Retortamonas intestinalis

[Retortamonas intestinalis]

Causal Agents

Retortamonas intestinalis, a nonpathogenic flagellate.

Life Cycle

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

Geographic Distribution

Worldwide.

Clinical Presentation

Retortamonas intestinalis is considered nonpathogenic. The presence of trophozoites and/or cysts 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.

Retortamonas intestinalis, trophozoites.

Trophozoites of Retortamonas intestinalis are ovoid or pyriform and measure 4-10 µm long by 3-8 µm wide. The possess two flagella, one directed anteriorly and one extending posteriorly. A cytostome is present at the anterior half of the trophozoite and is bordered by a fibril. The single, spherical nucleus is located at the anterior end and contains a small karyosome and a fine layer of peripheral chromatin.

Figure A: Trophozoite of R. intestinalis in a stool specimen, stained with trichrome.

Figure B: Trophozoite of R. intestinalis in a stool specimen, stained with trichrome.

Retortamonas intestinalis, cysts.

Cysts of Retortamonas intestinalis are ovoid or pyriform and measure 4-7 µm long by 3-5 µm wide. Mature cysts contain a single nucleus, with a compact central karyosome and varying amounts of peripheral chromatin. The fibril associated with the cytostome may be been seen in close proximity to the nucleus.

Figure A: Cyst of R. intestinalis in a stool specimen, stained with trichrome.

Figure B: Cyst of R. intestinalis in a stool specimen, stained with trichrome.

Figure C: Cyst of R. intestinalis in a stool specimen, stained with trichrome.

Figure D: Cyst of R. intestinalis in a stool specimen, stained with trichrome.

Laboratory Diagnosis

Retortamonas intestinalis is identified through the detection of trophozoites and/or cysts 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.

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

Page last reviewed: May 3, 2016
Page last updated: May 3, 2016
Content source:
- Global Health – Division of Parasitic Diseases and Malaria
- Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site.
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- Global Health

DPDx - Laboratory Identification of Parasitic Diseases of Public Health Concern

Retortamonas intestinalis

Causal Agents

Life Cycle

Geographic Distribution

Clinical Presentation

Retortamonas intestinalis, trophozoites.

Retortamonas intestinalis, cysts.

Laboratory Diagnosis

Treatment Information

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Retortamonas intestinalis

Causal Agents

Life Cycle

Geographic Distribution

Clinical Presentation

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