Comparative Biological And Molecular Biological Characters Of Chicken-origin And Duck-origin H₅N₁ Subtype Avian Influenza Viruses

In order to ascertain the different characters between chicken-origin and duck-origin H5N1 AIV, The pathogenity, antigencity, immunogencity,infectivity of the two viruses( KF and QS) were compared and analysised by ELD50 in the chicken and duck embryo, LD50 in the chicken and duck, IVPI in the SPF chicken and ducks,,cross-hemagglutinin inhibition test(HI),cross-virus neutralization test(VN) in the chicken and duck embryo and cross protection challege infection test. The result demonstrated ELD50 of KF in chicken embryo and duck embryo were 10-8.5/0.2ml and 10-8.44/0.2ml, which were bigger than QS `(10-7.5/0.2ml and 10-7.375/0.2ml). LD50 of KF in chicken and ducks were 10-8/0.2ml and 10-4.25/0.2ml ,which were also bigger than QS `(10-6.47/0.2ml and 10-2.63/0.2ml);likewise , IVPI of KF in chicken and ducks(2.77 and 2.66) is bigger than QS' (2.1 and 1.83). These finding revealed that the virulence of KF was stronger than QS`.The antigene relative modulu of HI and VN all were bigger than 0.67, which suggested the antigenticy of 2 strains was different. When challeged by KF or QS,those poultry inoculated with KF vaccine could be protected 80%-90% according to diffent host ,but inoculated with QS viccine could be protected only 75-80%, which suggest that the immunogencity of KF was better than QS'.The nucleotide sequence of complete cDNA of HA gene gained by gene clone and were sequenced, which included 1707 nucleotides and encoded for a protein of 568 amino acids , the amino acid sequences of the HA proteolytic cleavge site were –RDRRRKKR-, compatible with a high-pathogenic AIV.Sequence comparison of the two isolates showed 98.4%-99.4% nucleotide and amino acid sequence similarity. Nucleotide at the 906bp site of the HA gene of QS mutated into A, which caused the amino acid of potential glycosylation site to missing .Complete HA gene sequences of 2 strains were analyzed phylogenetically with 17 H5N1 subtype viruses available in the genebank database. It is concluded that 2 strains in our study may have the same origin with Thailand/04, but owned larger genetic distance with HK/156/97.The result of our study supported that the duck's ability to resistant to infection with the H5N1 virus was higher than chicken's; pathogenity and infectivity of duck-origin KF was stronger than chicken-origin QS ,and immunogencity of KF was better than QS', which provided scientific reference dates for prevention against H5N1 AIV and the selection of vaccine strains, especially in duck influenza.