Flow diagram demonstrating how schistosome transmission may persist despite the use of adequate sanitation. Schistosome eggs hatch upon entry into freshwater, and release miracida. These miracidia cannot survive for long without infecting an intermediate host, so miracidia in adequate sanitation systems are unlikely to contribute to transmission (point 1). However, it is possible that some eggs may enter freshwater as a result of washing off the bodies or soiled clothing of those infected (point 2). Reservoir hosts provide another potential source of miracidia (point 3).