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Case #141 - October, 2004

An 10-year-old boy was taken to his pediatrician due to intestinal symptoms, including diarrhea, after he returned home from summer camp. The physician requested several exams, including an ova and parasite (O & P) examination; the stool specimen was tested at a commercial laboratory where a concentration method was performed and wet-mount slide examined. One of the exams ordered by the physician was positive for a bacterial agent. However the objects seen in Figures A and B (magnification 400×) were observed in the stool samples in low numbers. Please provide a complete identification of the objects in the images.
Figure A

Figure A

Figure B

Figure B

Answer to Case #141

This was a case of hymenolepiasis caused by Hymenolepsis nana (the dwarf tapeworm). Morphologic features seen in the images of the eggs were:

  • eggs with a thin, hyaline shell and an oncosphere in which hooks can be seen. Six hooks should be present, but they are not always visible in the same focal plane.
  • the size of the eggs, which was consistent with those of H. nana (30 to 47 micrometers in diameter). Size is one of the primary features used to distinguish eggs of H. nana from those of H. diminuta.
  • the presence of polar filaments (indicated by arrows in Figures A and B below), which H. diminuta lacks.

Figure A

Figure B

More on: Hymenolepiasis

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: August 24, 2016