| Avian influenza (AI) is a kind of viral and infectious disease by A type influenza virus of orthomyxovirus family, which happens in poultry and wild avian usually. In the experiment, an avian H5N1 influenza A virus was isolated from chicken tissues infected. The 50% egg lethal dose (ELD50)titer of this AIV is 10-7.67 /0.lml. Eight-week-old chickens were inoculated by intranasal route with 0.2ml per chicken of the 1:10 dilution allantotic fluid of three H5N1 AIVs isolated from chicken (above mentioned) and duck and goose, respectively. In laboratory infectious, three chickens were taken out random on hours 12, 24, 36, 48, 72..and l68 postinoculation. Through observing clinical signs, examining gross and histopathological changes, examining the kinetics of virus replication in brain, lung, kidney, liver, spleen and muscles, and detecting the changes of antibody liter and 13 item serum biochemical markers, we study the pathogenicity of this three H5N1 AIVs.Although no clinical signs of disease were observed in H5N1 virus-inoculated chicken that died, gross and histopathological changes are more typical, such as hemorrhage in the squama of foot, gland-stomach ripple and the joint of two stomach, and degeneration and necrosis of cell components in the spleen, thymus, bursa, mecum tonsil, trachea, lung, duodenum pancreas, gland-stomach, liver, kidney and heart. Infectious virus could be detected in six tissues of above mentioned. In addition to some serum biochemical markers denote significant changes. The results indicate that this AIV is highly pathogenic and replicated to higher liters in chicken, which belong to extensive indulged virus. As with this H5N1 AIV isolated from chicken, the two H5N1 AIVs isolated from duck and goose produced similar systemic lesions in chicken following i.n. inculation, but the three H5N1 AIVs exist differences of pathogenicity in certain degree!...
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