Schistosomiasis mansoni: blockage of cercarial skin penetration by chemical agents: i. naphthoquinones and derivatives.

Skin penetration by Schistosoma mansoni cercariae may be blocked by 1,4-and 1,2-naphthoquinones applied topically. Of 23 naphthoquinone derivatives synthesized, 15 afforded almost complete protection when applied in solution to the tails of mice 24 hours before exposure to cercariae. On the basis of present evidence the 5-carbon atom side chain present in naturally occurring lapachol seems to be important for activity, and this is in accord with the previous observation that effective protective agents are liposoluble. Topically applied cercarial penetration inhibitors are presently the only prophylactic agents available for use in the field.