Detailed Explanation of the Pathological Lesions of Chicken Infectious Anemia

The most characteristic necropsy lesion of uncomplicated chicken infectious anemia is bone marrow atrophy. The bone marrow of the femur is fatty-colored, pale yellow, or pink; the thymus is atrophied and congested, and in severe cases may undergo complete involution. As the age of affected chickens increases, thymic atrophy is more readily observed than bone marrow lesions. Bursal atrophy is not obvious and is often transient; sometimes the weight is reduced and the volume is decreased, while in most affected chickens the bursa of Fabricius appears semi-transparent. In severely affected cases, the liver and kidneys may be seen to be enlarged, yellowed, and friable. Hemorrhage of the proventricular mucosa and subcutaneous and muscular hemorrhages are sometimes observed.

Histopathological examination reveals a reduction in erythrocytes, platelets, granulocytes, and their precursor cells in the bone marrow, which are replaced by adipose tissue. Thymic atrophy is the result of lymphocyte depletion in the cortex and medulla. Lymphocytes in the bursa of Fabricius and spleen are also reduced, but the degree and duration are less severe than in the thymus.