Enteromonas hominis

[Enteromonas hominis]

Causal Agents

Enteromonas hominis, a nonpathogenic flagellate.

Life Cycle


Both cysts and trophozoites of Enteromonas hominis are shed in feces The number 1. Infection occurs after the ingestion of cysts in fecal-contaminated food or water, or on fomites The number 2. In the large (and possibly small) intestine, excystation releases trophozoites. Enteromonas resides in the large intestine, where it is regarded as a commensal and is not known to cause disease.

Geographic Distribution


Clinical Presentation

Enteromonas hominis is considered nonpathogenic. The presence of cysts and/or trophozoites in stool specimens can however be an indicator of fecal contamination of a food or water source, and thus does not rule-out other parasitic infections.

Enteromonas hominis cysts.


Cysts of Enteromonas hominis are ellipsoidal, measuring 4-8 &m long by 3-5 &m wide. Cysts may contain one, two or four nuclei, with binucleate forms being the most common. In binucleate forms, the nuclei are often at opposite polar ends of the cyst; in forms with four nuclei, they are often paired at opposite ends. Nuclei possess a large, central karyosome, often surrounded by a clear area, and do not contain peripheral chromatin.
Figure A: Cyst of E. hominis, possessing four nuclei, in a stool specimen stained with iron-hematoxylin.
Figure B: Cyst of E. hominis, possessing four nuclei, in a stool specimen stained with iron-hematoxylin.

Laboratory Diagnosis

Enteromonas hominis is identified through the detection of cysts and/or trophozoites in stool specimens. Identification is best accomplished by direct wet mounts that reveal the characteristic, jerky movement of the organisms. They may also be identified in permanent stained smears, although their affinities for stain are inconsistent and with their small size are often overlooked.

Diagnostic Findings

More on: Morphologic comparison with other intestinal parasites.

Treatment Information

For information about treatment please contact CDC-INFO.

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