Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at November 30, 2016

Schistosomiasis, sometimes referred to as bilharzia, is a parasitic infection typically found in poor areas without adequate sanitation and in tropical and sub-tropical climates. The disease affects between 200 and 240 million people worldwide and can lead to chronic ill health. Schistosomiasis does not occur in the United States, but it can be contracted by individuals who travel to areas where the parasite is prevalent. 


Definition & Facts

The parasitic worm that causes schistosomiasis lives in certain freshwater snails. The infectious form of the worm, called cercariae, emerges from the snail and contaminates the water where the snail lives. These parasites can live in the water for up to 48 hours. Humans become infected when their skin comes into contact with the contaminated water.

The Schistosoma haematobium, S. mansoni, and S. japonicum parasites are responsible for the majority of human infections. These parasites are commonly found in parts of Asia, the Middle East, South America, the Caribbean, and throughout Africa. Schistosomiasis is the second-most devastating parasitic disease in terms of impact after malaria

Symptoms & Complaints

The symptoms of schistosomiasis may not develop for several weeks or months. Some patients notice small, red, itchy bumps at the site where the worms burrowed into the skin.

After several weeks, an infected person may develop a general feeling of being unwell along with diarrhea, abdominal pain, a cough, joint aches, and muscle aches.

These symptoms are caused by the body’s reaction to the eggs that the worms produce and not the worms themselves. These acute symptoms may eventually subside after a few weeks; however, patients should still seek treatment to avoid chronic schistosomiasis and long-term complications, including the following:

Although rare, the eggs can also travel to the brain and spinal cord where they can cause paralysis, seizures, and spinal cord inflammation. Children who experience repeated schistosomiasis infection can also develop malnutrition and learning disabilities.


Schistosomiasis is transmitted when an infected person urinates or defecates in a fresh water source, such as a pond, river, lake, canal, or reservoir. The urine and feces contain Schistosoma eggs that subsequently hatch, and if certain species of snail are present, the parasites will develop and grow inside the snail. Once developed, the parasites leave the host snail and can survive in the water for a couple of days.

A person who uses the contaminated water for bathing, swimming, wading, or washing can become infected when the parasite penetrates their skin. Worms eventually develop within the body’s blood vessels that produce more eggs. The eggs travel to the intestines and bladder where they are then passed through the urine and stool, which starts the cycle over again.

It is not possible to contract schistosomiasis by direct person-to-person contact. The larvae of the worm must develop inside the freshwater snail for several weeks before they are able to infect another person. Anyone who lives or has traveled to areas where the parasite is found and has had contact with untreated water is at risk for developing schistosomiasis. 

Diagnosis & Tests

Anyone who has traveled to a part of the world where schistosomiasis is prevalent and who has been in contact with untreated water should see their doctor if they develop symptoms of the disease. The doctor may request a urine or stool sample to check for the presence of eggs. The Centers for Disease Control and Prevention have also developed a blood test for schistosomiasis. For best results, it should be performed at least six to eight weeks after the last exposure to contaminated water. 

Treatment & Therapy

Praziquantel is the treatment for schistosomiasis infections regardless of the species of the parasite. Timing is a significant factor in the success of the treatment. The best results are achieved when praziquantel is given six to eight weeks after the patient’s last exposure to contaminated water. That is because the medication is most effective against the adult worm and after the body has developed a mature antibody response to the parasite.

For most patients, a single course of treatment is enough to cure the infection; however, a light infection may limit the response to the treatment, and a second course of praziquantel may be required in two to four weeks to ensure that the infection is cured. There is limited evidence that some of the parasites may be resistant to praziquantel based on low cure rates among certain populations; however, the drug remains the preferred treatment since this has not been confirmed by widespread studies.

The World Health Organization recommends praziquantel treatment for pregnant women and advises that evidence suggests that the treatment is safe for children as young as one year old. Since the drug is most often available in large pills, it can pose a choking hazard and create swallowing difficulties for young children. 

Prevention & Prophylaxis

Schistosomiasis is generally easily prevented by following these measures:

  • Do not swim, wade, or bath in fresh water when visiting countries where the disease is known to occur. Swimming in chlorinated or salt water is not believed to create a risk of developing schistosomiasis. 
  • Do not drink water directly from a canal, river, stream, spring, or lake even when it appears clean.
  • While iodine treatments may be effective in killing some bacteria and parasites, they do not kill everything. Water should be filtered or boiled for at least 1 minute before drinking to kill any parasites, viruses, or bacteria. 
  • Water that has been stored in a tank for at least 48 hours should be safe for showering. Otherwise, water should be heated to at least 150°F for 5 minutes before bathing. 
  • If the water exposure was very brief, drying vigorously with a towel may prevent the parasite from penetrating the skin. Towel drying should not be relied on as a primary means of preventing schistosomiasis. 

Individuals who come into contact with contaminated water while traveling and believe they may be infected with schistosomiasis should see their doctor after returning home for possible testing.