Blastocystis is a single-celled parasite that can live in your intestines. Many people have no symptoms. Others develop gastrointestinal illness, but it is unknown whether Blastocystis is the cause. Antibiotic or antiparasitic medications usually resolve symptoms.
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Blastocystis hominis is a single-celled parasite that infects humans and some animals. Infection with Blastocystis hominis is called blastocystosis.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Blastocystis hominis was the original name of the organism found in humans. Later studies found that there are many different strains (subtypes) of Blastocystis and they vary widely from one another. Blastocystis has at least 22 subtypes, nine of which can infect humans. Scientists now call this group of parasites Blastocystis species.
Scientists discovered Blastocystis in the early 1900s, but don’t fully understand if it causes disease. It can live in the digestive tract of healthy people without causing symptoms. In some people, it may cause gastrointestinal illness.
Confusion over whether Blastocystis causes disease may be due to:
Blastocystosis is common throughout the world. But healthcare providers aren't sure how widespread it is because many people don't know they have it. In general, it is more common in developing countries.
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Blastocystosis is contagious and spreads through infected human or animal feces. People become infected through poor handwashing, especially if they work with animals or are in a daycare environment. Ingestion of contaminated food or water is also a common cause of infection.
Blastocystosis is associated with inflammation in the digestive tract (enteritis). However, it is unclear if Blastocystis causes gastrointestinal illness or if its presence in the digestive tract is coincidental. Symptoms can include:
Blastocystosis is also associated with skin rashes and hives (urticaria). Hives are red, itchy welts on the skin that are often accompanied by swelling.
If you have gastrointestinal symptoms, your healthcare provider will:
Other tests can help detect Blastocystis and its subtypes but are usually only available in research settings. Even if you have blastocystosis, your provider will also look for other organisms that may be causing your symptoms.
The need to treat blastocystosis is unclear since its role in causing illness isn't fully understood.
Treatments healthcare providers use include:
These medications often resolve symptoms but they aren't always effective. Variable treatment success may be due to antibiotic resistance or variability between the different strains of Blastocystis. Alternatively, symptoms may be caused by another organism.
Natural treatments, special diets and herbal supplements for blastocystosis are also available. The effectiveness of these treatments has not been well studied. Talk to your healthcare provider before using these treatments to make sure they are safe.
Steps you can take to prevent blastocystosis include:
Research studies show that maintaining a healthy digestive tract may also help. Probiotics are healthy bacteria that help support your digestive and immune systems. Increasing your intake of probiotic-containing foods or taking probiotic supplements may help prevent Blastocystis from living in your intestines.
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Many people with blastocystosis do not experience any symptoms. Those who develop gastrointestinal illness usually respond well to treatment.
Call your provider if you have a diarrheal illness that doesn’t go away or if you experience symptoms of dehydration, such as:
A note from Cleveland Clinic
Researchers are working to understand Blastocystis and whether it causes disease in humans. You can prevent gastrointestinal illnesses by washing your hands frequently and avoiding contaminated food and water. If you do develop persistent diarrhea or other gastrointestinal symptoms, your provider will evaluate you based on your symptoms, diagnostic tests and medical and travel history. Talk to your healthcare provider about the possible cause of your illness and the best treatment approach to help you feel better.
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Last reviewed on 05/04/2022.
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