In vivo responses to antimalarials by Plasmodium falciparum and Plasmodiumvivax from isolated Gag Island off northwest Irian Jaya, Indonesia

There is renewed interest in the rich nickel and cobalt deposits of Pulau G ag, an isolated but malarious island off the northwest coast of Irian Jaya. In preparation for an expanded workforce, an environmental assessment of m alaria risk was made, focusing upon malaria prevalence in the small indigen ous population, and the in vivo sensitivity of Plasmodium falciparum and P. vivax to chloroquine (CQ) and sulfadoxine/pyrimethamine (S/P), the respect ive first- and second-line drugs for uncomplicated malaria in Indonesia. Du ring April-June 1997, mildly symptomatic or asymptomatic malaria infections were found in 24% of 456 native residents. Infections by P. falciparum acc ounted for 60% of the cases. Respective day 28 cure rates for CQ (10 mg bas e/kg on days 0 and 1; 5 mg/kg on day 2) in children and adults were 14% and 55% (P < 0.005). Type RII and RIII resistance characterized only 5% of the CQ failures. Re-treatment of 36 P. falciparum CQ treatment failures with S /P (25 mg/kg and 1.25 mg/kg, respectively) demonstrated rapid clearance and complete sensitivity during the 28-day follow-up period. More than 97% of the P. vivax malaria cases treated with CQ cleared parasitemia within 48 hr . Three cases of P. vivax malaria recurred between days 21 and 28, but agai nst low drug levels in the blood. The low frequency of RII and RIII P. falc iparum resistance to CQ, the complete sensitivity of this species to S/P, a nd the absence of CQ resistance by P. vivax are in contrast to in vivo and in vitro test results from sites on mainland Irian Jaya.