Case #276 – May, 2010

The DPDx Team received stained stool smears from the Vermont Department of Health Laboratory for Entamoeba identification. The patient was a 12-year-old refugee from Myanmar who had also traveled to Malaysia. The patient’s stool had been collected in sodium acetate-acetic acid-formalin (SAF) and sent to the state laboratory for processing. Figures A–F show what was observed at 1000x magnification on a smear stained with iron hematoxylin. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

Figure E

Figure F

This case presented a mix of three species of protozoa generally considered nonpathogenic: Entamoeba hartmanni (Figures B, C, and E), Endolimax nana (Figures D and F), and Pentatrichomonas hominis (Figure A). Diagnostic morphologic features included:

a trophozoite of P. hominis containing a single nucleus with a small karyosome and a posteriorly-directed axostyle (Figure A). The trophozoite was also within the size range for P. hominis (6-20 micrometers long).
a trophozoite of E. hartmanni containing a single nucleus with a small, central karyosome and evenly-distributed peripheral chromatin (Figure B). The trophozoite was also within the size range for E. hartmanni (5-15 micrometers).
cysts of E. hartmanni containing a nucleus (within the focal plane) with a small, central karyosome and evenly-distributed peripheral chromatin (Figures C and E). The cysts were also in the size range for E. hartmanni (5-10 micrometers in diameter).
trophozoites of E. nana containing a nucleus with a large karyosome and no peripheral chromatin (Figures D and F). The trophozoites were also within the size range for E. nana (6-12 micrometers).

Although these three species are generally considered nonpathogenic, they should be reported in all routine ova-and-parasite (O&P) examinations. Their presence in stool could indicate fecal contamination of a food or water source and does not rule-out the presence of a true pathogen.

More on: Pentatrichomonas hominis: Endolimax nana and Entamoeba hartmanni

This case, and the specimen from which images were taken, are courtesy of the Vermont Department of Health Laboratory.

Images presented in the DPDx case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.

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

Page last reviewed: August 24, 2016

Content source: Global Health, Division of Parasitic Diseases and Malaria