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Case #498 - August, 2019

A 32-year-old man presented with loose stools for a couple of weeks and a history of abdominal pain and a pseudo-jejunal obstruction from a nodule. The nodule was excised, sectioned and stained with Hematoxylin and Eosin (H&E). Images taken at 200x and 400x shows what appears to be a cross section of a worm (Figures A and B). What is your diagnosis? Based on what morphological features?

Figure A

Figure A

Figure B

Figure B

This was a case of anisakiasis caused by Anisakid worm most likely in the genus Anisakis or Pseudoterranova. A third genus Contracaeceum is more rarely the cause of human infections. Diagnostic morphologic features included:

  • prominent lateral chords (blue arrow, Figure B);
  • multi-layered cuticle (red arrow, Figure B);
  • tall, prominent characteristic muscle cells (MU); and
  • portion of the excretory cell (green arrow, Figure B).
Figure B

Figure B

It is not required to identify Anisakid worms to the genus level for patient management. However, distinction may be accomplished by examination of esophageal and intestinal morphology after clearing in lactophenol and by the shape of the lateral chords in histologic sections.

For more information on anisakiasis, please click here: https://www.cdc.gov/dpdx/anisakiasis/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: October 31, 2019