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Schistosoma/Schisotsomiasis

Roundworm—Schistosoma causes Schistosomiais (Swimmer’s itch) or Bilharziasis

Schistosomiasis, also known as bilharziasis, swimmer’s itch or snail fever, is a primarily tropical parasitic disease caused by the larvae of one or more of five types of flatworms or blood flukes known as schistosomes. All five species are contracted in the same way, through direct contact with fresh water infested with the free-living form of the parasite known as cercariae. The building of dams, irrigation systems, and reservoirs, and the movements of refugee groups introduce and spread schistosomiasis. Eggs are excreted in human urine and feces and, in areas with poor sanitation, contaminate freshwater sources.

The eggs break open to release a form of the parasite called miracidium.

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Schistosomas miracidium

Freshwater snails become infested with the miracidium, which multiply inside the snail and mature into multiple cercariae that the snail ejects into the water.

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Schistosoma cercaria

The cercariae, which survive outside a host for 48 hours, quickly penetrate unbroken skin, the lining of the mouth, or the gastrointestinal tract. Once inside the human body, the worms penetrate the wall of the nearest vein and travel to the liver where they grow and sexually mature. Mature male and female worms pair and migrate either to the intestines or the bladder where egg production occurs.

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Schistosomiasis japonicum egg

One female worm may lay an average of 200 to 2,000 eggs per day for up to twenty years. Most eggs leave the blood stream and body through the intestines. Some of the eggs are not excreted, however, and can lodge in the tissues. It is the presence of these eggs, rather than the worms themselves that causes the disease.

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Schistosoma mansoni egg

Symptoms of Schistosomiasis infection: Many individuals do not experience symptoms. The first symptom of the disease may be a general ill feeling. Within twelve hours of infection, an individual may complain of a tingling sensation or light rash, commonly referred to as “swimmer’s itch,” due to irritation at the point of entrance. Other symptoms can occur two to ten weeks later and can include fever, aching, cough, diarrhea, or gland enlargement.

With intestinal Schistosomiasis obstruction of the colon and blood loss can occur. Potbelly look, high blood pressure, enlarged spleen, ascites (build up of fluid in the abdomen), swollen areas in the esophagus and sometimes nervous system can be affected.  

With urinary tract Schistosomiasis there is blood in the urine with associated iron deficiency anemia, pain upon urinating, increased frequency of urination, blocked urinary tracts and sometimes bladder cancer.

Diagnosis of Schistosomiasis: Malaria, typhoid and scabies all have to be ruled out as they look very similar to Schistosomiasis. Has the patient traveled to third-world countries? Is the eosinophil white blood count elevated? Are there eggs evident in the urine or feces? Blood in the urine? Don’t hesitate to repeat fecal tests several times as the eggs may not show up for several months. There is an antigen test for the Schistosoma parasite although it may not be readily available in the United States. Ultrasound, CAT scan and MRI may be indicated to detect damage to the blood vessels, liver and to detect polyps and ulcers caused by the parasite.

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"Swimmers itch" Cercaria dermatitis

Treatment of Schistosomiasis: Praziquantel (Biltricide), oxamniquine (intestinal signs), metrifonate (for urinary forms)  

Prevention of Schistosomiasis: Water systems must be treated to kill the worms and control snail populations, and sanitation must be improved to prevent the spread of the disease.

Prevention Tips for Schistosomaisis in Endemic Areas:

  • Contact the Center for Disease Control for current health information on travel destinations.
  • Upon arrival, ask an informed local authority about the infestation of Schistosomaisis before being exposed to freshwater in countries that are likely to have the disease.
  • Do not swim, stand, wade, or take baths in untreated water.
  • Treat all water used for drinking or bathing. Water can be treated by letting it stand for three days, heating it for five minutes to around 122°F (around 50°C), or filtering or treating water chemically, with chlorine or iodine, as with drinking water.
  • Should accidental exposure occur, infection can be prevented by hastily drying off or applying rubbing alcohol to the exposed area.

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