Schistosoma mansoni:interference with cercarial host-finding by various aquatic organisms

Abstract

ABSTRACTSchistosoma mansonicercariae labelled with75Se-methionine were used to study host-finding capacity by determining the radioactivity of exposed mouse “target” tails. Possible interfering effects of some aquatic vertebrates and invertebrates, plants and algae and secretions and excretions of aquatic organisms were examined.A marked interferent effect due to predatory behaviour was produced byCyclops strenuus(Copepoda),Daphnia pulexandD. longispina(Cladocera),Notodromas monachaandCypria ophthalmica(Ostracoda) andLebistes reticulatus(guppy).Bufo bufo(Amphibia) andPlanaria lugubris(Turbellaria) interfered significantly, presumably by secreting cercaricidal toxins. Several other organisms apparently produced no interference. The interferent effect of the plant speciesCeratophyllum demersum, Elodea canadensis, Lemna minor, Ranunculus aquaticus, Holcus lanatus(grass) andBotryococcus brauniiwas particularly pronounced when they were confined to the surface layer of the water. Several other species did not interfere with host-finding.