Continuation of chloroquine-susceptible Plasmodium falciparum parasitemia in volunteers receiving chloroquine therapy.

Volunteers infected with a chloroquine-susceptible line of Plasmodium falciparum were administered standard oral chloroquine therapy at the first detection of parasites in the blood. Parasitemias progressed in the face of therapy for up to 5 days and to levels up to 100-fold greater than those at the initiation of treatment. Thereafter, infections cleared without a requirement for additional chemotherapy. This course of infection and response to treatment has not been previously reported and may have been detected because volunteers were exposed to an unusually large number of sporozoites. The observations are consistent with the hypothesis that prolonged parasitemia resulted from the continued release of merozoites from liver.