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Schistosomiasis (Snail Fever)

Schistosomiasis is a parasitic infection caused by 5 distinct species of Schistoma: S. Mansoni, S. Japonicum, S. Mekong, S. Hematobium and S. Intevcalatum. The infection is spread by snails that release larvae (miracidia) into fresh water which gain entry into humans by penetrating their skin as they walk in water.

The infection can have an acute phase producing an itchy rash (swimmer itch), a subacute phase of fever and a chronic phase due to obstruction of organs with heavy worms load.

Where does it occur?

S. Mansoni: Africa, South America, Carribean, and the Arabian Peninsula

S. Japonicum: Japan, China, and Philippines S. Mekong: Southeast Asia

S. Hematobium: Africa and Middle East

 S. Intevcalatum: Central and West Africa

How is it transmitted?

Infection is acquired by humans after the larvae penetrate through intact skin as they are working, wading, swimming or bathing in freshwater barefoot.

Is it contagious from person to person?


What is the risk for travelers?

There is a moderate risk to travelers. Outbreaks have occurred on rafting trips in high risk countries. Long term visitors like volunteers, researchers and aid workers are also at risk.

How soon after exposure will one develop symptoms?

Acute symptoms of red rash can be seen within 24 hours of exposure, sub-acute symptoms of fever can be seen in 4-6 weeks. Effects of chronic infection take months to years.

What are the signs and symptoms?

Rarely a rash can be seen as the initially manifestation but it usually does not occur on the 1st exposure. Within 24 hours of the 2nd or 3rd exposure, one can sometimes see a red itchy rash that resolves.

Approximately 4-8 weeks after exposure one can see a cluster of symptoms called “Katayama” fever including fever, chills headache, sweating, cough abdominal pain and diarrhea. These symptoms resolve in a few weeks.

Manifestations of chronic infection depend on the organ system involved. With S. mansoni, S. japonicum and S. intercalatum infections, eggs lodge in the liver and intestine causing enlargement of the liver, spleen and bleeding from the esophagus or intestines. As the disease progresses one develops cirrhosis of the liver with fluid in the abdomen, jaundice etc.

With S. heamatobium infection one sees obstruction of the urinary system with blood in the urine and eventually bladder cancer.

S. japonicum can also spread to the central nervous system causing seizures.

Are there any lab tests to diagnose the illness?

One can demonstrate the eggs of Schistosoma parasites in biopsy of tissue or urine. Antibody tests are also available.

Is there any treatment?

Antibiotics called Praziquantel are effective.

What preventive measures can be taken?

Avoid wading, swimming or bathing in freshwater in endemic areas.

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