Evaluation of N,N-diethyl-m-toluamide (DEET) as a topical agent for preventing skin penetration by cercariae of Schistosoma mansoni. Am J Trop Med Hyg 58: 828–834

Abstract. The effect of skin application of N,N-diethyl-m-toluamide (DEET) on the penetration and migration be-havior of cercariae of Schistosoma mansoni was evaluated in vitro and in vivo in a mouse model. These studies showed that DEET at concentrations of 7.5 % or higher was 100 % effective in immobilizing and killing cercariae of S. mansoni in vitro. Ultrastructural studies on such DEET-exposed cercariae showed transformative and degenerative changes in-volving both tegument and deeper parenchymal structures. Fatal tissue lesions were evident as early as 5 min postex-posure to DEET, and became more extensive with increasing exposure time. Cutaneous application of DEET (as a pure chemical in isopropanol or as a commercial insect repellent preparation) was more than 99 % effective in preventing entry of S. mansoni cercariae into the mouse tail skin. Radiolabeling and tracer studies confirmed that 7.5 % DEET applied to the skin prior to infection was highly effective in preventing schistosomular migration to the lungs. Despite the stringent control and prevention methods that are being practiced, schistosomiasis continues to be a life-threatening infection in many tropical and subtropical parts of the world.1 In addition, an increase in the international travel in recent years has predisposed many travelers visiting such endemic areas to a greater risk of acquiring the diseas