Pediculosis can be very pruritic. There are three forms in humans: pediculosis pubis caused by Phthirus pubis, pediculosis capitis caused by Pediculus capitis, and pediculosis corporis caused by Pediculus corporis.

Pediculosis capitis is found only in preadolescent children and almost never in African-American children, for unknown reasons. Scratching can cause a secondary bacterial infection. Crusting appears on the scalp, and excoriations appear on the neck and ears. Occipital and cervical lymph nodes are palpable. Live nits are whitish and shiny and found within 1 cm of the scalp (Fig. 5-1). Dead nits are dull and gray.

Pediculosis pubis is caused by a crab-like organism; hence, the term “crab lice” infestation. The louse grasps the hair and bites the skin, often producing bluish macules 0.5 to 2.5 cm in diameter (maculae cerulea). The nit is 3 to 4 mm in length. Although generally found on the pubic hairs, the crab louse attaches to hair on other parts of the body, such as the scalp or axilla. Pediculosis ciliaris, seen mostly in children, is due to pubic louse infestation of the eyelids.

Pediculosis corporis is caused by a larger louse that feeds on the skin but does not remain attached to it, preferring to reside in the seams of clothing. Intense itching leads to eczematization—vagabonds’ disease. Body lice can transmit epidemic typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and louse-borne relapsing fever (Borrelia recurrentis).