Case #361 – December 2013

A 27-year-old man in the U.S. Army, who had been stationed overseas in southeast Asia, sought medical attention for nausea, vomiting, and intermittent diarrhea. A stool specimen was collected in 10% formalin for Ova and Parasites (O&P) testing. A formalin-ethyl acetate (FEA) concentration was performed and a wet mount examined using 1000x magnification. Figures A-E show what was observed in few numbers. The objects in Figures A–C measured 18 micrometers on average; objects in Figures D and E measured 8.0 micrometers on average. Figures B and C shows two different focal planes of the same object. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

Figure E

Figure A showed a trophozoite of Entamoeba coli; Figures B and C showed a cyst of E. coli. Figures D and E showed cysts of Chilomastix mesnili. Diagnostic morphologic features included:

a trophozoite with irregular peripheral chromatin and within the size range for E. coli.
a mature cyst with more than 4 nuclei that also exhibited irregular peripheral chromatin and was within the size range for E. coli.
pyriform cysts that were within the size range for C. mesnili exhibiting a cytostome and a large nucleus.

Both of these organisms are considered nonpathogenic and can reside in the large intestine. While neither species is regarded as a pathogen, their presence in stool can be indicative of fecal-oral contamination of a food or water source and does not rule-out the possibility of another gastrointestinal pathogen.

More on: intestinal amoebae; Chilomastix mesnili

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.