The potential use of N,N-diethyl-m-toluamide (DEET) as a prophylactic agent in the control of schistosomiasis.

DEET (N, N-diethyl-m-toluamide) is one of the reliable and most widely used insect repellents. This work was planned to study the effect of DEET on Schistosoma mansoni cercariae viability (in vitro) and skin penetration and migration (in vivo). DEET concentrations of 30%, 15% and 7.5% were highly efficient in killing all cercariae in vitro within 30, 60 and 240 minutes respectively. Two concentrations of DEET (15%) and (7.5%) were tested separately for their antipenetrant and protective effects in mice by immersing their tails in the drug and then exposed to cercariae, 30 minutes later. DEET antischistosomal activity was assessed by the number of non penetrating cercariae, worm burden, egg count/gram liver and number of liver granulomata. The maximum prophylactic effect was recorded using DEET (15%) where the percentage of resistance reached 100% compared to 92% using DEET (7.5%). DEET was highly effective in preventing penetration of cercariae as well as its further migration to liver which is proved histopathologically in the liver. The persistence of the antipenetrant and protective effects of DEET over several days post application and following different water wash durations was examined. Treatment of mice tails with DEET (15%) and (7.5%), three days prior to infection, showed significant levels of resistance of 94.8% and 82.7% respectively. DEET (15%) provided 100% and 97.9% resistance even when treated tails were washed for 1 and 2 hours respectively.