Schistosoma mansoni and S. haematobium: Miracidial host-finding behaviour is stimulated by macromolecules

Abstract

The miracidia of Schistosoma mansoni and S. haematobium approach their host snails by increasing their rate of change of direction (RCD) in increasing gradieuts of snail-conditioned water (SCW), and they perform a turuback response. Both species show no significant directed chemotactical orientation towards their snail hosts. All three host-finding respeases (increased RCD, turnback response, and “repeated investigation”) seem to be stimulated in both species by a similar component of SCW, a macromolecular glycoconjugate with a molecular weight >30,000. The saccharide chains seem to be O-glycosidically linked via serine and N-acetylgalactosamine. The glycoconjugate is sensitive to lysozyme which may suggest that muramic acid as a gastroped-specific composent is involved in the recognition process. Small molecular components of SCW, as well as maguesium 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. That schistosome miracidin 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