Common skin infections in children: Scabies and head lice

In the third part of our series about common skin infections in children, Michael J Sladden and Graham A Johnston review scabies and head lice

Childhood skin infections are commonly seen in both primary care and dermatology practice worldwide. They consume considerable resources and need careful management. However, education and reassurance of patients and parents, combined with simple treatment and self management, play a vital role in successful treatment.

Scabies

Scabies is an intensely itchy dermatosis caused by the mite Sarcoptes scabiei. The infestation can occur at all ages but particularly occurs in children. It is a common public health problem in poor communities and developing countries.

Scabies is highly contagious and is spread from person to person by direct skin contact. Transfer from clothes and bedding occurs rarely and only if contaminated by infectious people immediately beforehand. Infestation occurs when pregnant female mites burrow into the skin and lay eggs. After two or three days the larvae emerge and dig new burrows. They mature, mate, and repeat this cycle every two weeks.

Typical childhood scabies, showing multiple puritic papules,
vesicles, and pusules. The pathogonomic scabetic burrows are anchored

The main symptoms of scabies are caused by the host immune reaction to burrowed mites and their products. Symptoms appear within two to six weeks of the initial infestation, but reinfestation can provoke symptoms within 48 hours. The most common presenting lesions are papules, vesicles, pustules, and nodules. The pathognomonic sign is the burrow - a short, wavy, grey line that is often missed if the skin is eczematised, excoriated, or impetiginised. In adults, scabies is characterised by intractable pruritus, which is worse at night, and lesions in the web spaces, fingers, flexor surfaces of the wrists, axillae, and genital areas.

In infants and young children, scabies often affects the face, head, neck, scalp, palms, and soles (fig 1). Widespread eczematised erythema is common, particularly on the trunk, and is sometimes more troublesome than are lesions at typical sites. Very young babies do not scratch and may just seem miserable or feed poorly. Pinkish brown scabetic nodules are common in babies and can resemble mastocytomas or other infiltrative conditions.

A high index of suspicion is needed to make the correct diagnosis of scabies because of the wide range of symptoms and presentations. For example, the distribution of lesions in adults (rarely on the face and neck) and children (commonly on the face and neck) is different. A history of itching in several family members over the same period is virtually pathognomonic of scabies. Lack of a history of itching in family members does not exclude scabies, however, because family members may not admit to a history of possible scabies, and some people with scabies genuinely do not itch. Untreated, scabies can continue for many months. Recurrence of symptoms after treatment does not exclude scabies.

The definitive diagnosis of scabies relies on microscopic identification of mites, eggs, or faecal pellets from burrow scrapings. Treatment should be given if scabies is suspected, even without microscopic evidence. A variety of effective topical medications are available to treat scabies, including permethrin, malathion, benzyl benzoate, lindane, and crotamiton. Treatment selection is determined by factors such as the age of the child (see www.bnf.org), local experience of and resistance patterns to scabeticides, drug toxicity, and (particularly in underdeveloped countries) cost and availability. Children should be given aqueous preparations, as alcoholic lotions sting and can make them wheeze. Topical preparations must be applied correctly to maximise the success of treatment (box).

Permethrin 5% dermal cream is the treatment of choice for scabies in the United Kingdom, Australia, and the United States. It is the most effective topical agent, is well tolerated, and has low toxicity (www.bnf.org). It should be applied on two occasions, one week apart. For children under 2 years, medical supervision is needed.

Malathion is the second choice for treatment. Medical supervision is needed for children under 6 months. Malathion is cheaper than permethrin and, for adult contacts, cheaper than a prescription.

Pediculosis capitis, showing live lice and nits

Lindane is less effective than permethrin and has been withdrawn in many countries because of reports of aplastic anaemia and concerns about potential neurotoxicity. Benzyl benzoate is irritant and not recommended for children.

The oral antiparasitic drug ivermectin is an effective scabicide. Two doses of ivermectin (200 µg/kg body weight, two weeks apart) seem to be as effective as a single application of permethrin. However, the drug has not been evaluated in children weighing less than 15 kg, and its role in treating scabies remains unclear.

