Human blood fluke disease, also called schistosomiasis or bilharziasis, is a major parasitic disease affecting over 200 million people worldwide, mostly those in the tropics. Although sometimes fatal, schistosomiasis more commonly results in chronic ill-health and low energy levels. The disease is caused by small parasitic flatworms of the genus Schistosoma. Of the three species, two (S. haematobium and S. mansoni) are found in Africa and the Middle East, the third (S. japonicum) in the Orient. Schistosoma haematobium lives in the blood vessels of the urinary bladder and is responsible for over 100 million human cases of the disease a year. Schistosoma mansoni and Schistosoma japonicum reside in the intestine; the former species infect 75 million people a year and the latter 25 million.

Schistosomiasis is spread when infected people urinate or defecate into open waterways and introduce parasite eggs that hatch in the water. Each egg liberates a microscopic free-living larva...