The Relationship Between The VP3,3'NCR Gene In A Segment And The Pathogenicity Of The VvIBDV GX8/99

Infectious bursal disease virus(IBDV),the causative agent of infectious bursal disease(IBD) , causes immunosuppression in young chickens by destroying the precursors of B lymphocytes in the bursa of Fabricius. In 1957, the disease first broke out in broilers in Gumboro, Telahua state, America. In the 1980s, the variation strain of IBDV was fiest appeared in America. Acute IBD caused by very virulent infectious bursal disease virus(vvIBDV) was first reported in Europe at the end of 1980s. The acute form of the disease were then transmitted to Japan in the early 1990s, and then rapidly spreaded all over Asia and other major parts of the world. The IBDV has beeen the cause of significant economic losses in poltry industry for a long time.We selected the GX8/99 strain ,we did research in the cycle of the initial bursal virus→cell-adapted virus→cell-clonedvirus→SPF-chicken-passage virus(from chickens).We also examined the evolution rules of pathogenicity and the relationship of the pathogenicity with nucleotide and amino acid. The research divide two parts:1.The sequence analysis of VP3 gene of the vvIBDV during the process of cell-cloned strains were passaged on chickensIn order to study the pathogenicity and the sequence analysis of VP3 gene of the very virulent infectious bursal disease virus (vvIBDV)。we extracted RNA from different passages of the initial bursal virus ,CEF cell-adapted virus ,cell-cloned virus,and SPF-chicken-passaged virus separately.After reverse transcription polymerase chain reaction(RT-PCR),gene cloning ,nucleotide sequence examination and analysis,we grasped the sequence of VP3 rengion during the passage process and deduced the evolutinon rules of amino acid sequence .Compared with the initial bursal ,4 sites of VP3 region from the CEF cell-adapted virus changed ,and these 4 sites are identical to that of the vaccine D78 virus strain. In the process of inoculation back the virus to chickens ,most of these 4 sites did not changed no longer. The 228th site changde from P of the initial bursal virus to L of the cell-adapted virus.But this site changed back to P when the virus was inoculated back to chickens at the 15th generation.The reults suggested that the varition of VP3 region perhaps assosciate with pathogenicity ,but had something to do with cell culture or tissue appetnecy.2.The sequence analysis of 3'-NCR gene in segment A of the vvIBDV during the process of cell-cloned strains were passaged on chickensIn order to study the pathogenicity and the sequence analysis of 3'-NCR gene ,in segment A,of the very virulent infection bursal disease virus(vvIBDV),we extracted RNA from different passage of the initial bursal virus ,CEF cell-adapted virus , cell-cloned virus,and SPF-chicken-passaged virus separately.After reverse transcription polymerase chain reaction (RT-PCR),gene cloning,nu- cleotide sequence of examination and analysis,we grasped the sequence of 3'-NCR region during the passage and deduced the evolution rules of amino acid sequence .Compared with the vvIBDV HK46,D6948 and GX ,the 20th amino acid of GX8/99 is proper and consistent with weak poison such as Cu-1M,P2,CEF94 , and there are no mutation in the process during the cell attenuation and chicken-passaging. Compared with the amino acid sequence of SPF-chicken-passaged virus B10,B15,B20, the initial bursal virus(GX8/99),cell-adapted virus 25(C25) and cell-cloned virus (CL) have no mutation.The research shows that 3'-non-coding-region gene ,in segment A ,of China IBDV strains have nothing with pathogenicity and cell culture or tissue appetency.