Efficacy of permethrin-impregnated bed nets on malaria control in a hyperendemic area in Irian Jaya, Indonesia: influence of seasonal rainfall fluctuations.

A malaria intervention study was carried out using permethrin impregnated bed nets in the south-central part of Irian Jaya with perennial transmission, from April 1993 to April 1995. Malariometric surveys were carried out periodically for parasite prevalence by species and for spleen rates. Prior to intervention, the percentage of Plasmodium falciparum infected inhabitants was significantly higher in Hiripau, where permethrin-impregnated bed nets were used during the study, than in the placebo-treated control village, Kaugapu. After two years of intervention the situation was reversed and figures higher in the control village (RR 0.19, 95% CI 0.10-0.36, p < 0.0001). Similarly, P. vivax infection rates, 12.4% in Hiripau vs 5.7% in Kaugapu in April 1993. were reversed in April 1995 (3.6% in Hiripau and 11.3% in Kaugapu, p < 0.001). In the treated village, pre-control hyperendemicity was reduced to a low mesoendemic level (spleen rate 12.5%) during two years of intervention, whereas the level was mesoendemic (spleen rate 35.2%) in the control village. Impregnated bed nets were found an effective intervention both in moderate (April 1993 through April 1994, 1,626 mm rainfall) and high (April 1994 through April 1995/1995, 3,321 mm) transmission seasons.