Basic Biology and Tropistic Behavior of Schistosoma Mansoni Cercarta Relating to Cercaricidal Agents and Cercarial Repellents

摘要

In the search for plant oils as protective agents against the infection of mice by Schistosoma mansoni cercariae, two additional oils (Fennel and Vetiver oils) were found highly effective (Pterodon oil had already been reported as active). The cheek pouch of the hamster is being used for in vivo studies of the mechanisms involved in the protection afforded by these active oils. No protection has been conferred by cedrene and caryophylene - the chief known constituents of Pterodon oil - to mice against the infection by S. mansoni cercariae. Fractionating studies of Pterodon oil are in progress. Remarkable cercaricidal activity is displayed by Pterodon oil. Cedrene slightly affects S. mansoni cercariae and caryophylene was found to be inactive. Pterodon oil does not possess any systemic activity on mature schistosome infections in mice. Three proteolytic components were obtained by column chromatography from S. mansoni cercarial extracts. The major proteolytic fraction shows a chymotryptic like specificity on synthetic substrates. Inhibitors of alpha chymotrypsin also inhibit the cercarial enzyme. The cutaneous response to the purified cercarial enzyme complex is being investigated. Laboratory and field experiments demonstrated that the guppy (Lebistes reticulatus) is an active predator of S. mansoni cercariae and that under special conditions it represents an important limiting factor to the infection of vertebrate hosts. It was shown that most of molluscicides in current use are remarkably toxic for the guppy. Some problems related to the biological control of schistosomiasis snail vectors are discussed. (Author)