Case #466 - April, 2018

A 6-year-old girl, who originally lived in Japan but now resides in the United States, was seen by a health care provider for abdominal pain and diarrhea. A stool specimen was collected and the object shown in Figure A was observed in the specimen. It was sent to the CDC DPDx Team for identification. The object was cleared using lacto-phenol and Figure B shows what was observed using a dissecting microscope. What is your diagnosis? Based on what criteria? Would you suggest any other test(s)?

Parasitic image

Figure A

Parasitic image

Figure B

This was a case of diphyllobothriasis caused by infection with a tapeworm in the family Diphyllobothriidae based on the presence of proglottids. Morphologic features shown included:

  • craspedote (overlapping) proglottids that are wider than long.
  • a single genital pore located midventrally.
  • rosette-shaped uteri.

Note that the taxonomy of the Diphyllobothriidae has recently been revised based upon mitochondrial DNA analysis (reference: Waeschenbach, A. 2017. Int J Parasitol 47: 831-843). A species identification is not necessary for proper management but can be useful for epidemiological studies.

Dibothiocephalus latus (formerly Diphyllobothrium latum), Adenocephalus pacificus (formerly Diphyllobothrium pacificum) and Dibothriocephalus nihonkaiense (formerly Diphyllobothrium nihonkaense) are the more common species reported in humans. Several other species of the family Diphyllobothriidae have been reported to infect humans, but less frequently; these include Dibothriocephalus ursi, Dibothriocephalus dendriticum, Diphyllobothrium cordatum, Diphyllobothrium lanceolatum, Diphyllobothrium dalliae, and Diphyllobothrium yonagoensis. A species identification may be possible by morphologic examination of the scolex of some species, if it is recovered, however molecular methods are the most accurate and are the preferred method.

More on diphyllobothriasis:

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Page last reviewed: May 30, 2018