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Three standard antimalarial compounds were tested against trophozoite or sporozoite induced infections of the Panamanian Achiote strain of Plasmodium vivax in two species of monkeys. In Saimiri sciureus (24 subjects) and Aotus trivirgatus (11 subjects), parasite clearance from the peripheral blood averaged 3 days after initiating chloroquine therapy (total dose of 25 mg base/kg body weight over 3 days or single dose of 10 mg base/kg. Trophozoite induced infections were cured in all of 10 Saimiri and all of 6 Aotus, as indicated by the absence of relapses. Relapses did occur in 3 of 11 tests with Saimiri and 3 of 5 tests with Aotus against sporozoite induced infections. Subpatent periods ranged from 38 to 111 days among intact and splenectomized hosts. This is the first chemotherapeutic evidence for the persistence of exoerythrocytic stages of P. vivax in New World monkeys. Pyrimethaminr (single dose of 1 mg/kg) cured trophozoite induced infections in all of five Saimiri hosts. Radical cure of sporozoite induced infections was accomplished in each of six trials with chloroquine (25 mg base/kg) plus primaquine (1 mg base/kg for 14 days). The primary attack or relapse was treated. These models warrant further investigation in chemotherapy.

The authors present the results of a study carried out to determine the efficacy of chloroquine- and pyrimethamine-salt mixtures as a suppressive against sporozoite-induced vivax malaria (Chesson strain). The test subjects used in this study were volunteers of military age in the US Penitentiary at Atlanta, Ga. The subjects chosen were all in good physical condition and had no previous history of malaria.Both drug-salt mixtures were entirely acceptable to the volunteers, were indistinguishable in taste and appearance from ordinary salt, and remained stable under the conditions of food preparation. The weekly dosage of the drugs (300 mg of chloroquine base or 25 mg of pyrimethamine per 50 g of salt) had in each case been adjusted to the average salt consumption. Suppression of malaria was found to be complete throughout the salt-drug regimen and for 28-43 days thereafter, even though the subjects were exposed to repeated heavy doses of sporozoites. In contrast, the control subjects, exposed to the same infective doses, all exhibited parasitaemia 13-15 days after exposure.The procedures for preparing the drug-salt mixtures are described in detail and a simple method for determining the salt consumption by measurement of the urinary chloride excretion is outlined.