Finding and recognition of the bovine host by the cercariae of Schistosoma spindale.

The cercaria of Schistosoma spindale finds and identifies its bovine host with at least five behavioral phases. (1) Dispersal in and selection of midwater and water surface as the microhabitat are achieved by an intermittent swimming behavior with a weak geonegative but not photopositive orientation. (2) Attachments are stimulated by host-specific higher temperatures of the substrate but not by chemical host signals. (3) Remaining of the attached cercariae on the substrate is stimulated by host-specific higher temperatures of the substrate; chemical host signals have no effect. (4) The creeping of the cercariae is directed to the higher temperature in thermal gradients as weak as 0.07 degrees C/mm. Chemical gradients had no effect on the creeping direction. This behavior may enable the cercariae to migrate along hairs to the host's skin surface. (5) Penetrations are stimulated by the free fatty acid fraction of bovine skin-surface lipids. The characteristics of the stimulating fatty acids are the same as those identified for other schistosome species. Higher temperatures of the substrate alone do not stimulate penetrations. S. spindale cercariae do not use as many chemical host cues as stimuli for the identification of their host as do S. mansoni cercariae. S. spindale seems to be adapted to hairy hosts that are infected in shallow, muddy waters. The low host specificity of the cercarial host-finding behavior is compensated by an intimate parasite-snail intermediate host relationship, resulting in a high cercarial production of up to greater than 7,000 cercariae per snail per day.