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Case #320 - March, 2012

Stool specimens were collected from Haitian refugees as part of a screening program for intestinal parasites. Stool was collected in polyvinyl alcohol (PVA) and 10% formalin and sent to the county public health lab for routine ova-and-parasite (O&P) examination. Figures A-D show what was observed in moderate numbers from one of the patients on a trichrome-stained slide from the PVA-preserved stool. All images were captured at 1000x magnification. What is your diagnosis? Based on what criteria?


Figure A


Figure B


Figure C


Figure D

Case Answer

This case showed a mix of two intestinal protozoa, Endolimax nana and Blastocystis hominis. Both species were shown in all four images. Diagnostic features included:

  • ovoid cysts of E. nana presenting with 2-4 nuclei, each with a discrete karyosome (Figures A-C; there was also a cyst out-of-focus in the upper edge of Figure D).
  • trophozoite of E. nana presenting with a single nucleus containing a large, central karyosome and no peripheral chromatin (Figure D).
  • cyst-like bodies of B. hominis presenting with a large, central body surrounded by a narrow rim of cytoplasm containing nuclei and inclusion bodies (Figures A-D).

More on: Blastocystis hominis; Endolimax nana

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.

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  • Page last reviewed: August 24, 2016
  • Page last updated: August 24, 2016
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