Case #475 - September, 2018

An ova-and-parasite screening was performed on a group of school-age children, which included both formalin and zinc polyvinyl alcohol (Zn-PVA) preserved stool specimens. Concentration by sedimentation was performed on the formalin preserved specimens and no helminth ova or protozoa cysts were found in any specimen. Smears were made from the PVA preserved specimens, stained with trichrome and examined. Figures AD show what was found in one specimen. The objects of interest measured 6 micrometers long on average. What is your diagnosis? Based on what criteria?

parasitic image

Figure A

parasitic image

Figure B

parasitic image

Figure C

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Figure D

parasitic image

Figure E

The organism detected was Enteromonas hominis, a nonpathogenic flagellate. Morphologic features shown in the images included:

  • Small cysts within the size range for E. hominis (4-8 micrometers) with 1-4 nuclei (Figures A, B and E) that resembles cysts of E. nana, only smaller.
  • Trophozoites (Figures C, D and E) that were oval with a single nucleus within the size range for E. hominis (4-10 micromenters).

The presence of E. hominis can be an indicator of fecal contamination of a food or water source and does not rule other parasitic infections.

More on E. hominis:

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

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Page last reviewed: November 15, 2018