Blastocystis Hominis Infection (Blastocystosis)

What is Blastocystis hominis infection?

Blastocystis hominis is a single-celled parasite that infects humans and some animals. Infection with Blastocystis hominis is called blastocystosis.

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.

Is Blastocystis harmful?

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:

• Subtypes: Some subtypes, which can be difficult to tell apart, may cause disease more than others.
• Lifecycle: Blastocystis changes shape during its lifecycle. Scientists think these shapes may vary in their disease-causing ability.
• Intestinal microorganisms: You naturally have different microorganisms in your intestines that are part of your immune system. The makeup of your intestinal tract is unique. Some people may be better equipped to resist Blastocystis infection than others.

How common is blastocystosis?

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.

How do people become infected with Blastocystis?

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.

What are the symptoms of blastocystosis?

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:

• Abdominal pain.
• Anal itching.
• Diarrhea.
• Gas and bloating.
• Nausea.
• Weight loss.

Does blastocystosis cause skin rash?

Blastocystosis is also associated with skin rashes and hives (urticaria). Hives are red, itchy welts on the skin that are often accompanied by swelling.

How is blastocystosis diagnosed?

If you have gastrointestinal symptoms, your healthcare provider will:

• Discuss your medical history, including your travel history and contact with animals.
• Perform a physical exam.
• Collect a stool sample for identification of Blastocystis under a microscope.

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.

How is blastocystosis treated?

The need to treat blastocystosis is unclear since its role in causing illness isn't fully understood.

Treatments healthcare providers use include:

• Antibiotics, such as metronidazole or cotrimoxazole, which combine the medications trimethoprim and sulfamethoxazole.
• Antiparasitic medications such as nitazoxanide.

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.

How can I prevent blastocystosis?

Steps you can take to prevent blastocystosis include:

• Avoid contaminated food or water. In countries where the water supply isn't safe, boil water before drinking it or using it to cook, or use bottled water.
• Wash and peel raw fruits and vegetables.
• Wash your hands after using the toilet, changing diapers and before eating or cooking.

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.

What is the prognosis for people with blastocystosis?

Many people with blastocystosis do not experience any symptoms. Those who develop gastrointestinal illness usually respond well to treatment.

When should I contact my healthcare provider?

Call your provider if you have a diarrheal illness that doesn’t go away or if you experience symptoms of dehydration, such as:

• Decreased production of urine or dark urine.
• Dizziness, sudden confusion or headache.
• Dry mouth or severe thirst.
• Fatigue.
• Irritability.

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.