Recrudescence of Anaplasma marginale induced by immunosuppression with cyclophosphamide.

Eight doses of cyclophosphamide (5 mg/kg), at 2-day intervals between doses, were administered IV to Anaplasma-carrier splenectomized calves. Significant decreases in serum immunoglobulins, diminished complement-fixing antibody response, and transitory leukopenia were associated with the treatment. Recrudescence of clinical Anaplasma infection occurred after the 5th dose of cyclophosphate was given and was characterized by rapid increase in parasitemia, marked decrease in PCV, and mortality. The results of the present study indicated that humoral mediated immunity may contribute to the maintenance of a state of equilibrium in the host-parasite relationship and that suppression of humoral immune responses may alter the course and outcome of infection in Anaplasma carriers.