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Case #322 - April, 2012

A 28-year-old man presented to his health care provider with intermittent diarrhea, mild abdominal cramping, and low-grade fever. Travel history included camping in the northwestern United States. Stool specimens were collected in formalin and polyvinyl alcohol (PVA) and sent to a commercial lab for ova-and-parasite (O&P) examination. Figures A and B show what was observed in moderate frequency on a trichrome-stained smear made from the PVA-preserved stool. The objects of interest measured 12-15 micrometers on average in length. The images were captured at 1000x magnification. What is your diagnosis? Based on what criteria?


Figure A


Figure B

Case Answer

This case showed the nonpathogenic flagellate, Pentatrichomonas hominis. Diagnostic features shown included:

  • trophozoites within the size range for P. hominis (6-20 micrometers long).
  • trophozoites containing a single nucleus with a small karyosome and a posteriorly-directed axostyle.
  • presence of flagella; although P. hominis has five flagella, few, if any, are generally seen on stained smears.

More on: Pentatrichomonas hominis

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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