Cyclic hematopoiesis associated with feline leukemia virus infection in two cats.

Cyclic oscillations in the numbers of blood elements were detected in 2 cats with FeLV infection. Periodic neutropenia, followed by a return to normal neutrophil numbers, was detected in both cats. The mean cycle duration was 11.8 days, with a range of 8 to 14 days. Just before the return of normal neutrophil numbers, monocytosis developed. In 1 cat, cyclic variations in the number of reticulocytes and platelets also were detected. Bone marrow aspirates obtained during periods of neutropenia had a predominance of progranulocytes in the myeloid cell line. myeloid hyperplasia, with numerous segmented neutrophils, was seen in bone marrow aspirates obtained during periods of normal neutrophil numbers. Oral administration of prednisolone resulted in cessation of the cyclic oscillations of blood elements in 1 cat. Cyclic hematopoiesis appeared to be another non-neoplastic manifestation of FeLV infection.