Lethal encephalitozoonosis in cyclophosphamide-treated rabbits

Encephalitozoonosis is an opportunistic infection in animals and humans. It s clinical form is observed in immunosuppressed hosts. We studied the occur rence of the manifest form of rabbit microsporidiosis under cyclophosphamid e immunomodulation in 40 New Zealand rabbits. The experimental animals were intraperitoneally infected with 5 x 10(7) Encephalitozoon cuniculi spores. Two weeks after infection the animals were treated intraperitoneally with cyclophosphamide, first with 50 mg/kg and then with 15 mg/kg weekly during the 12-week experimental period. Positive controls were either E. cuniculi- infected or cyclophosphamide-immunosuppressed animals. The negative control rabbits remained untreated. Both clinical signs of encephalitozoonosis and depression of peripheral blood cell count developed between weeks 4 and 6 in the experimental animals which died during week 6 of the experiment. No clinical signs compatible with encephalitozoonosis were observed in any of the controls. The results suggest that immunosuppression induced by cycloph osphamide can give rise to a lethal form of encephalitozoonosis.