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Schistosomiasis

Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans. Although schistosomiasis is not found in the United States, more than 200 million people are infected worldwide.

What is schistosomiasis?

Schistosomiasis, also known as bilharzia (bill-HAR-zi-a), is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans. Although schistosomiasis is not found in the United States, more than 200 million people are infected worldwide.​

How can I get schistosomiasis?

Infection occurs when your skin comes in contact with contaminated freshwater in which certain types of snails that carry schistosomes are living. Freshwater becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and if certain types of snails are present in the water, the parasites grow and develop inside the snails. The parasite leaves the snail and enters the water where it can survive for about 48 hours. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing, or washing in contaminated water. 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.

What are the symptoms of schistosomiasis?

Within days after becoming infected, you may develop 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. Eggs travel to the liver or pass into the intestine or bladder, causing inflammation or scarring. Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of infection, the parasite can also damage the liver, intestines, lungs, and bladder. Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, or spinal cord inflammation. Symptoms of schistosomiasis are caused by the body's reaction to the eggs produced by worms, not by the worms themselves.

What should I do if I think I have schistosomiasis?

See your health care provider. If you have traveled to countries where schistosomiasis is found and had contact with freshwater, describe in detail where and for how long you traveled. Explain that you may have been exposed to contaminated water.

How is schistosomiasis diagnosed?

Your health care provider may ask you to provide stool or urine samples to see if you have the parasite. A blood test has been developed and is available at CDC. For accurate results, you must wait six to eight weeks after your last exposure to contaminated water before the blood sample is taken.

What is the treatment for schistosomiasis?

Safe and effective drugs are available for the treatment of schistosomiasis. You will be given pills to take for 1-2 days.

Am I at risk?

If you live in or travel to areas where schistosomiasis occurs and your skin comes in contact with freshwater from canals, rivers, streams, or lakes, you are at risk of getting schistosomiasis.

In what areas of the world does schistosomiasis occur?

  • Africa: all freshwater in southern and sub-Saharan Africa–including the great lakes and rivers as well as smaller bodies of water–is considered to be at risk for schistosomiasis transmission. Transmission also occurs in the Nile River valley in Egypt.
  • South America: including Brazil, Suriname, Venezuela
  • Caribbean: Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (risk is low)
  • The Middle East: Iran, Iraq, Saudi Arabia, Yemen
  • Southern China
  • Southeast Asia: Philippines, Laos, Cambodia, central Indonesia, Mekong delta

How can I prevent schistosomiasis?

  • Avoid swimming or wading in freshwater when you are in countries in which schistosomiasis occurs. 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, you should either boil water for 1 minute or filter water before drinking it. Boiling water for at least 1 minute will kill any harmful parasites, bacteria, or viruses present. Iodine treatment alone will not guarantee that water is safe and free of all parasites.
  • Bath water should be heated for 5 minutes at 150°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 may help to prevent the Schistosoma parasite from penetrating the skin. You should not rely on vigorous towel drying to prevent schistosomiasis.

Content courtesy of the Centers for Disease Control and Prevention: Schistosomiasis Fact Sheet.

Research

NIAID-supported researchers are studying many diverse aspects of schistosomiasis to find new ways to prevent and treat the disease. Due to the unique lifecycle of the schistosome, the parasitic worm that causes schistosomiasis, researchers can study the disease and its debilitating effects during various stages: the waterborne egg stage, the intermediate snail host, or the parasite’s adult phase which takes place in humans. With the recently sequenced genomes of multiple species of schistosome parasites, researchers can move forward in developing valuable vaccines and therapeutics for schistosomiasis.

Treatment

Public health experts are concerned about schistosomes becoming resistant to the currently used drug, praziquantel. If this were to occur, an alternative drug would be needed as a substitute. To fulfill this need, NIAID-supported researchers are conducting basic research to learn more about certain biochemical pathways that the schistosome worm requires for survival. If a drug could target these pathways and inhibit them, this would be a new and effective way to eliminate the parasite.

Vaccine

A safe and effective vaccine is an important part of controlling the transmission of schistosomiasis. Researchers are currently working on improving the efficacy of identified vaccine candidates and are also conducting studies to better understand the mechanisms by which those vaccines elicit an immune response in animal models.

Genomics

Recently, the genomes of two schistosomiasis-causing parasites were sequenced: Schistosoma mansoni and Schistosoma japonicum. The information from the analysis of these genomes may help researchers find new ways to treat the disease. For example, investigators have begun to uncover the metabolic reactions that are encoded in the worm’s genetic sequences. As a next step, it may be possible to design a drug that disables the identified metabolic processes, thereby inhibiting the schistosome’s development.

NIAID Schistosomiasis Resource Center

Much of the schistosomiasis research in the United States is made possible by the NIAID Schistosomiasis Resource Center. For more information on this unique repository, please read Unique NIAID Resource Helps Researchers Combat Parasitic Worm Disease.

Tropical Medicine Research Centers

In 2012, NIAID funded eight Tropical Research Medicine Centers (TMRCs) to support research on neglected tropical diseases (NTDs), including schistosomiasis, in endemic areas. The Centers are designed to facilitate research on the cause, diagnosis, prevention and treatment of NTDs, and to create and sustain in-country research capacity. The TMRC program also supports clinical and field site development. A major outcome of this research program is to build capacity to enable TMRCs to conduct future clinical trials and implement new treatment, control and prevention strategies.

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Last Updated August 08, 2012