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Case #408 - November 2015

A 65-year-old man from rural Canada presented with pruritus on his chest; he mentioned that even with frequent bathing the symptoms persisted. Possible arthropod ectoparasites were observed on his chest hair (Figure A) and a specimen was collected and sent to the Microbiology lab for examination. Figure B shows a close-up of one of the organisms observed by the attending microbiologist. The object measured 1.5 mm in length. What is your diagnosis? Based on what criteria?

Case408_A

Figure A

Case408_B

Figure B

Case Answer

This was a case of phthiriasis caused by the human pubic louse, Pthirus pubis. Diagnostic features included:

  • lice with a body nearly as wide as long (Figure B), consisting of six legs, one pair of eyes, and one pair of antennae.
  • raptorial (adapted for grasping) tarsal claws on the meso- (middle) and metathoracic (hind) legs that are larger than those on the forelegs (Figure B).
  • protuberances along the lateral margins of the abdominal segments (Figure B).
  • a nit (egg; arrow, Figure B) with a conical operculum.

While the chest is not a typical location for this species, P. pubis can be found on nearly any coarse hair on the body, including eye brows and eye lashes, and male facial hair.

More on: pthiriasis

This case and images were kindly provided by the Cadham Provincial Public Health Laboratory, Winnipeg, Manitoba, Canada.

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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
  • Page last updated: August 24, 2016
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