Miracidial host-finding in Fasciola hepatica and Trichobilharzia ocellata is stimulated by species-specific glycoconjugates released from the host snails.

The miracidia of Fasciola hepatica and Trichobilharzia ocellata approach their host snails Lymnaea truncatula and L. stagnalis by increasing their rate of change of direction (RCD) in increasing gradients of snail-conditioned water (SCW), and they perform a turnback swimming in decreasing gradients. Both hostfinding responses in both species were induced by glycoconjugates with a molecular weight of > 30 kDa that were sensitive to hydrolysis with pronase E and oxidation with NaIO4. Alkaline cleavage revealed that they contained carbohydrates linked O-glycosidically via serine and N-acetylgalactosamine. Miracidia clearly preferred SCW from their specific host snail versus other sympatric snail species and did not respond to water conditioned with fish, tadpoles, or leeches. Differences in the chemical characteristics of SCW from the intermediate hosts L. truncatula and L. stagnalis could be shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, blotting, and subsequent carbohydrate detection. The first step of purification of the effective signaling SCW components from both snail species was achieved by ion-exchange chromatography.