Definition of Schistosomiasis:

Schistosomiasis is infection with a type of Schistosoma parasite.

Causes, incidence, and risk factors:

You get a schistosoma infection through contact with contaminated water. The parasite in its infective stages is called a cercaria. It swims freely in open bodies of water.

On contact with humans, the parasite burrows into the skin, matures into another larval stage (schistosomula), then migrates to the lungs and liver, where it matures into the adult form.

The adult worm then migrates to its preferred body part, depending on its species. These areas include the bladder, rectum, intestines, liver, portal venous system (the veins that carry blood from the intestines to liver), spleen, and lungs.

Schistosomiasis is not usually seen in the United States. It is common in many tropical and subtropical areas worldwide, where it affects more than 200 million people.

Symptoms:

Symptoms vary with the species of worm and the phase of infection.

• Heavy infestation (many parasites) may cause fever, chills, lymph node enlargement, and liver and spleen enlargement.
• Initial invasion of the skin may cause itching and a rash (swimmer's itch). In this condition, the schistosome is destroyed within the skin.
• Intestinal symptoms include abdominal pain and diarrhea (which may be bloody).
• Urinary symptoms may include frequent urination, painful urination (dysuria), and blood in the urine (hematuria).

Signs and tests:

• Anemia (low number of red blood cells)
• Antibody test (checks for schistosome antigens)
• Biopsy of tissue suspected of being infected
• High eosinophil (a type of white blood cell) count in blood
• Low platelets
• Test for schistosome eggs in stool
• Test for schistosome eggs in urine
• Urinalysis

Treatment:

This infection is usually treated with the drug Praziquantel. If the infection is severe or involves the brain, corticosteroids may be given.

Expectations (prognosis):

Treatment before significant damage or severe complications occur usually produces good results.

Complications:

• Bladder cancer
• Chronic kidney failure
• Chronic liver damage and an enlarged spleen
• Colon (large intestine) inflammation with bloody diarrhea
• Kidney and bladder obstruction
• Pulmonary hypertension
• Repeated blood infections can occur, because bacteria can enter the bloodstream through an irritated colon
• Right-sided heart failure
• Seizures

Calling your health care provider:

Call your health care provider if you develop symptoms of schistosomiasis, especially if you have traveled to a tropical or sub-tropical area where the disease is known to exist or if you have been exposed to contaminated or suspect bodies of water.

Prevention:

• Avoid swimming or bathing in contaminated or potentially contaminated water
• Avoid bodies of water of unknown safety

Snails are an intermediate host for the parasite. Getting rid of snails in bodies of water used by humans would help prevent infection.