Study On The Evolution Rules Of Pathogenicity Of VvIBDV During The Coures Of Subculturing

The GX8/99 strain of vvIBDV was elected.Its virulence is highest and the mortality is 90%.After the passage of the GX8/99 virus strain,we did research in the cycle of the initial bursa virus(from chicken)→chicken-embroy-passage virus →cell-cloned virus→SPF-chicken-passage virus(from chiken).We examined the evolution rule of pathogenicity.Primary study showed that the pathogenicity of the initial bursal virus was the strongest,then were chicken-embroy-passage virus,while the cell-cloned virus were the weakest.When the cell-cloned virus were returned to chicken of SPF,the pathogenicity increased gradually.Apoptosis of lymphocytes in bursa was detected by light microscope and electron microscope .The results showed that apoptosis of lymphocytes in bursa was detected at early phase in all grope infected by IBDV.But the degree of apoptosis was different in some gropes.The chicken infected with initial bursal virus were the heaviest but the lightest in the grope infected with cell-cloned virus.The result of electron microscope showed that the content of viru in lymphocytes in bursa was different.Virus in some gropes were sporadic but in other gropes were many occluded virus.Dynamic changes of histopathology were studied on immune organs and some visceral organs .The results showed lymphoid follicles in bursal baemorrhage and atrophy. Lots of lymphocytes necrosis.Many neutrophilic granulocytes appeared in the interstitium of lymphoid follicles during anaphase of infection. The aparameter of bursal became smaller after infection.But there was no distinct relation between the degree of depletion with pathogenicity. IBDVs of different virulence all could induce thymus atrophy.The quantity of lymphocytes in the thymic cortex decreased differently in different gropes.There were many place in which lymphocytes deleted. The index of thymus also become smaller after infection. The degree of depletion was correlated with virulence. There were also lesion in spleen and cecal tonsil. The quality of lesion was elementarily same,but the degree was mostly different.The lesion was the most seriously in chicken infected with initial bursa viru while cell-cloned virus was the lightest. In others visceral organs,different degree of inflammatory response appeared. Lymphatic tissue in them necrosed.It was the most seriously in the grope infected with initial bursa virus. The result of ANAE stain showed lymphocytes which ANAE reaction was positive not only distribute beside center artery and a little of them but also distribute in splenic nodules and ellipsoids.Compared with control the quantity of this kind lymphocytes decreased in chicken infected with IBDV.From the quantity of the lymphocytes a conclusion could be drawn.The quantity of lymphocytes which ANAE reaction changed accompanying with the virulence of IBDV.IBDV can make immune organs lesioned thus the differentiation of T lymphocytes was affected.So the quantity of the lymphocytes deleted.