Overview
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.
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