Schistosomiasis



Schistosomiasis (shis-to-so-MY-a-sis), also known as bilharzia (bil-HAR-zee-a), is a disease caused by parasitic worms that affects more than 200 million people worldwide.

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Parasites

Schistosomiasis is caused by parasitic * worms called blood flukes of the genus Schistosoma. Three species within the genus (Schistosoma mansoni, S. japonicum, and S. haematobium) are responsible for most infections. Blood flukes live in water in tropical areas of the world and are common in Africa, South America (Brazil, Venezuela, and Surinam), parts of the Caribbean (Saint Lucia, Antigua, Montserrat, Martinique, Guadeloupe, the Dominican Republic, and Puerto Rico), some Middle Eastern countries, parts of China, the Philippines, and Southeast Asia. Contact with contaminated water through bathing, swimming, or wading is the most common method of infection.

* parasitic means caused by creatures that live in and feed on the bodies of other organisms. The animal or plant carrying the parasite is called its host.

What Is the Life Cycle of Schistosoma?

Freshwater rivers, lakes, and streams become contaminated when people who have schistosomiasis urinate or defecate in the water, leaving behind

A woman and children wash clothes in a pond that contains snails carrying fluke worms in Morogoro, Tanzania. The snails release infective larvae into fresh water. Andy Crump, TDR, WHO/Science Photo Library/Custom Medical Stock Photo.
A woman and children wash clothes in a pond that contains snails carrying fluke worms in Morogoro, Tanzania. The snails release infective larvae into fresh water.
Andy Crump, TDR, WHO/Science Photo Library/Custom Medical Stock Photo.
blood fluke eggs. After the eggs hatch, the Schistosoma larvae * attack a certain species of snail (if the snail is not present, the larvae will die). After the snail is infected, the larvae grow and develop in the snail. When the larvae leave the snail, if they come in contact with a human within 48 hours they burrow into the skin and enter blood vessels. The parasites then grow in the bloodstream, where they produce eggs. Some of the eggs travel to the liver. Others enter the intestine or the urinary bladder, where they pass out of the body through urine or stool. If the eggs reach a freshwater supply, the cycle begins again.

What Are the Signs and Symptoms of Schistosomiasis?

Initially, skin may be itchy and a rash may appear where the Schistosoma burrow into the skin. As the worms develop in the liver, fever, chills, cough, and muscle aches may develop. There may be liver enlargement or malfunction, diarrhea, abdominal pain, and vomiting. The kidneys may be also affected. In rare cases, eggs can reach the brain or spinal cord and cause seizures. Even without treatment, most cases do not result in permanent damage to organs, though there may be significant long-term health effects.

Sometimes, however, the infection scars the liver so much that blood flow through the liver is partially blocked. This causes a condition called portal hypertension (POR-tal HY-per-ten-shun), which may cause sometimes fatal bleeding from swollen veins in the stomach and esophagus * .

How Is Schistosomiasis Diagnosed and Treated?

Schistosomiasis is diagnosed by identifying eggs in stool or urine samples. Repeated samples may be required to identify the parasite. Blood tests may be used to identify the need to search for eggs but are not usually enough to make decisions about treatment. Treatment depends on the severity of the infection. A drug called praziquantel (pra-zi-KWAN-tel) is used to treat the infection.

How Is Schistosomiasis Prevented?

In many parts of the world, there is no way of knowing whether water is contaminated with blood fluke larvae. It is best to avoid any contact with fresh water in areas where Schistosoma are known to occur. Swimming in ocean water and chlorinated pools is generally considered safe.

* larvae are worms at an intermediate stage of the life cycle between eggs and adulthood.

* esophagus (e-SOF-a-gus) is the tube connecting the stomach and the throat.

The U.S. and the World

Schistosomiasis is a leading cause of illness in tropical areas of the world. According to the World Health Organization (WHO), only malaria is considered more widespread among tropical ill-nesses. More than 20 million people worldwide suffer severe consequences of schistosomiasis, and about 120 million show symptoms. Overall, about 200 million people are infected and 600 million are at risk. WHO estimates that more than 80 percent of all the people infected with schistosomiasis live in sub-Saharan Africa. The infection leads to an estimated 20,000 deaths each year. United States residents can get schistosomiasis when traveling to other parts of the world where the disease occurs; schistosomiasis has even struck some Americans who were on African river-rafting trips.

Resources

Organizations

Centers for Disease Control and Prevention, 100 Clifton Road N.E., Bldg. 1, SSB249, MS A34, Atlanta, GA 30333. This U.S. agency helps control communicable, carrier-borne, and occupational diseases and prevent disease, injury, and disability. A fact sheet on schistosomiasis is available on its website.
Telephone 404-639-3534
http://www.cdc.gov/ncidod/dpd/schisto.htm

World Health Organization, 2 United Nations Plaza, 2 Building, Rooms 0956-0976, New York, NY 10017. A United Nations agency dedicated to achieving the best health possible for people worldwide. Public health information is available on its website.
Telephone 212-963-4388
http://www.who.int/

See also
Parasitic Diseases

Also read article about Schistosomiasis from Wikipedia

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