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Lice can infect
the scalp, body, pubis, and eyelashes. Head lice are transmitted
by close contact; body lice, in cramped, crowded conditions; and
pubic lice, by sexual contact. Symptoms, signs, diagnosis, and treatment
differ by location of infestation.
Lice are wingless, blood-sucking insects that infest the head (Pediculus
humanus var. capitis), body (P. humanus var. corporis), or pubis (Phthirus pubis). The 3 kinds of lice differ substantially in morphology and clinical features. Head lice and pubic lice live directly on the host; body lice, in garments. All types occur worldwide.
Head
lice:
Head lice are most common in girls aged 5 to 11 but can affect almost anyone; infestations are rare in blacks. Head lice are easily transmitted from person to person with close contact (as occurs within households and classrooms) and may be ejected from hair by static electricity or wind; transmission by these routes (or by sharing of combs, brushes, and hats) is likely but unproven. There is no association between head lice and poor hygiene or low socioeconomic status.
Infestation typically involves the hair and scalp, but the eyebrows, eyelashes, and beard may be involved as well. Active infection usually involves ≤ 20 lice and causes severe pruritus. Examination is most often normal but may reveal scalp excoriations and posterior cervical adenopathy.
Diagnosis depends on demonstration of living lice. These are detected by a thorough combing-through of wet hair from the scalp with a fine-tooth detection comb; lice are usually found at the back of the head or behind the ears. Nits are ovoid, grayish white eggs fixed to the base of hair shafts. Each adult female louse lays 3 to 5 eggs/day, so nits typically vastly outnumber lice and are not a measure of severity of infection.
Treatment is outlined in Table 1: Parasitic Skin Infections: Treatment Options for Scabies and Lice . Drug resistance is common and should be managed with use of oral ivermectin and by attempting to rotate pediculicides. Termination of live (viable) nits is important in preventing reinfestation; live nits fluoresce on illumination with a Wood's lamp. Most pediculicides also kill nits. Dead nits remain after successful treatment and do not signify active infection; they do not have to be removed. Nits grow away from the scalp with time; the absence of nits < 1/4 inch from the scalp rules out current active infection. Hot air has been shown to kill > 88% of eggs but has been variably effective in killing hatched lice. Thirty minutes of hot hair, slightly cooler than a blow drier, may be an effective adjunctive measure to treat head lice.
Controversy surrounds the need to clean the personal items of people with lice or nits and the need to exclude children with head lice or nits from school; there are no conclusive data supporting either approach.
Body lice:
Body lice primarily live on bedding and clothing, not people, and are most frequently found in cramped, crowded conditions (eg, military barracks) and in people of low socioeconomic status. Transmission is by sharing of contaminated clothing and bedding. Body lice are important vectors of epidemic typhus, trench fever, and relapsing fever.
Body lice cause pruritus; signs are small red puncta caused by bites, usually associated with linear scratch marks, urticaria, or superficial bacterial infection. These findings are especially common on the shoulders, buttocks, and abdomen. Nits may be present on body hairs.
Diagnosis is by demonstration of lice and nits in clothing, especially at the seams.
Primary treatment is thorough cleaning or replacement of clothing and bedding, which is often difficult because affected people often have few resources and little control over their environment.
Pubic lice:
Pubic lice (“crabs”) are sexually transmitted in adolescents and adults and may be transmitted to children by close parental contact. They may also be transmitted by fomites (towels, bedding, clothing). They most commonly infect pubic and perianal hairs but may spread to thighs, trunk, and facial hair (beard, mustache, and, in children, eyelashes).
Pubic lice cause pruritus. Physical signs are few, but some patients have excoriations and regional lymphadenopathy and/or lymphadenitis. Pale, bluish gray skin macules (maculae caeruleae) on the trunk, buttocks, and thighs are caused by anticoagulant activity of louse saliva while feeding; they are unusual but characteristic of infection. Eyelash infection manifests as eye itching, burning, and irritation.
Diagnosis is by demonstration of nits and/or living lice by close inspection (Wood's light) or microscopic analysis. A supporting sign of infection is scattering of dark brown specks (louse excreta) on skin or undergarments.
Treatment is outlined in Table 1: Parasitic Skin Infections: Treatment Options for Scabies and Lice. Treatment of eyelid and eyelash infection is often difficult and involves use of petrolatum, physostigmine ointment, oral ivermectin , or physical removal of lice with forceps. Sex partners should also be treated.
Last full review/revision September 2008 by James G.H. Dinulos, MD
Content last modified September 2008
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