Studies On The Attenuation Of VvIBDV Gx Strain

This research is an important part of INCO-DC Project (ERBIC18CT980330) named "Acute Infectious Bursal Disease in Poultry: Epidemiology of the Disease, Basis of Virulence and Improvement of Vaccination ".One strain wIBDV was isolated and identified from china according with European and O IE standard .This part research aims at seeking the virulence marker of very virulent infectious bursal disease virus(wIBDV) in molecule level through the attenuation study.VvIBDV Gx strain with high pathogenicity was attenuated through replicating in SPF embryo and CEF successfully. The change pattern of VP2 nucleotide and the deduced amino acid sequences were obtained from this strain of wIBDV to attenuated one during the process of attenuation. The results of sequencing , analyzing of every generation viruses showed that there was not any changes on VP2 gene before CEF-7 generation, there was a few changes in VP2 gene but not on amino acid at CEF-8 generation , the homology of amino acid sequence with European reference wIBDV strain was up to 100%; The virus of CEF-9 generation was an intermediate with complex changes. CEF-10 generation had become cell-adapted strain, the homology of amino acid sequence with European reference IBDV attenuated strain Cu-1 was up to 97%. VP2 gene did not changed any more from CEF-10 to CEF-20 generation. The results of pathogenicity tests showed that the original (Gx) was typicalvvIBDV with the mortality up to 64%, the virus of CEF-5 generation was still wIBDV with the mortality up to 60% in 4-week-old SPF chickens, while the virus of CEF-15,CEF-20 generation was not pathogenic and CEF-20could not atavistic after propagated 6 generation in SPF chickens.We do more research on CEF-9. The results of researching on its molecular biology and biological characterizations shows that: the VP2 gene of CEF-9 has some characters of wIBDV strain as well as some characters of attenuated strain, pathogenicity of CEF-9 is between wIBDV strain and attenuated strain; and CEF-9 is not stable due to the fact that i t could be attenuated in vitro and could rapidly atavistic in vivo. All the results demonstrate that CEF-9 is an intermediate form from high virulence to low virulence during the attenuation. All the results shows that wIBDV gene is liable to change through this attenuated way and wIBDV could change into an intermediate and an attenuated strain.This has maken substance and theory foundation for the further research on the virulence of IBDV.Candidate: Zeng Xiang wei Major: Preventive Veterinary ScienceSupervisor: Prof. Wei Ping Prof. Wang Xiao mei...