The snail hosts of schistosomiasis: some evolutionary and ecological perspectives in relation to control

Despite opportunities for radiation provided by spatio-temporal isolation, the basic morphological plan of pulmonate snails has remained conservative. In consequence of the resulting dearth of morphological characters and their plasticity, there is a case for using biochemical characters such as exogenous chemicals released by the snails (e.g. amino acids) and their chemoreception niche as taxonomic aids to classify snails of medical importance. As these same chemicals are used by snails to distinguish conspecifics they could also be used as "environmental antibodies" in controlled release formulations (CRF's) designed to remove target snails in a specific, cost-effective and ecologically acceptable manner. The snails, surface-living bacteria, algae and macrophytic plants are considered as co-evolved, interactive modular systems with strong mutualistic elements. Recently, anthropogenic perturbations such as deforestation, and damming of flowing waters, have benefited these modules whereas others such as river canalization, acid deposition, accumulation of pesticide residues and eutrophication have harmed them. Research is needed to elucidate the factors which limit the growth of snails in primitive habitats, uninfluenced by man, as well as in those subject to harmful anthropogenic factors. The understanding thus gained could be applied to develop cost-effective primary health care strategies to reduce or prevent transmission of schistosomiasis and other water related diseases.

A schistosomiasis transmission model incorporating concomitant immunity

Este trabalho pretende ser uma contribuiçäo ao estudo dos mecanismos de regulamentaçäo da esquistossomose. Propöe-se uma modificaçäo nos modelos básicos desenvolvidos por McDonald e outros que leva em conta imunidade concomitante como mecanismo de regulaçäo. Portanto, enquanto em outros modelos básicos a regulaçäo se dava exclusivamente no hospedeiro intermediário o modelo aqui apresentado permite incluir a regulaçäo no hospideiro definitivo. Conclui-se que a regulaçäo no hospedeiro definitivo permite um ajuste muito melhor aos dados experimentais