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

There is renewed interest in the rich nickel and cobalt deposits of Pulau Gag, an isolated but malarious island off the northwest coast of Irian Jaya. In preparation for an expanded workforce, an environmental assessment of malaria risk was made, focusing upon malaria prevalence in the small indigenous population, and the in vivo sensitivity of Plasmodium falciparum and P. vivax to chloroquine (CQ) and sulfadoxine/pyrimethamine (S/P), the respective first- and second-line drugs for uncomplicated malaria in Indonesia. During April-June 1997, mildly symptomatic or asymptomatic malaria infections were found in 24% of 456 native residents. Infections by P. falciparum accounted for 60% of the cases. Respective day 28 cure rates for CQ (10 mg base/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 against low drug levels in the blood. The low frequency of RII and RIII P. falciparum resistance to CQ, the complete sensitivity of this species to S/P, and 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.

Comparative performance of the ParaSight F test for detection of Plasmodium falciparum in malaria-immune and nonimmune populations in Irian Jaya, Indonesia.

A comparison was made of the performance of the ParaSight F test (F test) for detection of Plasmodium falciparum in blood from malaria-immune (410 native Irianese) and nonimmune (369 new transmigrants) populations in Irian Jaya, Indonesia, where malaria is hyperendemic and all four species of human malaria occur. There were highly significant differences between populations in the sensitivity (Irianese, 60% versus transmigrants, 84%; P < 0.001) and specificity (Irianese, 97% versus transmigrants, 84%; P < 0.001) of the F test. The test had comparably high levels of sensitivity for Irianese children aged < or = 10 years, both age groups of transmigrants (76-85%), but low sensitivity for Irianese aged > 10 years (40%), among whom only 7% of parasitaemias < 120 per microliter and 69% of those > 120 per microliter were detected. Specificity was comparably high for transmigrant children aged < or = 10 years and both age groups of Irianese (93-98%). The low specificity for transmigrants aged > 10 years (79%) was due to a preponderance of false positives, frequently identified by microscopy as P. vivax. The results suggest that comparison based on microscopy underestimated the performance of the ParaSight F test and that malaria immune status, irrespective of P. falciparum density, may influence the test's sensitivity.

PIP: The ParaSight F test uses a nonmicroscopic dipstick approach to the rapid detection of Plasmodium falciparum in blood. The performance of this test was assessed in serum samples collected in Irian Jaya, Indonesia, from 410 native Irianese (malaria-immune) and 369 new transmigrants (nonimmune). Of particular interest was the capability of the F test to detect P. falciparum prevalence among children, whose immunity is less than that of adults. There were highly significant differences by population in the F test's sensitivity (60% for Irianese vs. 84% for transmigrants) and specificity (97% for Irianese vs. 84% for transmigrants). The test had high sensitivity levels (76-85%) for Irianese children 10 years of age and under and both child and adult transmigrants, but low sensitivity (40%) for Irianese over 10 years of age. Specificity was comparably high (93-98%) for transmigrant children and both age groups of Irianese. The low specificity (79%) for transmigrants over 10 years of age reflected a preponderance of false positives, frequently identified by microscopy as P. vivax. These findings suggest that microscopy comparisons underestimate the performance of the ParaSight F test and that malaria immune status, regardless of P. falciparum density, may influence the test's sensitivity.

Randomised placebo-controlled trial of primaquine for prophylaxis of falciparum and vivax malaria.

Drug resistance has made malaria prevention difficult and the new agents are too expensive for widespread use. Primaquine, an established drug for treatment, is potentially useful for prevention. Malaria prophylaxis with primaquine was evaluated in Irian Jaya during one year in Javanese men who were not deficient in glucose-6-phosphate dehydrogenase (G-6-PD). 126 volunteers were randomised to receive 0.5 mg/kg primaquine base or placebo daily (double-blinded), or 300 mg chloroquine base weekly (open). The protective efficacy of primaquine relative to placebo was 94.5% (95% confidence interval 57-99) for Plasmodium falciparum and 90.4% (95% CI 58-98) for P vivax. Attack rates for either parasite did not differ significantly between the chloroquine and placebo groups. Incidence density of physical complaints not associated with parasitaemia was low (17-18 complaints/person-year) and was about the same in all groups except for cough, which was increased in the primaquine group. Complete blood counts were normal and no evidence of hepatic or renal dysfunction was found with primaquine. However, at 50 weeks the primaquine group had a mean methaemoglobin of 5.8% (range 1.4-13%), which declined by half within 7 days of ending prophylaxis. When used daily for one year by men with normal G-6-PD activity, primaquine was well tolerated and effective for prevention of malaria.