Pediculosis differs from scabies infestation in that the louse resides on the hair or clothing and intermittently feeds on the host by piercing the skin. The bite causes small urticarial papules and itching. Head lice live close to the skin and may live for 30 days, depositing 100 to 400 eggs as nits on hair shafts, usually within 6 mm of the scalp.
Head lice are seen most frequently in early school-agechildren. Head lice infestations are unrelated to hygiene andare not more common among children with long hair orwith dirty hair. It is estimated that 6 to 12 million personsin the United States and 1% to 3% of persons in developedcountries are infested with head lice each year. In the UnitedStates, head lice infestation is rare among African Americansand may be more common in girls, which is attributed totheir tendency to play more closely with one another thanboys do.
Pubic lice are transmitted by sexual contact. Their presence in children may be a sign of child abuse. Body lice are firm evidence of poor hygiene, such as infrequent washing and clothing changes.
Itching, if present, is the primary symptom. Pediculosis capitis usually causes pruritus behind the ears or on the nape of the neck, or a crawling sensation in the scalp. Pediculosis pubis usually causes pruritus in the groin. Eyelash involvement in children may cause crusting and blepharitis. Pediculosis corporis causes pruritus that, because of repeated scratching, may result in lichenification or secondary bacterial infection. Excoriations and crusting, with or without associated regional lymphadenopathy, may be present.
Infestation with the head louse may be asymptomatic and has little morbidity. The diagnosis can be confirmed by visualizing a live louse. A fine-toothed comb to trap lice is more effective than simply looking at the hair. Wet combing is more time-consuming, but dry combing produces static that may propel the lice away from the comb.
Nits represent the outer casing of the louse ova. Viable nits have an intact operculum (cap) on the nonattached end and a developing louse within the egg. Brown nits located on the proximal hair shaft suggest active infestation. White nits located on the hair shaft 4 cm or farther from the scalp indicate previous infestation. Because nonviable nits can remain stuck in the hair for weeks to months after an infestation has resolved, many children with nits do not have active lice infestation.
The treatment of head lice is controversial because of resistance to many established options. Over-the-counter permethrin (1%) and pyrethrin-based products (0.17% to 0.33%)are the first choices of therapy. Because 20% to 30% of eggsmay survive one treatment, a second treatment should beapplied in 7 to 10 days. Drug resistance is on the rise, andmalathion (0.5%) lotion may be used as an alternative forresistant cases.
Everyone in the family should be checked for head lice and treated if live lice are found to reduce the risk of reinfestation. Bed linens, towels, and clothes worn for the previous 2 days before treatment should be machine-washed in hot water and machine-dried using high heat. Items that are not washable may be dry-cleaned or placed in a sealed plastic bag for 2 weeks. Brushes and combs should be soaked in dish detergent or rubbing alcohol for 1 hour. Rugs, furniture, mattresses, and car seats should be vacuumed thoroughly.
Manual removal of nits after treatment is not necessary to prevent spread. Children treated for head lice should return to school immediately after completion of the first effective treatment or first wet combing, regardless of the presence of remaining nits. There is no evidence that no nit or nit-free policies reduce transmission of head lice. If required for return to school, nit removal is best achieved by wetting the hair and combing with a fine-toothed metal comb.