What is schistosomiasis?

According to the World Health Organization, 240,000 people are infected by schistosomiasis each year, with an additional 790 million people at risk in 74 endemic countries. Schistosomiasis is a parasite spread through  freshwater snails who act as the intermediate host.  Humans put themselves at risk if they spend time in rivers, streams, lakes and canals with the nearly invisible infected snails, who release the larval form of the parasite (cercariae) that penetratse human skin. Chronic schistosomiasis causes infections in the intestines, liver, bladder, and spleen, liver, kidney and bladder fibroses that lead to organ failure.

Children with enlarged livers and spleens from schistosomiasis

The larval forms of the parasite, released by the snail, burrow into the human skin and reproduce inside of the human body.  The females release 400-1,000 eggs per day, some of which remain in the body, triggering an immune response that eventually causes granulomas and severe organ damage, and some of which exit the body through the urine or feces.  Because human waste often ends up in the local water, the eggs released in the urine and feces are re-introduced into the water, infecting snails, and allowing for a vicious cycle of infection and re-infection.

 

 

 

 

 

*Taken from The Merck Manual.  Merck is the manufacturer of the only treatment, a drug called praziquantal.

Depending on the stage of the disease, symptoms can vary.  Usually, intestinal schistosomaisis is identified by diarrhea, blood in the stool, and abdominal pain.  Urinary schistosomiasis can be recognized by blood in the urine (haematuria).  A diagnosis is concluded when parasite eggs are found in stool or urine, for intestinal and urinary schistosomaisis, respectively.