Pediculosis

Published on 18/03/2015 by admin

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Last modified 18/03/2015

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Pediculosis

Jaime R. Gropper and Jacob O. Levitt

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Lice are wingless, dorsoventrally flattened, blood-sucking insects that are obligate ectoparasites of birds and mammals. Pediculosis denotes an infestation by Pediculus capitis (head louse), Pediculus humanus (body or clothing louse), or Phthirus pubis (pubic or crab louse). The bites of lice are painless and can rarely be detected. The clinical signs and symptoms are the result of the host’s reaction to the saliva and anticoagulant injected into the dermis by the louse at the time of feeding. Depending on the degree of sensitivity and previous exposure, the feeding sites may produce red macules or papules hours to days after feeding. Pruritus is the most common symptom of any type of pediculosis. If left untreated, superinfection of excoriations may lead to impetiginous crusts and regional lymphadenopathy.

Pediculosis capitis

Management strategy

Infestation is most common among children 3–12 years of age and their parents. Identification of live lice is the gold standard of diagnosis; however, finding nits alone in a patient who has not been treated also warrants treatment. One study showed that about 20% of patients found to have nits alone go on to develop lice. Nits are easier to spot, especially at the nape of the neck and behind the ears. Hatched nits are white, unhatched nits are brown. Detection combing of wet hair with a fine-toothed nit comb allows for efficient recovery of lice and nits for diagnosis.

Management must take into consideration key elements of the head louse lifecycle. A nervous system develops in the egg by day 4, it takes 12 days at most to hatch, and the nymph can lay eggs as soon as 7 days after hatching. Contrary to the directions of most non-ovicidal pediculicides, one re-treatment at 7 days will not kill all viable nits. As such, therapies that do not kill eggs require 3 weekly treatments. Pediculicides that are also ovicidal require two treatments separated by 1 week. Ova less than 4 days old will not be affected by agents that act on the louse nervous system. Lice are sensitive to dehydration but can live off the host for up to 55 hours. Transmission is mainly by direct head to head contact. Indirect spread through fomites is also possible. Until definitive safety data are available, the occasional patient under the age of 2 years probably should be treated with mechanical methods.

Launderable items (worn clothing and used bedding, towels, scarves, and hats) should be placed in a dryer at 60°C (i.e., on high) for 10 minutes. Brushes, combs, and hair ornaments can be placed in hot (60°C or more) water for 10 minutes. Non-launderable items (i.e., certain stuffed animals) should be placed in a bag for 3 days (not 15 days, as eggs laid off a host are unlikely to hatch close enough to a host to obtain their first blood meal). Cloth furniture and rugs should be vacuumed. Fumigation of the home is discouraged.

Contacts of index cases, including classmates, should be screened. Empiric therapy for close household contacts, particularly if they share a bed, is justifiable. Those likely to have had head-to-head contact with the index case in the prior 4 to 6 weeks should be identified and screened. Children should not be excluded from school for head lice as the infestation often has been ongoing for months prior to its detection. Hair grows 1 cm per month, and lice lay eggs close to the scalp where it is moist and warm. Nits detected 2 cm from the scalp represent a 2-month-old infestation. Requiring therapy within a week of the detected infestation is more reasonable.

Considerations guiding therapy include safety and efficacy, which for chemical modalities depend largely on regional resistance patterns of the lice. Because of widespread resistance to permethrin and lindane, malathion formulated in isopropyl alcohol with terpineol, being both ovicidal and pediculicidal, was the most effective therapy at the time of the last writing and remains as such. Important new topical treatment options in light of growing resistance to treatment are benzyl alcohol lotion, spinosad topical suspension, and ivermectin lotion. Carbaryl is a good alternative but occasional resistance has been reported. Alternatives to agents that do not act on the louse nervous system include mechanical methods of louse occlusion, cuticle disruption, or physical removal. Barring shaving the head, these modalities are often unreliable and have the attendant problem of recurrent infestation occurring between treatments and continued infectiveness.

First-line therapies

imageBenzyl alcohol 5% lotion A
imageCarbaryl 0.5% lotion E
imageIvermectin 0.5% lotion A
imageMalathion 0.5% lotion A
imagePermethrin 1% creme rinse A
imageSpinosad 0.9% topical suspension A

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