Alternative names
Bilharzia; Katayama fever; Swimmer’s itch; Blood fluke

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

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, spleen, and lungs.

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


  • 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 may cause fever, chills, lymph node enlargement, and liver and spleen enlargement.  
  • Urinary symptoms may include frequency, painful urination (dysuria), and blood in 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 having infection  
    • Anemia  
    • High eosinophil 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 usually produces good results.


      • Kidney and bladder obstruction  
      • Chronic renal failure  
      • Bladder cancer  
      • Chronic liver damage with an enlarged spleen  
      • Colon inflammation with bloody diarrhea  
      • Pulmonary hypertension  
      • Right-sided heart failure  
      • Seizures  
      • Recurrent 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.


      • 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 areas used by humans


      Johns Hopkins patient information

      Last revised: December 3, 2012
      by Martin A. Harms, M.D.

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