Case #525 – October, 2020

A 45-year-old male who recently returned from a trip overseas to Korea presented to his primary care clinic for an annual checkup at a clinic in the United States. He had no major health problems, apart from reported mild, intermittent epigastric pain, nausea, and diarrhea. When questioned about his travel, he reported spending time in rural areas and consuming dishes likely containing undercooked frog meat. Because of this history, the physician ordered a stool ova and parasite (O&P) examination. Parasite eggs were detected on the formalin-ethyl acetate (FEA) concentrated wet mount, but the laboratory staff could not definitively identify them, so the specimen was forwarded to a reference laboratory. Figures A – D are the eggs, which measured an average of 58 x 39 µm. What is your diagnosis? Based on what features?

Figure A

Figure B

Figure C

Figure D

These images show Spirometra tapeworm eggs. In nearly all cases, infection with Spirometra in humans results in aimless migration of the plerocercoid larva (sparganosis). Rarely, maturation to adulthood occurs in the human intestine and eggs are shed in the feces (spirometrosis); such cases have been reported from China, Korea, Japan, and Vietnam. These eggs can be difficult to distinguish from those of the typical human-infecting Diphyllobothriids (Dibothriocephalus, Adenocephalus, Diphyllobothrium), but are often asymmetrical, tapered to conical on the opercular end, and the abopercular knob is minute to absent. The edges of the large operculum are indented (black arrows) and some species may show irregular pitting of the surface (white arrows), which is another feature that may help distinguish from typical Diphylobothriids. They are also smaller than Echinostomatid fluke eggs, which are usually longer than 80 µm. Ideally, this identification should be confirmed morphologically and/or molecularly using expelled proglottids or strobilae.

For more information on intestinal infections with Spirometra, see example case reports such as Le et al. 2017 and Lee et al. 1984

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.

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/.