Study Of The Biological Characteristics Of Infectious Bursal Disease Virus Median Virulent Strain (IBDV-HZV)

Infectious bursal disease (IBD), the caused by infectious bursal disease virus (IBDV), is one of main infectious disease in the world. In recent years, antigenic variant IBDV strains and very virulent IBDV strains (vvIBDV) have been emerging and caused considerable economic losses to the poultry industry around the world. The traditional inactivated or attenuated vaccines could not provide enough protection against these variants and vvIBDV. Therefore, a new generation of more effective and safer vaccines is anticipated. The purpose of this study was to develop a new median virulent strain IBDV-HZV what was isolated from Fabricius pouch of the sick chicken flocks through domesticated of chicken embryos to effectively control of IBD.In this study, Physicochemical affection of IBDV-HZV strain was mensurated. The results shows, IBDV-HZV strain ELD₅₀ has not remarkable changed after deal with 60rain in pH2, but it has remarkable changed after deal with 60min in pH12, IBDV-HZV strain has characteristics of strong resist acid and weak resist alkali, it also has strong resist heated characteristic, its ELD₅₀ has not remarkable changed after deal with 30min in 60℃. IBDV-HZV strain has strong resist organic reagent characteristics and can not agglomerated chicken erythrocyte that substantiated it has not virus envelope.In this study, some SPF chicks were used for security test, immunosuppression test, immunity effectiveness test and movement disciplinarian of antibody after inoculated of IBDV living vaccine. IBDV-B87 was a contrast strain. The results shows, security, immunity effectiveness and movement disciplinarian of antibody of IBDV-HZV strain were better than IBDV-B87 strain. In addition, IBDV-HZV Strain can immunised for chickens through cohabitation infection and IBDV-HZV Strain can not causes immunosuppression in young chickens. So IBDV-HZV Strain a good spare vaccine strain.In this study, The Trizol agentia used to acquired gene of IBDV from SPF chicks Fabricius pouch that inoculated IBDV-HZV strain. According to the published sequence of IBDV strains, a pair of primers that can amplify the cDNA of protective antigen VP2 gene was designed and synthesized. By RT-PCR, a single DNA fragment of about 1.5kb was obtained from IBDV-HZV strain. Then the VP2 cDNA was cloned into pUC19 vector at EcoRI and XbaI sites. The nucleotide sequence of the expected VP2 gene was determined from pUC19-VP2. It showed that sequence comparison of IBDV-HZV with vvIBDV, the homology of amino acid was 99.6%, the homology of nucleotide sequence was 99.4%, IBDV-HZV strain has all specific amino acid of vvIBDV and the heptapeptide and the hydrophic peaks were uniform with vvIBDV, but IBDV-HZV strain has 279N and 284T specific amino acid, Therefore, IBDV-HZV strain was mutagenesis from vvIBDV, these specific amino acid explained characteristics of IBDV-HZV strain can not multiplication from CEF and virulence weakened, because mutation of specific amino acid of IBDV-HZV strain result in virulence weakened but has the better immune effectiveness for chickens. The study for specific amino acid not only can authenticate excellent characteristics of IBDV-HZV strain but also afford reference for choice spare vaccine strain.