The Pathogen These species differ biologically from one another and in their geographic distribution and the type of disease that they produce The schistosomes are digenetic parasitic trematodes. Although they are morphologically distinct, the species of Schistosoma that infect humans share some common factors7 The Pathogen  These species differ biologically from one another and in their geographic distribution and the type of disease that they produce.  The schistosomes are digenetic parasitic trematodes.Although they are morphologically distinct, the species of Schistosoma that infect humans share some common factors