SCHISTOSOMA-HAEMATOBIUM CERCARIAL HOST-FINDING AND HOST-RECOGNITION DIFFERS FROM THAT OF SCHISTOSOMA-MANSONI

Schistosoma haematobium cercarial host-finding responses differ from t hose of Schistosoma mansoni. The attachment response to warm substrata is more sensitive and intense and is inhibited by unphysiologically w arm substrata. Attachment is also stimulated by L-arginine as the excl usive chemical cue of the human skin surface (threshold 3 mu M); howev er, the response is drastically lower than that of S. mansoni cercaria e. No chemical host stimulus could be identified for an enduring conta ct with the host after attachment. After attachment, the cercariae cre ep in a temperature gradient toward heat source; their response is, ho wever, more sensitive than that of S. mansoni (threshold 0.03 vs. 0.15 C/mm). Creeping S. haematobium cercariae orientate in chemical gradie nts in the same way as S. mansoni cercariae toward L-arginine as the e xclusive chemical signal of the human skin surface. The selective bene fit of this behavior is not yet understood. The penetration of both sp ecies is stimulated by free fatty acids from the human skin surface, n ot by heat. Thus, S. haematobium responds more to thermal host signals , whereas S. mansoni prefers chemical host signals.