Flukes without snails: advances in the in vitro cultivation of intramolluscan stages of trematodes.

In vitro cultivation of parasitic helminths, including the digenetic trematodes, has long been a valuable tool in medical and veterinary parasitology, permitting and/or facilitating the development of diagnostic reagents, chemotherapeutic agents, and vaccines and providing insights into naturally complex host-parasite interactions. In vitro cultivation of the intramolluscan stages of trematodes has been particularly challenging, given the ontogenic complexities involved in the production of multiple larval generations from germinal tissues through an asexual "budding" process. Recently, however, advanced larval development has been achieved by incorporating the Biomphalaria glabrata embryonic (Bge) cell line into cocultivation systems. Most notably, the entire intramolluscan cycle (from miracidium to cercaria) has been completed for the human blood fluke Schistosoma mansoni, while significant primary sporocyst development has been attained for several other digeneans including S. japonicum and Fascioloides magna. Here we review recent advances in the cultivation of several larval trematode species and discuss the potential use of this culture system for addressing fundamental questions of host-parasite compatibility.