Selection And Cultivation Of The Cell-cloned Virus Strains Of VvIBDV And Their Influence To Immune Organs

Infectious bursal disease(IBD) is a highly contagious infection of chicks characterized of immuno-suppression ,and the primary means to control it is to use vaccines. In the late of 1980s, vaccination failure often happened because of the appearance of vvIBDV and the variant strain of IBDV. In order to develop high efficient vaccines,many scholars succeeded in cultivation of the vvIBDV strain and the attenuated variant strain .Rosenberger was the first person to attenuate the variant strain E of IBDV in the chicken embryo fibroblast (CEF) .Kibenge acquired the attenuated strain A by Vero cell. Tsai cultivated variant strains IN and E in BGM-70 separately with the result of pathogenicity loss. This experimentation use the strain GX8/99 of vvIBDV isolated in our country as the research object, passage the virus in embryonating eggs for 10 generations ,then blind passage it in CEF for 22 generations and the virus begin to adapte to CEF and cause cytopathogenic effect (CPE), with the cell gathered ,draw to fibril ,then change to round and shed off finally. Cloning the 25th generation of virus two times by infinite dilution method can get 4 cloned virus strains after sieving. Identify the intial bursal virus,embryo-passagevirus and cell-cloned virus separately by the methods of AGP,Strip and fluorescence antibody . Examine the 50％ embryo lethal dose (ELD50) of the strain GX8/99 and the cell-cloned virus separately, and examine the mean tissue culture infective dose (TCID50 ) of the cell-cloned virus . with the results that the titration of the intial bursal virus in embryos is the most high,that of the cell-cloned virus are slightly lower.And the four cell-cloned virus have different affinity to embryos and CEF.We can confer that the four cell-cloned virus are not the same one. Use methods of strip,AGP and fluorescence antibody to examine the virus in the initial bursal virus strain,embryo-passage virus strains and the cell-cloned virus strains,the results demonstrate the existion of IBDV,In these three kinds of examinations methods, with trip method is the most simple, convenience, quickly, and the intelligent degree is very high too.( can attain 10-4 ～ 10-5)Inoculate 4-week-old SPF chickens respectively with the initial bursal virus and four cell-cloned virus ,compared with the health chickens, the immune index of these chickens are all low 1.72 ～ 3.06 times, the thymus index are all low,and the initial bursal virus are the most serious, lower 4.54 times than control, the cell-cloned are slightly light, lower 1.26 ～ 1.79 times than control;The spleen index are all 1.14 ～ 1.64 times high than control , in a word ,the initial virus and the cell-cloned virus all can cause bursal and thymus atrophy, the spleen swells, primary announced the mechanism of immunosuppression caused by very virulent IBDVWe get four cell-cloned virus by passage the GX8/99 strain of vvIBDV in embryos and CEF .Inoculate the chickens of SPF with the result that the mortality lower than 6.7%, and that of the cell-cloned virus strain 1 and 4 are zero. We can foresee that the attenuated vaccination strain can be aquired by this way,this can establish the basis for prevention from the infection of vvIBDV.