Case #243 – January, 2009

A ten-year-old child returned from summer camp with abdominal discomfort, nausea and diarrhea. He was taken to his pediatrician and a stool specimen was collected for routine work-up, including ova and parasite (O&P) examination. Figures A–D show what was observed on a trichrome-stained slide prepared from a PVA-preserved aliquot of the stool. The objects in Figures A and B measured approximately 11 micrometers; the objects in Figures C and D measured approximately seven micrometers. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

These images showed the trophozoites and cysts of the nonpathogenic ameba, Iodamoeba buetschlii. Diagnostic features included:

trophozoites (Figures A and B) within the size range (8-20 micrometers) for the species, containing a single nucleus with a large karyosome and no peripheral chromatin.
cysts (Figures C and D) within the size range (5-20 micrometers) for the species, containing a single nucleus with a large, eccentric karyosome and a large glycogen vacuole.

Although I. buetschlii is considered non-pathogenic, it should be reported in all stool parasite work-ups, as its presence may indicate fecal contamination of a food or water source.