Causes

Blastocystis is a microscopic single-celled organism (protozoan). Many parasitic protozoans normally live in your digestive tract and are harmless or even helpful; others cause disease.

It's not clear whether blastocystis causes disease. Most people who carry the organism have no signs or symptoms, but it's also found in people who have diarrhea and other digestive problems.

Explanations for this variability include:

• Some types of blastocystis may be more likely to cause disease than others.
• Some people may be more vulnerable to blastocystis infection.
• Disease may be caused by other organisms that coexist with Blastocystis.

Blastocystis can be passed between people and from animals to people. Transmission may be from:

• Contaminated food or water
• Exposure to human or animal feces