SCHISTOSOMA-MANSONI AND SCHISTOSOMA-HAEMATOBIUM - MIRACIDIAL HOST-FINDING BEHAVIOR IS STIMULATED BY MACROMOLECULES

The miracidia of Schistosoma mansoni and S. haematobium approach their host snails by increasing their rate of change of direction (RCD) in increasing gradients of snail-conditioned water (SCW), and they perfor m a turnback response in decreasing gradients. After contact with the host ''repeated investigation'' is the typical host-specific response. Both species show no significant directed chemotactical orientation t owards their snail hosts. All three host-finding responses (increased RCD, turnback response, and ''repeated investigation'') seem to be sti mulated in both species by a similar component of SCW, a macromolecula r glycoconjugate with a molecular weight >30,000. The saccharide chain s seem to be O-glycosidically linked via serine and N-acetylgalactosam ine. The glycoconjugate is sensitive to lysozyme which may suggest tha t muramic acid as a gastropod-specific component is involved in the re cognition process. Small molecular components of SCW, as well as magne sium chloride offered as pure chemical, may cause a moderate increase in the RCD. Therefore a minor contribution of these components to the host-finding response of schistosome miracidia cannot be excluded. Tha t schistosome miracidia respond to complex macromolecules as host cues may indicate an adaptation to avoid interference of the host-finding with ubiquitous small molecular mud components and it might enable the miracidia to achieve a high degree of host-specificity in their host- finding.