Bilharzia (schistosomiasis), named after Theodor Biharz who identified it in 1851, today affects more than 200 million people in tropical countries. It is caused by a minute parasite that spends part of its life cycle in freshwater snails (1) and part in water when it can penetrate the skin of anyone washing or bathing (2). The invading parasite lays up to 40,000 eggs after developing into an adult. These interfere with blood flow and damage liver, lungs, and kidneys.

Bilharzia is a chronic parasitic disease of the bladder, intestine, or liver. You become infected when your skin comes in contact with contaminated freshwater in which certain types of snails that carry schistosomes (a type of parasitic worm) are living. Bilharzia, also called schistosomiasis, is not found in the United States and Europe, but more than 200 million people are infected worldwide.


Freshwater becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and if certain types of snails are present in the water, the parasites grow and develop inside the snails. The parasite leaves the snail and enters the water where it can survive for about 48 hours. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing, or washing in contaminated water. Within several weeks, worms grow inside the blood vessels of the body and produce eggs. Some of these eggs travel to the bladder or intestines and are passed into the urine or stool.



Within days after becoming infected, you may develop a rash or itchy skin. Fever, chills, cough, and muscle aches can begin within 1-2 months of infection. Most people have no symptoms at this early phase of infection.


Eggs travel to the liver or pass into the intestine or bladder, causing inflammation or scarring. Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of infection, the parasite can also damage the liver, intestines, lungs, and bladder. Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, or spinal cord inflammation.


Symptoms of schistosomiasis are caused by the body's reaction to the eggs produced by worms, not by the worms themselves.



If you think you have bilharzia, see your health care provider. If you have traveled to countries where bilharzia is found and had contact with freshwater, describe in detail where and for how long you traveled. Explain that you may have been exposed to contaminated water.


Your health care provider may ask you to provide stool or urine samples to see if you have the parasite. A blood test has been developed and is available at CDC. For accurate results, you must wait 6–8 weeks after your last exposure to contaminated water before the blood sample is taken.



Safe and effective drugs are available for the treatment of schistosomiasis. You will be given pills to take for 1-2 days.



Bilharzia occurs the following regions:


  • Africa: all freshwater in southern and sub-Saharan Africa – including the great lakes and rivers as well as smaller bodies of water – is considered to be at risk for schistosomiasis transmission. Transmission also occurs in the Nile River valley in Egypt.
  • South America: including Brazil, Suriname, Venezuela
  • Caribbean: Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (risk is low)
  • The Middle East: Iran, Iraq, Saudi Arabia, Yemen
  • Southern China
  • Southeast Asia: Philippines, Laos, Cambodia, central Indonesia, Mekong delta