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Case #419 - May 2016

A 23-year-old female presented to her primary care provider with abdominal pain, cramps, flatulence, and diarrhea five days after returning from a white water rafting trip in the Grand Canyon, Arizona. Stool specimens were collected in 10% formalin and zinc polyvinyl alcohol (Zn-PVA) and sent to a reference lab for routine ova-and-parasite (O&P) testing. Figures A-D show what was observed on a trichrome-stain slide of stool preserved in the Zn-PVA. Images were captured at 1000x magnification with oil. What is your diagnosis? Based on what criteria?

Figure A

Figure A

Figure B

Figure B

Figure C

Figure C

Figure D

Figure D

This case demonstrated a mixed infection of Giardia duodenalis and Blastocystis hominis. Diagnostic morphologic features included:

  • ellipsoidal cysts of within the size-range (8-19 μm) for G. duodenalis (Figures A, C, D) that contained multiple nuclei, fibrils, and axonemes.
  • pyriform trophozoite within the size range (10-20 μm) for G. duodenalis (Figure B) that contained fibrils,median bodies, two nuclei, and sucking disks.
  • cyst-like forms of B. hominis (Figures A-D) containing a large central body surrounded by a narrow rim of cytoplasm containing nuclei and inclusion bodies.

More on: Giardiasis, Blastocystis hominis infection

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

Page last reviewed: August 24, 2016