Hematopathological changes in dead and moribund chicks induced by chicken anemia agent

Fifty day-old chicks were inoculated wit the Gifu-1 strain of chicken anemia agents. They began to show anemia and a drop in body weight 10 days postinoculation. Thirty-five of them died over a period of 12 to 23 days, mostly between 14 and 18 days postinoculation. Hematocrit value and red and white blood cell counts were markedly reduced in moribund birds. Polychromatic erythrocytes and granulocytes dropped in incidence in the peripheral blood accompanied with a fall in hematocrit value, and gained again with recovery from anemia. Macroscopically, dead and moribund birds revealed yellow bone marrow, marked atrophy of the thymus and bursa of Fabricius, discoloration and swelling of the liver, spleen and kidneys. In some cases, there were partially well-defined necrotic foci in the liver, round heart, fresh hemorrhages in the proventricular mucosa, erosion on the gizzard mucosa, and subcutaneous edema. Microscopically, marked hypoplasia or aplasia of hematopoietic cells in the bone marrow and severe depletion of lymphocytes in lymphoid organs, such as the thymus, bursa of Fabricius, spleen, and cecal tonsils, were commonly seen in affected birds. The changes described above suggested that the anemia induced by chicken anemia agent might closely be related to the bone marrow function.