Efficacy of permethrin-impregnated bed nets on malaria control in a hyperendemic area in Irian Jaya, Indonesia: differentiation between two age groups.

A malaria intervention trial was conducted for two years to evaluate the efficacy of permethrin-impregnated bed nets in reducing malaria infection and splenomegaly in two different age groups, ie below and over age of ten, in a hyperendemic area in Irian Jaya, Indonesia. Permethrin-impregnated or placebo-treated bed nets were provided to a treated and a control village, respectively. Immediately after periods with moderate rainfall in the first year, treated bed nets decreased P. falciparum and P. vivax density in the blood of children <10 years (group 1) but did not reduce the percentage of infection with either species. Children >10 and adults (group 2) showed significant reduction only in P. falciparum infection rates and density, whereas P. vivax was not influenced. After an excessive rainfall season in the second year, the risk for P. falciparum infections in both age groups using treated nets was less than half of that in the control village. P. vivax infection rates were significantly lower in the treated village at the beginning of and after these heavy rainfalls. In the treated village, spleen enlargement was markedly reduced in the younger age group during the second year.