Continuous in vitro propagation and differentiation of cultures of the intramolluscan stages of the human parasite Schistosoma mansoni

The metazoan parasitic blood flukes, Schistosoma spp,, infect over 200 mill ion people worldwide and cause extensive human morbidity and mortality. Res earch strategies for development of anti-schistosomal agents are impeded by the organism's complex molluscan-mammalian life cycle, which limits experi mental approaches and availability of material. We derived long-term contin uously proliferative cultures of Schistosoma mansoni sporocysts capable of generating cercariae in vitro. Cultured organisms retained the ability to p arasitize the host, and they exhibited developmental regulation of candidat e stage-specific genes in the host-free culture system. Evidence for expres sion of a reverse transcriptase also was found in the cultured organisms, p ointing to this activity as a possible mechanistic contributor to the dynam ic relationship between the parasite and its hosts. Continuous in vitro pro pagation of the asexual sporocyst stage allows isolation of clonally derive d parasite populations and provides a means to study schistosomal molecular genetics, metabolism, and evasion of host defenses.