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/.
[Endolimax nana] [Entamoeba coli] [Entamoeba gingivalis] [Entamoeba hartmanni] [Entamoeba polecki] [Iodamoeba buetschlii]
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.
Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii
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 . Both cysts and trophozoites of these species are passed in stool and considered diagnostic . 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 . Excystation occurs in the small intestine 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 . 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.
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 . 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 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).
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.
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.