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Schistosomiasis

• Schistosomiasis [shis-to-so-MY-uh-sis] is a disease of the tropics that can lead to serious, long-term illness.
• Schistosomiasis is caused by parasitic flatworms.
• People get schistosomiasis by contact with fresh water containing flatworm eggs.
• Schistosomiasis is treatable.
• To prevent schistosomiasis, avoid swimming or wading in fresh water when visiting areas where the disease is known to occur.

What is schistosomiasis?

Schistosomiasis is a tropical disease that can cause serious, long-term illness. Schistosomiasis is also called bilharzia [bill-HAR-zi-a].

What is the infectious agent that causes schistosomiasis?

Schistosomiasis is caused by parasitic flatworms, called schistosomes. Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium cause illness in humans. The worms live in fresh water in the tropics. To infect humans, the worms must first infect and mature in freshwater snails, which are their "intermediate hosts."

Where is schistosomiasis found?

Schistosomiasis is found in these parts of the world:

• Africa: Southern Africa, sub-Saharan Africa, Lake Malawi, Nile River valley in Egypt
• Latin America: Brazil, Suriname, Venezuela, Antigua, Dominican Republic, Guadeloupe
• Caribbean: Martinique, Montserrat, Puerto Rico, St. Lucia (low risk)
• Middle East: Iran, Iraq, Saudi Arabia, Syrian Arab Republic, Yemen
• Southern China
• Southeast Asia: Philippines, Laos, Cambodia, Japan, central Indonesia, Mekong delta

How do people get schistosomiasis?

People get schistosomiasis by skin contact with contaminated fresh water in which certain types of snails that carry schistosomes are living.

Infected people pass Schistosoma eggs in their urine and stool. The eggs get into fresh water sources when infected people urinate or defecate in the water. The eggs hatch in the water and seek out the snails they need to survive. Once in the snails, the parasites grow, reproduce, and are released into the water, where they can live for about 48 hours.

The parasites can penetrate the skin of persons who are using the water for washing or bathing, swimming, or work activities such as fishing, rice cultivation, or irrigation. Within several weeks, worms grow inside the blood vessels of the body and produce eggs. Some of these eggs travel to the bladder or intestines and are passed into the urine or stool.

Only about half of the eggs are passed in the urine or stool. The rest stay in the body where they can scar and damage vital organs. The symptoms of the disease are caused by the body's reaction to the worms' eggs, not by the worms themselves.

What are the signs and symptoms of schistosomiasis?

Within days after becoming infected, some people have a rash or itchy skin. Fever, chills, cough, and muscle aches can begin within 1-2 months of infection. Most people have no symptoms at this early phase of infection.

Later symptoms are related to the number and location of parasite eggs in the body. Eggs travel to the liver or pass into the intestine or bladder, causing symptoms related to these organs. In rare cases, eggs can travel to the brain or spinal cord and cause seizures, paralysis, or spinal cord inflammation.

How is schistosomiasis diagnosed?

Schistosomiasis is diagnosed by testing the urine or stool for parasites. A blood test has been developed and is available at CDC. For accurate results, a blood sample should be taken 6-8 weeks after the last exposure to contaminated water.

Who is at risk for schistosomiasis?

Persons who live in or travel to areas where schistosomiasis occurs and who have skin contact with fresh water (river, streams, lakes, canals) are at risk of getting schistosomiasis. Schistosomiasis has been reported in U.S. river rafters in Africa, tourists who swam in contaminated waters, and Peace Corps volunteers and others who had contact with fresh water in areas where schistosomiasis occurs.

What is the treatment for schistosomiasis?

The disease is treatable, usually with the drug praziquantel taken for 1-2 days.

What complications can result from schistosomiasis?

For those who go without treatment for a long time, schistosomiasis can be hard to cure. There can be lifelong damage to the liver, lungs, intestines, or bladder. For those who are exposed only briefly, such as during travel, and who are not reinfected, complications are rare even without treatment.

How common is schistosomiasis?

Schistosomiasis is not found in the United States, but an estimated 200 million people are infected worldwide. The presence of widespread schistosomiasis in a country is usually a sign of problems in sanitary waste disposal and treatment. The long-term illnesses that result from the infection can have serious consequences for a country's socioeconomic development.

Is schistosomiasis an emerging infectious disease?

Yes. Schistosomiasis is an increasing problem around the world as countries build and develop new agricultural and water resources and as more people are exposed to infection. Refugee movement in Africa, the Eastern Mediterranean, and Asia, and construction of dams, reservoirs, and irrigation systems are introducing schistosomiasis to new areas and increasing the spread of infection. The growing popularity of wilderness tourism is exposing more travelers.

How can schistosomiasis be prevented?

Follow these precautions when in countries where schistosomiasis occurs:

• Avoid swimming or wading in fresh water. Swimming in the ocean and in chlorinated swimming pools is generally thought to be safe.
• Drink safe water. Because there is no way to make sure that water coming directly from canals, lakes, rivers, streams, or springs is safe, either boil water for 1 minute or filter water before drinking it. Boiling water for at least 1 minute will kill any parasites, bacteria, or viruses present. Iodine treatment alone will not guarantee that water is safe and free of all parasites.
• Heat bath water for 5 minutes at 150^o F. Water held in a storage tank for at least 48 hours should be safe for showering.
• Vigorous towel drying after an accidental, very brief water exposure might help to prevent the Schistosoma parasite from penetrating the skin. However, do not rely on vigorous towel drying to prevent schistosomiasis.

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have questions about the disease described above, consult a health-care provider.

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