Two strains of Plasmodium malariae, one from the Philippines and the other from Nigeria, were studied in 23 volunteers. In infections induced by the intravenous inoculation of parasitized blood, the peak parasitemias of from 1,400 to 27,000 per mm3 were attained on from the 13th to the 28th days of patent parasitemia. The median day of maximum parasitemia was 16 days. Neither strain in man readily infected mosquitoes. Transmission was obtained to six volunteers via the bites of Anopheles freeborni mosquitoes infected by feeding on owl monkeys. The prepatent periods ranged from 24 to 33 days with a mean of 27.5 days. Both strains of malaria were cured by treatment with 600 mg (base) chloroquine. Treatment of the Philippine strain with quinine sulfate (30 grains per day for 5 days) was also curative. The failure of the sporozoite induced infections to relapse after treatment with blood schizontocides suggests that P. malariae does not possess a fixed-tissue relapse mechanism.
Center for Disease Control, Malaria Program. 1600 Clifton Road, Atlanta, Georgia 30333.