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

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.