Schistosoma

A genus of trematodes, Schistosoma, commonly known as blood-flukes and bilharzia, includes flatworms which are responsible for a highly significant parasitic infection of humans by causing the disease schistosomiasis, and is considered by the World Health Organization as the second most socioeconomically devastating parasitic disease, next only to malaria, with hundreds of millions infected worldwide.

Adult worms parasitize mesenteric blood vessels. They are unique among trematodes or any other flatworms in that they are dioecious with distinct sexual dimorphism between male and female. Eggs are passed through urine or feces to fresh water, where larva must pass through an intermediate snail host, before a different larval stage of the parasite emerges that can infect a new mammalian host by directly penetrating the skin.