Schistosomiasis

Schistosomiasis, also known as bilharzia, bilharziosis or snail fever, currently infects 200 million people in 74 endemic countries, primarily women and school-aged children. It is also considered a Neglected Tropical Disease (NTD). For more information about NTDs, click here. Estimates indicate that more than 200,000 deaths result from schistosomiasis each year.

Infections occur when a person comes in contact with fresh water that is infested with contaminated snails. Thousands of parasites, known as cercariae, emerge daily from the snail host into fresh water.  They penetrate human skin by secreting enzymes that break down the skin's protein, which allows the cercarial head to enter through the skin.  From there the parasite travels to the lungs where it undergoes developmental changes so it can migrate to the liver. The parasite usually reaches the liver, where it feeds on red blood cells, within 8 days of penetration. Parasites reach maturity in six to eight weeks, at which time they begin to pair up and produce eggs. Many of the eggs pass through the walls of the blood vessels, and through the intestinal wall to be passed out of the body in feces. Some eggs pass through the ureteral or bladder wall and into urine. Up to half the eggs released by the worm pairs are washed back into the liver, where they become lodged. Worm pairs can live in the body for an average of four and a half years, but may persist up to 20.

The infection can lead to stunted growth and development and in severe cases, to bladder cancer and kidney, liver, and spleen malfunction. Schistosomiasis, along with hookworm, is particularly dangerous during pregnancy because it can cause neonatal prematurity, reduced neonatal birth weight, and increased maternal morbidity and mortality. For more information about hookworm, click here.

In those areas where the infection is endemic, schistosomiasis can be treated with a single dose of praziquantel, a highly effective oral medication with a long shelf-life that can be administered safely after minimal training.  The medication cures the current infection but does not prevent re-infection which is accomplished through behavior change, including appropriate sanitation and hygiene and education. HKI currently has programs to combat schistosomiasis in Mali and Sierra Leone.