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?

Figure A

Figure B

This was a case of pthiriasis 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.