Schistosomiasis

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Schistosomiasis is infection caused by certain flatworms (flukes), called schistosomes.

People acquire schistosomiasis by swimming or bathing in fresh water that is contaminated with the flukes.
The infection may cause an itchy rash, then after several weeks, fever, chills, muscle aches, fatigue, nausea, abdominal pain, and, later, other symptoms depending on which organ is affected.
Doctors confirm the diagnosis of schistosomiasis by identifying eggs in a sample of stool or urine.
The infection is treated with praziquantel .

Flukes are parasitic flatworms. There are many species of flukes. Different species tend to infect different parts of the body. Schistosomiasis is the most common type of fluke infection. It affects over 221 million people in tropical and subtropical regions of South America, Africa, and Asia. (See also Overview of Parasitic Infections.)
Five Schistosoma species develop into adult flukes in people and account for most of the cases of schistosomiasis:

Schistosoma hematobium infects the urinary tract (including the bladder). This species is widely distributed over the African continent and occurs in some parts of the Middle East, Turkey, and India.
Schistosoma mansoni, Schistosoma japonicum, Schistosoma mekongi, and Schistosoma intercalatum infect the intestine and liver. Schistosoma mansoni is widespread in Africa and is the only schistosome in the Western Hemisphere (in parts of South America and the Caribbean). Schistosoma japonicum and Schistosoma mekongi occur in Asia and Southeast Asia. Schistosoma intercalatum occurs in Central and West Africa.

None of these five Schistosoma species cause schistosomiasis in people who live in Canada or the United States, including Puerto Rico, where schistosomiasis used to be endemic.
Schistosomiasis is acquired by swimming, wading, or bathing in fresh water that is contaminated with the free-swimming stage of the parasite.
An infected person passes schistosome eggs in stool or urine. In water, the eggs release immature larvae (called miracidia), which enter specific types of water-dwelling snails, multiply, and mature into a form called cercariae, which can swim. The cercariae are released to swim free in the water. If they encounter a person’s skin, they burrow in and move through the bloodstream to the liver, where they mature into adult flukes. The adults travel to their final home in small veins in the bladder or intestine (depending on the species), where they live an of average 3 to 10 years. The adult flukes lay large numbers of eggs in the walls of the intestine or bladder. The eggs cause local tissue damage and inflammation, which may result in ulcers, bleeding, and scar tissue formation. Some eggs pass into the stool (feces) or urine. If urine or stool of infected people enters fresh water, the eggs hatch, releasing immature larvae, which enter snails to begin the cycle again.
Schistosoma mansoni and Schistosoma japonicum typically lodge in small veins of the intestine. Some eggs flow from there through the bloodstream to the liver. The resulting liver inflammation can lead to scarring and increased pressure in the vein that carries blood between the intestinal tract and the liver (the portal vein). High blood pressure in the portal vein (portal hypertension) can cause enlargement of the spleen and bleeding from veins in the esophagus.
The eggs of Schistosoma hematobium typically lodge in the bladder, sometimes causing ulcers, bleeding into the urine, and scarring. Schistosoma hematobium infection increases the risk of bladder cancer.
All types of schistosomiasis can affect other organs (such as the lungs, spinal cord, and brain). Eggs that reach the lungs can result in inflammation and increased blood pressure in the arteries of the lungs (pulmonary hypertension), which can result in a type of heart failure called cor pulmonale.
Adult schistosomes live on average 3 to 10 years, but sometimes longer. Females are about 1/4 to 3/4 inch long. Males are slightly smaller.