Schistosomiasis

Overview

What is schistosomiasis?

Schistosomiasis is an infection caused by trematodes (flukes). These schistosomes (also called blood flukes) are parasitic flatworms that belong to the genus Schistosoma. Parasites are creatures who live in or on another organism (host) and get their food from the host. This has a negative effect on the host.

In the case of schistosomiasis, the flukes are found in snails and then are shed into the water. If your skin comes in contact with contaminated water, the parasites can move into you and live there for years. The form of the parasite that infects humans after developing in the snail has a kind of forked head that allows it to penetrate your skin.

The three main types of schistosomes are responsible for the two main forms of the condition: urogenital schistosomiasis and intestinal schistosomiasis.

This condition is also known as bilharzia or snail fever.

Who does this condition affect?

Anyone can be infected by these parasites by swimming or bathing in contaminated water. The parasite is found in freshwater lakes, rivers and ponds in the following areas:

  • Many parts of Africa, including sub-Saharan Africa and southern Africa. The worms are also found in Maghreb, a region of North Africa, and the Nile River valley in Egypt and Sudan.
  • Brazil, Surinam and Venezuela (South America).
  • Dominican Republic, Guadeloupe, Martinique (the Caribbean). The risk in the Caribbean is low.
  • The southern part of China.
  • Areas in Southeast Asia and the Philippines and in Laos and Cambodia.
  • Corsica.

How common is schistosomiasis?

It’s estimated that over 230 million people worldwide have this type of infection. Even though the parasite that causes this disease isn’t found in the U.S., you can get it if you travel to places that do have the parasite.

Symptoms and Causes

What are the symptoms of schistosomiasis?

Many people have no symptoms of schistosomiasis. Early signs and symptoms (those that happen within days of being infected) may include itchiness and a skin rash.

Later symptoms (those that develop within 30 to 60 days of being infected) may include:

If you aren’t treated, symptoms that develop after years of being infected may include:

Chronic (long-lasting) schistosomiasis may make it more likely that you’ll develop scars on your liver or bladder cancer.

In rare cases, you might have eggs in your brain or spinal cord. If this is true, you may have seizures, become paralyzed or have an inflamed spinal cord.

What causes the condition?

Schistosomiasis is caused by a parasite that resides in certain snails in freshwater locations. The form of the parasite that leaves the snail penetrates human skin with its forked head. Infected people release urine and feces that are infected with eggs into water where the snails are. The eggs move into the snails and the cycle goes on. Infected children and adults get infected over and over again.

However, people don’t infect each other. You can’t give schistosomiasis to another person if you have it.

Researchers are working to find a way to control the disease, with some efforts directed toward vaccine development and others toward finding a way to deal with the snails.

Diagnosis and Tests

How is schistosomiasis diagnosed?

Sometimes eggs can be found in urine or stool samples, but often a blood test is needed. All of these are examined under a microscope.

Management and Treatment

What medications/treatments are used?

Schistosomiasis is treated with the prescription medication praziquantel (Biltricide®). The drug, provided in pill form, belongs to a class of medications called anthelmintics. These types of drugs kill worms.

You should take praziquantel with water and food. It's usually taken for one day, either as a single larger dose, or three smaller doses in one day.

Before taking any medication, you should tell your healthcare provider what other medications and supplements you take and what kinds of allergies you have. You should also ask whether or not you’ll be able to eat grapefruit or drink grapefruit juice while taking this medication.

Complications/side effects of the treatment

You may have side effects from the infection itself or from the medication and the worms dying off, or both. These might include:

  • Headache.
  • Fever.
  • Stomach pain or nausea.
  • Dizziness.
  • Itching.
  • Malaise (just not feeling well).

If you have hives, contact your healthcare provider. Also, call your provider about any other symptoms that worry you or that seem to be getting worse.

Prevention

How can I reduce my risk?

There are things you shouldn’t do in water from fresh pools or lakes or rivers in areas that are known to have the snails and parasites that cause schistosomiasis.

  • Don’t assume that the water is safe just because people tell you it’s OK. It’s better to not take the chance in areas where the parasite is known to exist.
  • Don’t drink from these bodies of water. It’s not that you’ll get the parasites from drinking the water, but they can enter your skin around your mouth.
  • Don’t bathe or swim in these waters.
  • Don’t wash clothes in these waters.
  • Don’t fish in these bodies of water.

If you do get wet, you can use a towel to dry yourself off with vigorous motions. That may help, but you shouldn’t rely on it.

Outlook / Prognosis

What can I expect if I have this condition?

If you are treated, you can expect to be cured. If you live in a location where these parasites are active, you’ll need to take care to avoid freshwater bodies of water that may be infected. You can be infected again. There’s no vaccine to prevent infection.

If you aren’t treated, you can stay infected. This could cause serious problems with your liver, intestines and bladder. Women can develop urogenital schistosomiasis, a condition that could increase the risk of developing HIV because the tissue is damaged. The condition is also linked to bladder cancer.

Children who are infected over and over again could develop anemia and might not grow properly. Without treatment, schistosomiasis can be fatal.

Living With

When should I see my healthcare provider?

If you live in, work in or travel to areas where schistosomiasis is known to be a problem, and you have any itching, fever or urinary symptoms, you should contact your healthcare provider. If you came into contact with any water that you suspect might have been contaminated, contact your provider.

A note from Cleveland Clinic

While schistosomiasis isn’t prevalent in the U.S., you can become contaminated if you come into contact with infected water while outside of the country. It’s probably a good idea to get checked when you get home even if you don’t have symptoms. Many people don’t have symptoms in the beginning. If you do have the parasite, you can and should be treated.

Last reviewed by a Cleveland Clinic medical professional on 03/23/2022.

References

  • Centers for Disease Control and Prevention. Multiple pages reviewed for this article. Schistosomiasis (https://www.cdc.gov/parasites/schistosomiasis/) Accessed 3/23/2022.
  • Colley DG, Bustinduy AL, Secor WE, King CH. Human schistosomiasis. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4672382/) Lancet. 2014;383(9936):2253-2264. doi:10.1016/S0140-6736(13)61949-2 Accessed 3/23/2022
  • Lackey EK, Horrall S. Schistosomiasis. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554434/ (https://www.ncbi.nlm.nih.gov/books/NBK554434/) Accessed 3/23/2022.
  • National Institute of Allergy and Infectious Diseases. Schistosomiasis (Bilharzia). (https://www.niaid.nih.gov/diseases-conditions/schistosomiasis-bilharzia) Accessed 3/23/2022.

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