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 approa ch their host snails Lymnaea truncatula and L. stagnalis by increasing their rate of change of direction (RCD) in increasing gradients of sn ail-conditioned water (SCW), and they perform a turnback swimming in d ecreasing gradients. Both host-finding responses in both species were induced by glycoconjugates with a molecular weight of > 30 kDa that we re sensitive to hydrolysis with pronase E and oxidation with NalO(4). 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 s nail species and did not respond to water conditioned with fish, tadpo les, or leeches. Differences in the chemical characteristics of SCW fr om the intermediate hosts L. truncatula and L. stagnalis could be show n by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, blotti ng. and subsequent carbohydrate detection. The first step of purificat ion of the effective signaling SCW components from both snail species was achieved by ion-exchange chromatography.