Abstract: The ducks are considered to be a natural reservoir for influenza viruses. Neither shows any clinical symptoms nor mortality when ducks infected with influenza virus. In order to assess the pathogenesis of the influenza A virus A/Goose/HLJ/QFY/03 (H5N1) isolated from a diseased geese farm, the SPF chickens and ducks were challenged by natural route, respectively. Challenge experiments demonstrated that the isolate was highly pathogenic both to chickens (IVPI=3) and ducks where it produced 75% mortality. Depression and marked nerologic dysfunction were common clinical manifestations of disease. Gross lesions included liver and splenomegly, hemorrhages; lung with severe acute congestion and hemorrhages; diffused enteric mucosa hemorrhages in alimentary tract. Histologic lesions were observed in multiple parenchymal organs and were characterized by congestion, hemorrhage, degeneration to necrosis or heterophilis infliltration. High titers of viruses were isolated from tracheal and cloacal swabs as well as multiple organs by 2-4 DPI (days post infection), and the viruses were confined only to pancreas after 7 DPI. This is the first confirmed H5N1virus isolated from domestic poultry that are lethal to ducks.

Key words: Avian influenza virus, Duck influenza, Goose-origin, H5N1 subtype