Schistosoma mansoni: suramin and trypan blue in vitro and the ultrastructure of feeding schistosomules.

The in vitro effects of suramin and trypan blue on schistosomules of Schistosoma mansoni were examined by light and electron microscopy. The drugs were administered to 12-day cultures of schistosomules produced by the penetration method. The larvae were maintained on mouse red blood cells for 5 days prior to addition of the drugs. At the concentrations used, the morphological changes attributable to the drugs were identical for the two drugs. The first signs of anomaly were observable at 8 hr after exposure. At this time, the digestive system showed signs reminiscent of early starvation effects such as alterations of the Golgi and an increase of autophagy. After 36 hr, a rapid disintegration of the gastrodermis became evident. It was hypothesized that the drugs initially inhibit the digestive enzymes and, subsequently, labilize the luminal plasma membrane of the gastrodermis. By 48 hr after exposure, the larvae were dead.