[Schistosoma, water and man]

The biology of schistosomes is increasingly better known due to the research works conducted since the early 1980s. Numerous data have been collected on: the structure of the genome; the genetic variability of natural populations; the causes of geographical distribution of Schistosoma species; the acquisition, probably recent, of the parasite as by modern man's ancestors; and even some aspects of development, such as the behaviour of larvae and the migrations in the circulatory system. Substantial advances have also been made in the maintenance of laboratory strains. Yet, multiple and fascinating problems are still raised by schistosomes. In the present state of our knowledge the origin and relationship of human parasitizing species are still hypothetical. Several features of reproduction, such as the existence of separate sexes and permanent couples cannot be explained. Quantitative data concerning the dynamics of transmission are much too vague to establish satisfactory mathematical models and to contribute usefully to strategies of control. Finally, the fact that schistosomes can develop either in man alone or in numerous mammals remain a mystery for immunologists and specialists of evolution.