Health Encyclopedia

Schistosomiasis

Definition

Schistosomiasis is an infection caused by one of the five species of the parasite Schistosoma.

Alternative Names

Bilharzia; Katayama fever; Swimmer's itch; Blood fluke

Causes, incidence, and risk factors

Schistosoma infections are contracted 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 the anatomic area of its preference, depending on which species is involved. Likely areas include the bladder, rectum, intestines, liver, portal venous system (the veins that serve the liver), spleen, and lungs.

Schistosomiasis is not usually found in the United States. However, it is common in many tropical or subtropical areas, and it is a common illness thought to affect more than 200 million people.

Symptoms

Symptoms vary with the species of worm and the phase of infection.
Initial invasion of the skin may cause itching and a rash (swimmer's itch).
Heavy infestation (a large number of parasites) may cause fever, chills, lymph node enlargement, and liver and spleen enlargement.
Urinary symptoms may include frequent urination, painful urination (dysuria), and blood in the urine (hematuria).
Intestinal symptoms include abdominal pain and diarrhea (which may be bloody).

Signs and tests

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

Treatment

Praziquantel
With acute infection, corticosteroids may be given

Expectations (prognosis)

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

Complications

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

Calling your health care provider

Call your health care provider if you have traveled to an area where the disease is known to exist, have had exposure to contaminated or suspect bodies of water, or have developed symptoms suggestive of schistosomiasis.

Prevention

Avoid swimming or bathing in water known to be contaminated or potentially contaminated
Avoid bodies of water of unknown safety

Eradication of snails (an intermediate host for the parasite) in bodies of water used by humans would help prevention efforts.

Review Date:9/5/2006
Reviewed By:D. Scott Smith, M.D., MSc, DTM&H, Chief of Infectious Disease & Geographic Medicine, Kaiser Redwood City, CA & Adjunct Assistant Professor, Stanford University. Review provided by VeriMed Healthcare Network.

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