Comparative Study On Pathogenic And Immunological Characteristics Of Various Virulent Strains Of Infectious Bursal Disease Virus

Using histopathological, electron microscopic, histo-chemical, immuno-histochemical, TUNEL, ELISA methods, Pathogenic and immunological characteristics of various virulent strains of infectious bursal disease virus (IBDV)-B87 strain(attenuted vaccine),BC6/85 strain (virulentIBDV,vIBDV),SNJ93 strain (very virulent IBDV,wIBDV) were observed. The results showed :1.SNJ93 strain caused serious damage not only in immunological organs but also in non-immunological organs. The pathological change of immunological organs of chickens infected with BC6/85 strain was less serious than those infected with SNJ93 strain, and only lesion of proventriculus and kidney were seen in non-immunological organs. B87 strain caused no lesion in immunological organs and non-immunological organs.2.After SPF chickens infected with BC6/85 and SNJ93 strains,the index of bursa was higher than that of the control group(p<0.05) on the third day post infection(PI), but significantly lower from the fifth to fourteenth day PI(p<0.01); The index of spleen was significantly higher than that of the control group from the third to fifth day PI(p<0.01); The index of thymus was significantly lower than that of the control group from the third to ninth day PI (p<0.01). The index of bursa had no significant difference between the B87 strain vaccinal group and control group(p>0.05). The index of spleen of B87 strain vaccinal group was higher than the control group(p<0.05) ,but lower than that of group infected with the SNJ93 or BC6/85 strain from the third to fifth day PI. The index of thymus of B87 strain vaccinal group was higher than that of groups infected with the BC6/85 or SNJ93 strain (p<0.05).3.ELISA method showed the antibody titers of groups infected with the BC6/85 or SNJ93 strain were higher than that of the control group from third to fourteenth day PI (p<0.01), and the former was lower than the latter(p<0.05). the antibody titers of B87 strain vaccinal group were greatly higher than that of the control group from the third to ninth day PI (p<0.01), and lower than groups infected with the BC6/85 or SNJ93 strain from third to seventh day PI (pO.Ol).4.The result of immuno-histochemistrical method showed: the number of CD4+and CD8+T cells of immunological organs in the experimental groups were more than that of the control group. The intensity and durative time of positive reaction were:SNJ93> BC6/85> B87. This positive reaction of CD8+ T cells was more obvious than CD4+ T cells in groups infected with the BC6/85 or SNJ93 strain.5.The result of H.E. and immuno-histochemistrial stain showed the number of IEL and positive slgA cells in duodenum, jejunum and cecal tonsil of B87 strain vaccinal group were more than those of the control group, but which of group infected with the BC6/85 or SNJ93 strain were less than that of the control group6. Substance P and vasoactive intestinal polypeptide (VIP) in duodenum had no difference between the B87 strain vaccinal group and the control group on the third day PI, but they were higher than the control group on the fifth day PI. Substance P and VIP were significantly higher than that of the controlgroup in jejunum, cecal tonsil, bursa and spleen from the third to fifth day PI . After SPF chickens infected with SNJ93 and BC6/85 third to fifth day PI, the substance P and VIP in duodenum, jejunum, cecal tonsil, spleen and thymus were significantly higher than the control group.7.Ultrastructurally, the numerous virus were observed in the cecal tonsil and kidney of groups infected with SNJ93 strain. And apoptotic bodies were observed in the lymhocytes of bursa. TUNEL method showed numerous apoptotic lymphocytes were seen in bursa of chickens infected with SNJ93 from first to seventh day, especially from the third to fifth day PI. Numerous apoptotic lymphocytes were seen in the group infected with BC6/85 strain only from the third to fifth day. But there were no difference between the B87 strain vaccinal group and the control group from first to ninth...