Chronological observations on hemato-pathological changes in chicks inoculated with chicken anemia agent

Chicks were inoculated with the Gifu-1 strain of the chicken anemia agent (CAA) on the day of hatching. They manifested distinct anemia accompanied with pancytopenia 8--20 days after inoculation. Discoloration of the bone marrow and atrophy of the thymus began to be seen 6 days after inoculation. Histologically, hematopoietic cells began to decrease and large blastic cells to appear in the bone marrow 4--6 days after inoculation. Hypoplasia and subsequently aplasia occurred to all over the bone marrow 8 days after inoculation. In the bone marrow erythrocytopoiesis was noticed first 16--18 days after inoculation, granulocytopoiesis later, and transient hyperplasia finally. At last, the bone marrow returned to a normal condition 32 days after inoculation or later. In the thymus the depletion of cortical lymphocytes became distinct 4--6 days after inoculation, and lobular atrophy 8 days after inoculation or later. The depletion of lymphocytes in the other lymphatic tissues and hemorrhage in the lamina propria of the proventriculus were observed only in the anemic phase. The results mentioned above indicated that the anemia induced by CAA was caused by the disorder of hematopoietic cell formation in the bone marrow. It was also noteworthy that cortical lymphocytes in the thymus began to decrease remarkably soon after inoculation.