WR 238605, chloroquine, and their combinations as blood schizonticides against a chloroquine-resistant strain of Plasmodium vivax in Aotus monkeys.

The compound WR 238605 is a primaquine analog being developed by the U.S. Army as an antimalarial drug. Currently, there is no established treatment for Plasmodium vivax parasitemias that are not cured by chloroquine. This study tested WR 238605, chloroquine, and their combinations against a chloroquine-resistant strain of P. vivax (AMRU 1) in Aotus monkeys. A total dose of 3 mg/kg of WR 238605 given at a dosage of 1 mg/kg/day for three days cleared patent parasites in all eight monkeys but recrudescence of parasitemia occurred 15-25 days after initiation of treatment. A total dose of 9 mg/kg of WR 238605 over a three-day period cured all three monkeys of their infections. A total dose of 30 mg/kg of chloroquine did not clear patent infections in three monkeys, whereas a total dose of 60 mg/kg generally (two of three) cleared patent parasitemia but did not cure. Whereas total doses of 30 mg/kg of chloroquine or 3 mg/kg of WR 238605 given alone failed to cure, both drugs given in combination at these dosages cured two of three infections. These results indicate that WR 238605 may be an alternative treatment for chloroquine-resistant vivax malaria.

Susceptibility of Guyanan Saimiri monkeys to a chloroquine-sensitive and a chloroquine-resistant strain of Plasmodium vivax from Papua New Guinea.

Attempts were made to infect splenectomized Guyanan Saimiri sciureus monkeys with the following Papua New Guinean strains of Plasmodium vivax: AMRU-1, a chloroquine-resistant strain; and AMRU-2, a chloroquine-sensitive strain. Inoculation of 7 monkeys with the AMRU-1 strain, 4 using blood-stage parasites and 3 using sporozoites, all failed to produce infections. Inoculation of 4 monkeys with the AMRU-2 strain, 3 using blood-stage parasites and 1 using sporozoites, were all successful in establishing infections. The results suggest that Guyanan Saimiri are refractory to infection with the AMRU-1 strain. If refractoriness occurs in other species and subspecies of Saimiri monkeys, then studies on the AMRU-1 strain of P. vivax may be restricted to work using Aotus monkeys.