About Schistosomiasis

Key points

  • Schistosomiasis is a disease caused by parasitic worms.
  • The parasites that cause schistosomiasis live in certain types of freshwater snails.
  • Schistosomiasis spreads when you come into contact with unsafe water that contains these snails.


Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. More than 200 million people worldwide are infected. Schistosomiasis is one of the neglected tropical diseases (NTDs). It is the second most dangerous parasitic disease after malaria. The parasites that cause schistosomiasis live in certain types of freshwater snails. Although schistosomes are in the United States, they are not the species that infect people.

The infectious form of the parasite, called cercariae, comes out of the snail into the water. You can become infected if your skin comes in contact with unsafe freshwater.

Most human infections are caused by these species:

  • Schistosoma mansoni
  • S. haematobium
  • S. japonicum

Less common infections are caused by these species:

  • S. mekongi
  • S. intercalatum

Signs and symptoms

Most people have no symptoms at the early phase of infection. Some have a rash or itchy skin in the first few days.

Within 1 – 2 months of infection, symptoms may include:

  • Fever
  • Chills
  • Cough
  • Muscle aches

Repeated infections in children can cause:

  • Anemia (lack of red blood cells)
  • Malnutrition (lack of nutrients)
  • Learning difficulties

You can also develop chronic (long-term) symptoms if you do not treat the infection. The eggs cause inflammation or scarring when traveling to the intestine, liver, or bladder.

If you think you have schistosomiasis, see your healthcare provider.

Let them know:

  • If and where you've traveled recently
  • How long you were there
  • If you may have touched unsafe water

Exposure risks

You might get schistosomiasis if your skin touches freshwater from canals, rivers, streams, ponds, or lakes in places where it is common. Please refer to WHO's map on where schistosomiasis currently spreads.


  • Southern and sub-Saharan Africa (high risk)
  • North Africa's Maghreb region
  • Egypt and Sudan's Nile River valley


  • Southern China
  • Southeast Asia
    • Cambodia
    • Indonesia
    • Laos
    • Philippines


  • Corsica (ongoing transmission or spread)

The Americas

  • South America
    • Brazil
    • Suriname
    • Venezuela
  • Caribbean (low risk)
    • Antigua & Barbuda
    • Dominican Republic
    • Guadeloupe
    • Martinique
    • Montserrat
    • Puerto Rico
    • Saint Lucia

The Middle East

  • Iran
  • Iraq
  • Saudi Arabia
  • Yemen
Keep Reading: Schistosomiasis Facts

How it spreads

Schistosomiasis spreads in six steps:

  1. Schistosoma eggs enter freshwater when people with schistosomiasis urinate (pee) or defecate (poop) in the water.
  2. The eggs hatch, infect a specific type of freshwater snail, develop, and multiply inside the snails.
  3. The Schistosoma parasite leaves the snail and enters the water, where it can live for about 48 hours.
  4. The parasite enters the skin of people who are in contact with unsafe water.
  5. Within weeks, the parasites turn into adult worms in the blood vessels of the body.
  6. The female worms produce eggs that travel to the bladder or intestine and come out in urine or stool (poop).


The most effective ways to prevent schistosomiasis include:

  • Do not get into or touch unsafe freshwater.
  • Drink safe water.
  • Water for bathing
    • Boil you bath water.
    • Add 1 mg of chlorine per liter of water and let sit for 30 minutes.
    • Let water sit for 24 hours before bathing.


Your health care provider may take a stool or urine sample to see if you have the parasite. They can also use a blood sample to test for infection. You should wait 6 – 8 weeks to give samples after contacting unsafe water. This window of time helps with accuracy.

Treatment and recovery

Safe and effective drugs are available for treating schistosomiasis. Praziquantel is the recommended treatment drug. See your healthcare provider for diagnosis and treatment.