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BackFact Sheet

Nonpathogenic (Harmless) Intestinal Protozoa

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What are nonpathogenic intestinal protozoa?

They are single-celled parasites that are commonly found in the intestines but never cause illness. They do not harm the body, even in people with weak immune systems.


The nonpathogenic intestinal protozoa include:

  • Chilomastix mesnili (KYE-low-MASS-ticks mez-KNEE-lye)
  • Endolimax nana (En-doe-LYE-max NAH-na)
  • Entamoeba coli (ENT-a-ME-ba KO-lye)
  • Entamoeba dispar (ENT-a-ME-ba DIS-par)
  • Entamoeba hartmanni (ENT-a-ME-ba hart-MAHN-ee)
  • Iodamoeba buetschlii (eye-ODE-a-ME-ba bush-lee-eye)

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Where are these protozoa found in the body?

They are found only in the lumen (cavity) of the intestinal tract. They are not found in the cells that line the intestines, and they do not spread to other parts of the body.

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How are these protozoa detected?

By microscopic examination of stool specimens.

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I was told that my stool tested positive. How do people get these protozoa?

By swallowing them, for example, by ingesting food or water that is contaminated with feces. This is called fecal-oral transmission. The presence of nonpathogenic protozoa in your stool simply indicates that you had a fecal exposure sometime in the past.

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I have not been feeling well. Could these protozoa be causing my symptoms?

No. These nonpathogenic protozoa do not cause illness. Other possible causes of your symptoms should be considered. To see whether you became infected with a pathogen, your health care provider might want to check your stool for bacteria, viruses, and other parasites. Another possibility is that your symptoms are not caused by an infection.

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How long could these protozoa stay in my intestines?

For weeks, months, or years.

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To be on the safe side, should I be treated to get them out of my intestines?

No. These protozoa are harmless.

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This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.



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This page last reviewed February 7, 2008

Centers for Disease Control and Prevention
National Center for Infectious Diseases
Division of Parasitic Diseases