Schistosomiasis is caused by a parasitic flatworm that enters your skin from infected bodies of water. It is associated with bladder cancer. There is no vaccine, but there is a drug to treat it.
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.
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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:
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.
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.
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.
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.
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.
You may have side effects from the infection itself or from the medication and the worms dying off, or both. These might include:
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.
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.
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.
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.
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.
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