Evaluation of permethrin-treated military uniforms for personal protection against malaria in northeastern Thailand

Abstract

A trial to compare the effect of military clothing treated by high-pressure spray with permethrin or placebo on the incidence of malaria in Royal Thai Army troops was conducted in northeastern Thailand. Bioassays of treated clothing using laboratory-reared Anopheles dirus females showed permethrin remained in the treated fabric for up to 90 days. Both permethrin- and placebo-treated uniform shirts provided > 84% protection from biting An. dirus in laboratory bioassays for the duration of the study. In laboratory tests, knockdown of An. dirus exposed to permethrin-treated cloth fell to < 20% after 3 hand washes, despite the presence of 28.7-59.9% of the original dose of permethrin. The use of permethrin-treated uniforms without adjunct application of topical repellents did not reduce malaria in Thai troops in an operational setting where incidence during 6 months was as high as 412 cases/1,000 in spite of chemoprophylaxis and use of untreated bednets.