Clinical and laboratory characterization of a chloroquine-resistant Plasmodium falciparum strain acquired in the Central African Republic

This case of chloroquine prophylaxis failure occurred in the Central African Republic, a country heretofore unaffected by chloroquine resistance. The clinical findings and chloroquine blood levels and blood smears confirmed prophylaxis failure. In vitro susceptibility testing demonstrated the parasite to be 3- to 4-fold more resistant than a susceptible reference clone.

An ultrastructural study of the effects of mefloquine on malaria parasites

The ultrastructural changes induced by the administration of a recently developed antimalarial drug, mefloquine, were studied in mice infected with Plasmodium berghei and human erythrocytes infected with P. falciparum in vitro. Pronounced changes which occurred in both experiments comprised swelling of the parasites' food vacuoles with gradual loss of pigment granules, which did not form clumps as occurs with chloroquine. These findings suggest that the malarial parasites' food vacuole is the target of this drug.

Adaptation of the Indochina I/CDC strain of Plasmodium falciparum to the squirrel monkey (Saimiri sciureus)

The Indochina I/CDC strain of Plasmodium falciparum was linearly passaged in squirrel monkeys (Saimiri sciureus) of 3 phenotypes. Splenectomized monkeys of Guyanan and Peruvian type developed high density parasitemias, but considerably lower than the mean peak parasitemia (greater than 10(6)/mm3) in Bolivian phenotype squirrel monkeys. Spleen-intact Bolivian and Peruvian squirrel monkeys all developed potentially lethal infections after linear passage of parasites from Saimiri and Aotus. For the evaluation of induced immunity to P. falciparum, the Indochina I/CDC strain in Saimiri will be a valuable model system.

In vitro activities of and mechanisms of resistance to antifol antimalarial drugs

Certain drugs that interfere with folate metabolism (sulfones, sulfonamides, and inhibitors of dihydrofolate reductase) play an important role in the chemotherapy and prophylaxis of malaria. The activities and mechanisms of action of these drugs are regarded as similar in most respects to their activities against procaryotic microorganisms. Believed incapable of utilizing intact exogenous folates, plasmodia have been regarded as dependent on de novo synthesis of required folate cofactors. The present investigation, conducted in pursuit of a method for testing the in vitro susceptibility of Plasmodium falciparum to antifol antimalarial drugs, produced evidence that earlier assumptions about the folate metabolism of this organism are not correct. Three of four isolates of P. falciparum were successfully maintained in a culture medium depleted of folic acid and p-aminobenzoic acid. The antimalarial activities of sulfonamides and dihydrofolate reductase inhibitors were, furthermore, variably antagonized by the presence of folic acid and p-aminobenzoic acid in the culture medium. Optimum conditions for assessment of antifol antimalarial activity in vitro therefore require precise control of these factors in the culture medium. Our results suggest that resistance to antifol antimalarial drugs involves a complex of factors related to both the de novo synthesis of active folate cofactors and the ability to utilize exogenous intact folates in various forms.