S. mansoni is transmitted by snail species of the genus Biomphalaria (Figure 52.9), which is widely distributed throughout Africa, the Nile valley and the Arabian Peninsula, but not in Iraq or Iran. In the Americas, the genus is found in the southern USA, several Caribbean islands (notably Puerto Rico, St Lucia, Guadeloupe and the Dominican Republic) and on the South American continent in Brazil, Surinam and Venezuela.
In Africa, the only species of schistosome are S. intercalatum, S. mansoni, and S. haematobium. S. haematobium causes urinary schistosomiasis, so eggs will be shed in the urine; S. mansoni and S. intercalatum reside in the mesenteric venous plexus, so eggs will be shed in the feces.
Schistosomiasis is an infection caused mainly by three schistosome species; Schistosoma mansoni, Schistosoma japonicum and Schistosoma haematobium. S. japonicum being the most infectious of the three species. Infection by schistosomes is followed by an acute Katayama fever.