| From 2000, the epidemics of avian influenza(AI) resulted from avian influenza virus (AIV) caused severe disease and mortality of chickens, waterfowl-geese and ducks. During the epidemics, three different host-origin AIV strains named JC, ZM and SG, isolated respectively from chicken, muscovy, and goose, were selected and investigated for their pathogenicity. All of these three isolates were H5N1 subtype determined by serological test.According to the American standard which determines the highly pathogenic avian influenza virus(HPAIV), the three isolates were inoculated into 27-day-old chickens, 35-day-old geese, 30-day-old broiler-ducks 11-day-old muscovy ducks, 11-day-old Shaoxing-ducks and broiler-ducks 43-day-old pigeons via intravenous route respectively, and also 26-day-old quails and 29-day-old partridges were inoculate via intramuscular route. Within 10 days, the mortality rate of chicken and quail caused by the three isolates JC strain, ZM strain, SG strain were 100%. The death occurred within19-28hr, 15-39hr, 39-67hr in chicken, and 16-40hr, 16-63hr 48-88hr in quail. These isolates produced 62.5% 75% 50% mortality rate in partridges in 74-87hr, 24-87hr, 92-185hr. Mortality rate caused by JC strain, ZM strain in geese was 100% and 87.5% respectively, death occurred within 62-148hr and 39-109hr. In 11-day-old muscovy ducks, death rate was 62.5% caused by JC strain in 41-214hr and 75% in 61-214hr by ZM strain. One shaoxing-duck injected with ZM strain was dead 69hr postinoculation. No death occurred in pigeons and broiler-ducks, challenged with threeisolates, shaoxing-ducks challenged with JC strain and SG strain, geese and muscovies challenged with SG strain.The common clinical sign of the gallinaceous species before dead included depression,diarrhea,decreased feed consumption. Part of chickens, geese and muscovies showed some particular symptom such as nervous disorder, cyanosis of unfeathered skin. The most severe and consistent lesions in pathology and histopathology existing in brain, heart, liver, kidney, pancreas, lung, spleen, bursa, thymuses, enteric tract lymphoid, digestive tract include edema, congestion, hemorrhages, necrosis. In the immune organ, the lymphocyte decreased in number. The survived gallinaceous species remained clinically healthy, but light lesion can be observed in some organ. From the response of these poultry, it concluded that the three isolates are highly pathogenic to chickens and quails, non-pathogenic to pigeons and broiler-ducks, virulent to partridges. The JC strain and ZM strain show highly pathogenic to geese and muscovies while SG strain doesn't, ZM stain have virulence to shaoxing-ducks, JC strain and SG strain are not the case. Pathogenicity is determined by host and virus.The genomic RNA of the three AIV isolates were extracted and the HA gene of them were successfully amplified by reverse transcription-polymerase chain reaction (RT-PCR). The expected l.7kb-lengthed product were cloned into pGEMR-T vector and sequenced. The sequencing result showed that the length of the nucleotide sequence of the HA gene amplified were 1732bp containing the whole open reading frame of 1707 nucleotide that encodes a protein of 568 amino acid. The amino acid sequence of the cleavage site is R-R-R-K-K-R in these isolates, which reveal the molecular basis of the virulent AIV. Among these isolates, the homology of HA gene is 98.3%-99.2% in nucleotide sequence and 97.4%-98.8% in amino acid. The three isolates share 97.8%-99.0% identity of nucleotide sequence and 97.4%-98.6% identity of amino acid sequence with GD1/96 strain, GD3/97 strain. It can be concluded that the five strains have a highly close relationship in HA gene..In phylogenetic tree of H5 subtype AIV, the five mainland strains are clustered with HK/97 strains which indicates their close phylogenetic relationship.
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