Effect of topical agents on cercariae of schistosoma mansoni

The present work was planed to evaluate the effect of free N, N- diethyl-m- toluamide [DEET], controlled release DEET and white precipitate ointment on the viability of cercariae of S. mansoni in vitro. They were also topically applied to mice to study their efficiency in preventing cercarial skin penetration. Free DEET and controlled release DEET formula caused immobilization and death of cercariae within 20 and 5 min, respectively. The number of adults detected after the application of free DEET and white precipitate ointment to mice skin prior to infection were significantly lower than the control group. When controlled release DEET was applied, no adults could be detected, indicating the failure of cercariae to enter through the skin. This was confirmed by histopathological study of the liver which was free of granuloma. Scanning electron microscopy revealed tegumental changes in cercariae exposed to both free DEET and controlled released DEET. So, topical application of any of the three chemicals was found to be effective in controlling S. mansoni infection. The best was with controlled release DEET