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Case #483 - January, 2019

As part of a health screening for refugees, a local private diagnostic laboratory was contracted to process fecal specimens. Smears were prepared from specimens collected and preserved in PVA (polyvinyl alcohol) and stained with iron hematoxylin. Stained smears were examined at 1000x oil immersion magnification and the objects of interest shown in Figures AC show what was observed on one smear. The objects measured 7-9 micrometers on average. What is your diagnosis?  Based on what criteria?

parasitic image

Figure A

parasitic image

Figure B

parasitic image

Figure C

The objects shown in this case were cysts of Chilomastix mesnili, a nonpathogenic flagellate.  Diagnostic morphological features shown included:

  • Lemon/lime ovoid-shaped cysts within the size range for C. mesnili (6-10 micrometers)
  • Cysts with a single large nucleus
  • Cysts with a cytostome and/or fibrils present

Although C. mesnili is considered a commensal organism, the presence can be an indicator of fecal contamination of food and/or water sources.

More on Chilomastix mesnili: https://www.cdc.gov/dpdx/chilomastix/index.html

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.

DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.

Page last reviewed: March 6, 2019