SCHISTOSOMA-MANSONI - BIOMPHALARIA-GLABRATA - DYNAMICS OF THE SPOROCYST POPULATION IN RELATION TO THE MIRACIDIAL DOSE AND THE HOST SIZE

The rate of invasion of snails and percentage of the digestive gland o ccupied by daughter sporocysts decrease when the snails are larger and the miracidial dose is smaller. Growth of the sporocyst population is influenced not only by the miracidial dose, but also by the changes i n the growth rate of the host. The larger the host and (or) the smalle r the miracidial dose, the more significant is the volume occupied by the sporocyst population. Biomass- and (or) density-dependent regulato ry mechanisms of different patterns intervene to limit the volume of p arasites. Rapid colonisation and intensive exploitation of the host co rrespond to an immature plurimiracidial system, whereas progressive co lonisation and less exploitation correspond to a mature monomiracidial system. The results are discussed in terms of possible demographic st rategies that can be used to optimize parasite fitness in various envi ronments.