The facts of lice
CMAJ 1997;157:747
© 1997 Canadian Medical Association
With the start of school and daycare this fall, physicians will once again confront the head louse, Pediculus capitis. How can it be recognized, and what is the best treatment? The Canadian Paediatric Society recently issued a statement regarding diagnosis and treatment.1
The head louse infests the scalp, and only the scalp. It is not the same as Pediculus humanus (the body louse), which is responsible for the spread of diseases such as typhus, or Phthirus pubis (the crab louse), which is spread by sexual contact. Physicians should inform patients of the distinctions among these lice and reassure patients that head lice do not spread disease.
The louse is a blood-sucking ectoparasite transmitted by direct contact. The parasites commonly infest young children and families. Children are often diagnosed at school or in daycare centres and referred to a family physician. Up to 10% of elementary school children may have infestations. Social class and level of personal cleanliness are not predictors of infestation. Keeping hair short, brushing it or shampooing it have no effect on the likelihood of infestation.
Symptoms are usually mild and may be absent. Itching is the main complaint, occasionally accompanied by excoriation and crusting. Rarely, a secondary bacterial infection and regional adenopathy may develop. Diagnosis is made by careful inspection of the scalp. The adult louse is 2 to 4 mm and grey and may be found near the hairline at the nape of the neck and behind the ears. The eggs are contained in whitish shells (nits) on the hair shaft 3 to 4 mm from the scalp surface. They are firmly attached and cannot be easily removed, distinguishing them from normal hair scale.
Once infestation with Pediculus capitis is diagnosed, treatment is required. There are a number of agents available. Permethrin (Nix), a cream rinse, destroys both lice and eggs. About 1% of patients experience a mild dermal reaction after using it. Lindane (Kwellada) is commonly used by the public; however, it is less effective than permethrin, and there have been reports of neurotoxicity resulting from its misuse. Pyrethrin products (R&C Shampoo and Lice-Enz) are safer than lindane, but not as ovicidal. Acetomicellar complex (SH-206TM, Pharmascience) is touted as a natural product. Although there is some preliminary evidence that it may work, there are no published studies of its efficacy.
All antilice products should be used according to instructions on the product package. A second application is recommended 10 days after the first to kill any lice hatched from eggs that were not killed in the first application. If live lice are detected by inspection 24 to 48 hours after the initial treatment, resistance to the product should be suspected. In such cases, immediate treatment with a different pediculicide is recommended. This should be followed by a second treatment 7 days later.
Family members, school friends and children in the same daycare as patients should be examined and treated if infested. Children can return to their usual activities and school or daycare after the first treatment.
Families may wish to wash hats and other headgear, pillow cases and towels in hot water. Combs and brushes can be soaked in hot water for 10 minutes or washed with a pediculicide. Pediculicides are harmful if used improperly and must be safely stored out of the reach of child.
A patient-information sheet called "Myths and facts about head lice" is available from the CPS, 401 Smyth Rd., Ottawa ON K1H 8L1; tel 613 737-2728, fax 613 737-2794; www.cps.ca. It may be reproduced without permission. -- JH
Reviewed by Dr. Noni MacDonald, Children's Hospital of Eastern Ontario, Ottawa, Ont.
Reference
- Head lice infestations: a persistent itchy 'pest.' Paediatr Child Health 1996;1(3):237-49.
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