Case #296 – March, 2011

A 30-year-old man presented to his primary care provider with abdominal pain, fatigue, and diarrhea (sometimes tinged with blood). The patient had recently returned after two weeks in Armenia. A stool specimen was collected in both 10% formalin and poly-vinyl alcohol (PVA) for routine ova-and-parasite (O&P) examination. A smear was prepared from the PVA-preserved specimen and stained with trichrome. Figures A–D show what was observed in moderate numbers on the smear at 1000x magnification. The objects of interest measured on average 25 micrometers in length. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

This was a case of amebiasis caused by Entamoeba histolytica. Morphologic features shown included:

trophozoites showing ingested red blood cells.
nuclei showing evenly distributed peripheral chromatin and a centrally-located karyosome.
some trophozoites showing progressive pseudopods.

If ingested red blood cells are observed, a species-level identification of E. histolytica may be given. Specimens presenting with these morphologic features, but without ingested RBCs, should be reported as E. histolytica/dispar and further testing such as PCR should be performed.