infection with flukes (trematodes) of the genus SCHISTOSOMA. Three species produce the most frequent clinical diseases: schistosoma haematobium (endemic in africa and the middle east), schistosoma mansoni (in egypt, northern and southern africa, some west indies islands, northern 2/3 of south america), and schistosoma japonicum (in japan, china, the philippines, Celebes, thailand, laos). S. mansoni is often seen in Puerto Ricans living in the united states.