Head lice (pediculosis capitis)

Pediculosis capitis is a scalp infestation by the human head louse (Pediculus humanus capitis) (fig 2). Head lice infestation is common throughout the world, crossing all economic and social boundaries. It is most common in children aged 4-11 years, but occurs in people of all ages. In Western societies, parents are often embarrassed if children have head lice, because of the misconception that lice are associated with poor hygiene. In other societies, the infestation is considered normal. The worldwide cost of treatment is high.

The head louse is a grey-brown, six legged wingless insect, 1-3 mm long, which feeds by sucking blood from the host's scalp. Once infestation occurs, the female louse mates and lays eggs within two days of becoming an adult. The eggs (nits) are deposited on a hair, attached close to the scalp by a glue-like glandular secretion. They hatch in seven days, and the eggshells are left empty. Young lice (nymphs) take 10-14 days to become adults, when they too begin laying eggs. The infestation spreads from person to person only by relatively prolonged head to head contact, usually occurring between people who know each other well. Head lice found on hats, pillows, and other locations are usually dead or sick and unlikely to transmit the infestation. Most people are initially asymptomatic and unaware of the infestation, because pruritus, an allergic reaction to louse saliva, takes up to three months to develop. Head lice infestation is a common cause of scalp impetigo in developed countries, but is not a vector for other diseases.

A diagnosis of active infestation is confirmed by the existence of live lice. The presence of eggs alone (without live lice) may reflect previous or treated infestation. Treatment should not be applied unless live lice are discovered, in order to minimise the development of drug resistance. Automatic treatment of family members is not necessary, but contacts should have detection combing for live lice and be treated if positive.

There is good evidence that permethrin,  synergised pyrethrin (natural pyrethrin combined with other agents to enhance activity), and malathion  are effective at treating pediculosis capitis. However, as resistance to insecticides is increasing, treatment should be based on local experience and resistance patterns.

Head lice infestation should be treated with lotion or liquid formulations. Shampoos are diluted too much in use to be effective. We advise the use of aqueous solutions (not alcohol based preparations) to avoid skin irritation and wheeze. At least 50 ml (100 ml for thick hair) should be applied to the whole scalp and left on for 12 hours. Although one treatment application is usually adequate, a second application seven days after the first is recommended because some eggs may survive. Under-treatment in the presence of newly hatched young lice exacerbates drug resistance. To reduce the development of resistance, if a course of treatment fails to provide a cure (live lice present after second application), a different insecticide should be used for the next course.

Malathion 0.5% (aqueous) liquid is rubbed into dry hair and scalp and allowed to dry naturally. It should be washed off after 12 hours and the application repeated after seven days (www.bnf.org). It is highly effective at killing both adult lice and ova. Medical supervision is needed for children under 6 months,.

Although permethrin is active against head lice, the formulations and licensed methods of application of products currently available in the UK make them unsuitable for treating head lice. Our local practice is to use permethrin 5% dermal cream massaged into the scalp overnight and washed off the next morning, repeated after one week (off licence). This seems effective and overcomes problems of insecticide dilution and short contact time.

Carbaryl 1% aqueous liquid, used similarly to malathion, is also effective at treating head lice. However, because there is a theoretical risk that it may be a human carcinogen, it is available only on prescription in the UK. For children under 6 months, medical supervision is needed.

Mechanical measures, such as "wet combing," have been used as adjuncts to insecticides, but evidence suggests they are unhelpful. "Bug busting" involves meticulous combing of wet hair with the detection comb (half an hour each time) over the whole scalp every four days for a minimum of two weeks, with the aim of eradicating lice. Little evidence exists to show that "bug busting" is effective, however, and it should not be advocated as first line treatment in the general population.  Electronic combs and tea tree oil have also been used to treat head lice, but evidence of effectiveness is lacking. In developing countries, where products are usually unavailable or prohibitively expensive, patients may choose cheaper or traditional treatments (for which there is little evidence) or low grade agricultural insecticides (which can be fatal).

Persistent head lice is a common and frustrating problem. It is important to explain to parents the difference between resistance and reinfection. Parents should liaise with the school if their children have head lice.

Michael J Sladden, consultant dermatologist
Email: m.sladden@doctors.org.uk

Graham A Johnston, clinical epidemiologist and specialist registrar in dermatology, Department of Dermatology, Leicester Royal Infirmary, University Hospitals of Leicester NHS Trust

We thank Julie Sladden for reading and reviewing the manuscript.

studentBMJ 2005;13:221-264 June ISSN 0966-6494

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