To determine the relapse potential of a West African strain of Plasmodium ovale, we infected five volunteers (four Caucasians and one Negro) by bites of mosquitoes. Their initial and subsequent attacks were treated with 10 grains of quinine sulfate every 8 hours for 5 days, except one, who, because of his transfer to another institution, was given single doses of chloroquine, 600 mg (base). The period of observation ranged from 315 to 592 days. Each volunteer had at least one true relapse, three had two, and one had three. The shortest interval between the primary attack and the first relapse was 17 days and the longest interval was 255 days after treatment of the primary attack. The shortest interval between two relapses in any of the volunteers was 32 days and the longest was 142 days. These results leave little doubt that ovale malaria is a relapsing disease, but there appears to be no definite relapse pattern such as is recognized for the St. Elizabeth and Chesson strains of Plasmodium vivax.
Formerly Medical Officer in Charge, National Institutes of Health, Malaria Project, Laboratory of Parasite Chemotherapy, U. S. Penitentiary, Atlanta, Georgia. Present address: Chief, TMORU/PHUSOM, APO San Francisco 96346.
Formerly Chief, Laboratory of Parasite Chemotherapy, National Institutes of Health. Present address: 5012 Wickford Way, N.E., Atlanta, Georgia 30338.