Identification of chemicals of snail origin that attract Schistosoma mansoni miracidia

Abstract

MEASURES to control schistosomiasis (bilharziasis) aimed at either the molluscan vector or the trematode's larval stages might be enhanced by a better understanding of the intricacies of how miracidia and cercariae find and penetrate hosts. Previous work from our laboratory identified chemicals from mammalian skin that initiated penetration responses by Schistosoma mansoni cercariae¹. Other earlier studies implicated amino acids and additional compounds as attractants of S. mansoni miracidia to the molluscan host, but did not show that these substances were derived from the snail². Subsequently, based on Neuhaus'³ and C. A. Wright's⁴ indications that snails release substances into water that stimulate miracidia, several investigators^5–8 have confirmed that snails ‘condition’ water making it stimulatory or attractive to miracidia. Wright and Ronald⁹ recently demonstrated that water conditioned by the snail Lymnaea palustris attracted miracidia of the rodent blood fluke, Schistosomatium douthitti, and that this snail-conditioned water (SCW) contained amino acids. Here we show that Biomphalaria glabrata, the molluscan vector of S. mansoni, the important parasite of humans, contributes amino acids to the aqueous environment, and that these, and possibly other substances elicit chemotactic and chemokinetic responses by miracidia of this parasite.