(Pubic Lice, Crab Lice)

Pruritus of the anogenital area is a common symptom in pubic lice infestations ("crabs" or "pthiriasis"). The parasite most frequently is found in the pubic region but also can infest on the eyelashes, eyebrows, beard, axilla, perianal area, and rarely, the scalp. A characteristic sign of heavy pubic lice infestation is the presence of bluish or slate-colored macules (maculae ceruleae) on the chest, abdomen, or thighs.

Etiology

Pthirus pubis is the pubic or crab louse. Nymphs and adult lice feed on human blood.

Epidemiology

Pubic lice infestations are more prevalent in adults and usually are transmitted through sexual contact. Transmission by contaminated items, such as towels, would be uncommon. Pubic lice on the eyelashes of children may be evidence of sexual abuse, although other modes of transmission are possible. Infested people should be examined for other sexually transmitted infections, including syphilis and infection with Neisseria gonorrhoeae, Chlamydia trachomatis , hepatitis B virus, and human immunodeficiency virus. Adult pubic lice can survive off a host for up to 36 hours, and their eggs can remain viable for up to 10 days under suitable environmental conditions.

The incubation period from the laying of eggs to the hatching of the first nymph is approximately 6 to 10 days. Adult lice capable of reproducing do not appear until approximately 2 to 3 weeks after hatching.

Diagnostic Tests

Identification of eggs (nits), nymphs, and lice with the naked eye is possible; the diagnosis can be confirmed by using a hand lens or microscope.

Treatment

All hairy areas of the body should be examined for evidence of pubic lice. Lice and their eggs can be removed manually, or the hairs can be shaved to eliminate immediately the infestation. Caution should be used when inspecting, removing or treating lice on or near the eyelashes. The pediculicides used to treat other kinds of louse infestations are effective for Treatment of pubic lice (see Pediculosis Capitis). ReTreatment is recommended as for head lice. Topical pediculicides should not be used for infestation of eyelashes by pubic lice; petrolatum ointment applied to the eyelashes 2 to 4 times daily for 8 to 10 days is effective.

Isolation of the Hospitalized Patient

In addition to standard precautions, contact precautions are recommended until the patient has been treated with an appropriate pediculicide.

Control Measures

All sexual contacts should be examined and treated, as needed. Patients should be advised to avoid sexual contact until they and their sex partner have been treated successfully. Bedding, towels, and clothing can be decontaminated by laundering in hot water and machine drying using a hot cycle or by dry cleaning.