Definition of Schistosomiasis:

Schistosomiasis is infection with a type of Schistosoma parasite.

Causes, incidence, and risk factors:

You get a schistosoma infection through contact with contaminated water. The parasite in its infective stages is called a cercaria. It swims freely in open bodies of water.

On contact with humans, the parasite burrows into the skin, matures into another larval stage (schistosomula), then migrates to the lungs and liver, where it matures into the adult form.

The adult worm then migrates to its preferred body part, depending on its species. These areas include the bladder, rectum, intestines, liver, portal venous system (the veins that carry blood from the intestines to liver), spleen, and lungs.

Schistosomiasis is not usually seen in the United States. It is common in many tropical and subtropical areas worldwide, where it affects more than 200 million people.