Babesiosis in Long Island. Host-parasite relationships of rodent- and human-derived Babesia microti isolates in hamsters.

The effects of splenectomy and size of inoculum on response of hamsters to three isolates of Babesia microti (two rodent- and one human-derived) from Long Island were studied. Splenectomy of hamsters did not enhance susceptibility to the rodent isolates of B. microti at a dosage of 5 X 10(7) parasites. Larger parasite inocula produced shorter prepatent periods and slightly shorter duration of infection in intact hamsters. Inoculum size was not contributory to mortality of hamsters or to pathogenesis. Hamsters showed profound anemia with depressed hematocrit and hemoglobin values and erythrocyte counts. Moderate leucocytosis was seen just prior to peak parasitemia, with immature polymorphonuclear cells predominating. Infections in hamsters lasted for 14--17 weeks. As determined by the parameters studied, the three isolates appear to be identical.