Schistosoma mansoni: cercaricidal effect of 2-tetradecenoic acid, a penetration stimulant.

Schistosoma mansoni cercariae are stimulated by 2-tetradecenoic acid (TDA) to penetrate agar substrates. TDA simultaneously causes tegumental transformation similar to that seen when cercariae transform to schistosomula, reduces the Cercarienhüllen reaction in immune human serum, and reduces larval tolerance to water. TDA damages cercariae that fail to penetrate or have no opportunity to do so. This damage apparently stems from increased tegumental permeability to water. Preincubation in TDA for 60 min reduces the percutaneous infectivity of cercariae to mice by from 95% at 0.2 ppm to 100% at 0.7 ppm TDA, but does not reduce the infectivity of subcutaneously injected cercariae. The interference with percutaneous infection seems to be entirely due to osmotic damage. TDA does not induce premature secretion of the acetabular glands or block host-recognition chemoreceptors. TDA may be a promising cercaricide for schistosomiasis control. It is highly specific for schistosome cercariae and is effective at low concentrations (0.2 to 0.7 ppm). Both cercariae and TDA tend to collect in the upper few millimeters of standing water. It is unlikely that cercariae can evolve resistance to a chemical that triggers the host penetration mechanisms.