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Case #488 - March, 2019

Fecal specimens were collected from a refugee population as part of a screening program. Specimens were collected fresh for a direct smear examination and in polyvinyl alcohol (PVA) from which smears were prepared and stained with trichrome stain. Figures AD show what was detected in one of the specimens using 1000x oil magnification; objects of interest measured 14-20 micrometers on average. Figure D is of the same objects at two different focal planes. What is your diagnosis? Based on what criteria?

parasitic image

Figure A

parasitic image

Figure B

parasitic image

Figure C

parasitic image

Figure D

The objects/organisms detected were trophozoites and cysts of Entamoeba polecki, a commensal amoeba. Morphologic features shown included:

  • uninucleate trophozoites (Figures A and B) within the size range (10-25 micrometers) for the species with a large, irregular nucleus with a pleomorphic karyosome, which may be central or eccentric within the nucleus
  • vacuolated cytoplasm visible in some trophozoites (Figure B) as well as blunt pseudopodia (Figures A and B)
  • uninucleate cysts within the size range (9-25 micrometers) for the species containing numerous irregularly shaped, red-staining chromatoid bodies (Figures CD)

The presence of E. polecki, as with other commensal protozoa, can be an indicator of fecal contamination of a food or water source and does not rule out other parasitic infections.

More on E. polecki  https://www.cdc.gov/dpdx/intestinalamebae/index.html

Images presented in the monthly 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: April 18, 2019