Case #228 – May, 2008

Within a week of returning from a conference in Mexico, a 28-year-old woman presented to her primary care physician with cramps, abdominal pain, gas and diarrhea. A routine Ova and Parasite (O&P) examination was performed on stool specimens. Figures A–F show objects observed on a trichrome-stained slide prepared from the stool. All images were taken at 1000x oil magnification. The objects in Figures A–C measured 12 micrometers. The objects in Figures D and E averaged 10 micrometers. The object in Figure F measured 12 micrometers in diameter. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

Figure E

Figure F

This was a case of giardiasis caused by Giardia duodenalis (Figures B and C). Also observed were Entamoeba polecki (Figures A and B), Dientamoeba fragilis (Figures D and E) and Blastocystis hominis (Figure F). Although the pathogenic status of E. polecki, B. hominis and D. fragilis is currently unresolved, but they should be reported in all routine O&P examinations. The diagnostic features for each organism included:

Giardia duodenalis:

ovoid cysts within the size range (8-19 micrometers) for the species.
the presence of median bodies, fibrils and nuclei.

Entamoeba polecki:

cysts within the size range (9-24 micrometers) for the species.
the presence of a large, irregular nucleus with a pleomorphic karyosome.
the presence of numerous irregular, red-staining chromatoid bodies.

Dientamoeba fragilis:

trophozoites within the size range (5-15 micrometers) for the species.
a pair of nuclei made up of clusters of karyosomal granules.

Blastocystis hominis:

a cyst-like form within the size range (5-40 micrometers) for the species.
a large green-stained central body, surrounded by a thin ring of cytoplasm containing several red-stained inclusion bodies.

More on: Giardiasis; Blastocystis hominis; Dientamoeba fragilis; Entamoeba polecki

Images presented in the DPDx case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.