequences of the AIV genome were obtained. The phylogenetic analysis revealed that the isolated AIV strain was highest homology to CK/ST/4231/03 and Peregrine faclon/HK/D0028/04, and different from A/Goose/Guangdong/3/97 and A/Goose/Guangdong/1/96 in the eight genes...