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DPDx

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/nonpathprotozoa/.

Intestinal Amebae

[Endolimax nana] [Entamoeba coli] [Entamoeba gingivalis] [Entamoeba hartmanni] [Entamoeba polecki] [Iodamoeba buetschlii]

Cyst of Entamoeba coli in an unstained wet mount. Note the presence of more than four nuclei.]

Cyst of Entamoeba coli in an unstained wet mount. Note the presence of more than four nuclei.


Trophozoite of Endolimax nana stained with trichrome.

Trophozoite of Endolimax nana stained with trichrome.


Cyst of Iodamoeba buetschlii stained with trichrome. Note the glycogen vacuole (arrow).

Cyst of Iodamoeba buetschlii stained with trichrome. Note the glycogen vacuole (arrow).

Causal Agent

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic and reside in the large intestine of the human host. Entamoeba gingivalis is also considered nonpathogenic and resides in the oral cavity of the human host, in the gingival pockets at the base of the teeth.


Life Cycles

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii

Life cycle of nonpathogenic intestinal amebae.

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic and reside in the large intestine of the human host The letter A. Both cysts and trophozoites of these species are passed in stool and considered diagnostic The number 1. Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool. Colonization of the nonpathogenic amebae occurs after ingestion of mature cysts in fecally-contaminated food, water, or fomites The number 2. Excystation occurs in the small intestine The number 3 and trophozoites are released, which migrate to the large intestine. The trophozoites multiply by binary fission and produce cysts, and both stages are passed in the feces The number 1. Because of the protection conferred by their cell walls, the cysts can survive days to weeks in the external environment and are responsible for transmission. Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.

Entamoeba gingivalis

Life cycle of Entamoeba gingivalis.

There is no known cyst stage for Entamoeba gingivalis; trophozoites live in the oral cavity of humans, residing in the gingival pockets near the base of the teeth The letter A. They are not considered pathogenic, and feed on bacteria and other debris. Trophozoites are transmitted person-to-person orally by kissing or fomites (such as eating utensils) The number 1. The trophozoite stage of E. gingivalis is morphologically similar to that of E. histolytica, and the two should be differentiated, as both can be coughed up in sputum specimens (for the latter, when present in pulmonary abscesses).

Geographic Distribution

All six species are distributed worldwide. Entamoeba polecki in nature is primarily a parasite of pigs and monkeys, and human infection is more prevalent in areas where the people have animal contact.

Clinical Presentation

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic, although they have been found in the stool of patients presenting with diarrhea where no known pathogens were identified. Their presence in stool can be an indicator of fecal contamination of a food or water source, and does not rule-out the presence of other parasites. Entamoeba gingivalis is also considered nonpathogenic, but is found in about 95% of patients with gum disease and about 50% of patients with healthy gums.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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