Schistosomiasis

Schistosomiasis, also called bilharzia, is a long-lasting infection with parasitic flatworms of the genus Schistosoma, the blood flukes. Counted among the neglected tropical diseases, it is most common in Africa but also occurs in parts of the Middle East, South America and Asia. Infection happens when people wade, bathe, fish or wash in fresh water holding cercariae, free-swimming larvae released by certain snails. The cercariae bore through the skin, enter the blood and mature in the veins, where male and female worms pair up and can live for years.

The adult worms do little harm themselves; the damage comes from their eggs. Some eggs leave in feces or urine and, on reaching fresh water, hatch and infect snails, but many get trapped in tissues and provoke inflammation and scarring. In intestinal schistosomiasis, caused mainly by S. mansoni and S. japonicum, this brings abdominal pain, bloody diarrhea and an enlarged liver and spleen. In urogenital schistosomiasis, caused by S. haematobium, blood in the urine is the classic sign, and long infection can scar the bladder and raise the risk of bladder cancer. Infected children may develop anemia and fall behind in growth and learning.

Diagnosis is by finding eggs in stool or urine or by antigen tests, and the drug praziquantel treats all species.