Case #520 – July, 2020
A 67-year-old male from Houston, TX sought medical evaluation following 3 days of abdominal pain, diarrhea, and fatigue after returning from a two-week summer vacation in Nairobi, Kenya. Examination of a trichrome stained Zn-PVA stool smear submitted for routine ova and parasite (O&P) revealed objects shown in Figures A–D, ranging in size from 12-25μm. 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 polecki (Figures A and B) and blastocystosis caused by Blastocystis hominis (Figures C and D). Diagnostic morphologic features included:
- Trophozoites within the size range of E. polecki 10-25µm (Figures A and B).
- Large nucleus with evenly distributed peripheral chromatin and large central karyosome (Figures A and B).
- Vacuoles in cytoplasm (Figures A and B, blue arrow).
- Structures within the size range of B. hominis 5–40 µm (Figures C, D).
- Large central vacuole surrounded by several small nuclei (Figures C, D). Blastocystis hominis is a pleomorphic organism and the predominant form found in human stool specimens is referred to as the vacuolar (or central body) form.
Both E. polecki and B. hominis are considered non-pathogenic parasites. However, the pathogenicity of Blastocystis must be considered when found in large numbers in patients with abdominal symptoms who have no other plausible etiology.
 Figure A |
 Figure B |
More on amebiasis
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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.