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Head lice treatment: dispelling the myths

Nigel Hill
PhD
Medical Entomologist
Disease Control and Vector Biology Unit
Department of Infectious and Tropical Diseases
London School of Hygiene and Tropical Medicine
E:nigel.hill@lshtm.ac.uk
W:www.lshtm.ac.uk

Head lice, Pediculus capitis, are wingless, dorso-ventrally flattened, obligate ectoparasites. Closely related are two other human blood-sucking lice, the body (or clothing) louse, Pediculus humanus, and the pubic or "crab" louse, Pthirus pubis. While head lice remain common among primary school-aged children in the UK, the incidence of body lice is now comparatively rare in developed countries, although quite common in vagrants or refugee situations where changes of clothing are limited. The prevalence of pubic lice is difficult to determine as most cases are detected only in referrals to STD clinics. Contrary to popular belief, pubic lice are not uncommon in facial hair, and a number of cases of eyelash infestation of young children are referred to the public health laboratory service entomological identification unit every year.

Despite huge advances in most forms of public health and communicable disease treatment in recent decades, control of head lice remains problematic, hampered by the misunderstanding and social stigma that still surround the subject, and made worse by pediculicides of increasingly poor efficacy. Each of these aspects must be addressed if we are to see real progress towards eradicating head lice in the future.

Dispelling the myths
It is widely believed that lice fly or jump from person to person, or that sharing hats, combs or pillows is a means of transmission, yet there is no evidence that anything other than prolonged head-to-head contact is required for lice to spread. Similarly, it is thought that those with lice will have an itchy scalp, but this is likely only after prolonged or heavy infestation. Although many think that a quick visual inspection of the head will locate lice in dry hair, in most cases where numbers are low it requires use of a fine-tooth comb in wet and preferably conditioned hair.

A good proportion of parents of children at primary school continue to call for the reinstatement of "nit nurse" inspections in classes, not realising that this activity had little impact other than being a huge drain on primary healthcare resources. The problem of social stigma may be harder to address - despite the fact that we know lice can, and do, infect anyone, regardless of socioeconomic class, there are still connections made between infection, poverty and personal hygiene.(1)

Treatment
At the present time, giving advice on the most appropriate means of treating head lice is far from straightforward. The mainstay of control, the licensed proprietary treatments based on insecticides, have been in widespread use for many years, and as a consequence the lice population is developing resistance, so no treatment is fully effective.(2,3) The products of choice based on the pyrethroids, permethrin and phenothrin, seem to be particularly ineffective.(2) Products based on the organophosphate malathion seem to have retained efficacy rather better, although this seems to depend on location.(2,3) Having been restricted to prescription-only status since 1996, carbaryl-based treatments are likely to be the most effective currently available, but cross-resistance to organophosphates may become a problem in the future, due to the similar mode of action of the two active compounds.(3)
 
The best advice is that, whichever pediculicide is used, it is vital to check success by wet fine-tooth combing a week after use to confirm eradication, and where treatment has failed, an unrelated treatment substituted. One point to remember, despite claims and instructions by the manufacturers, ovicidal activity is generally poor with these products, so double-dosing as recommended in the BNF or local authority guidelines should be followed.

In those cases where parents are reluctant to use insecticidal products, or where resistance has been confirmed, there is growing evidence that a structured course of wet combing with conditioner, known as "Bugbusting" by the charity Community Hygiene Concern, can be successful. While more time-consuming than traditional pediculicides, this method does not suffer the problem of resistance and may be cost-effective in the long term. Unfortunately, perhaps as a consequence of the reduced efficacy of traditional products, the number of unlicensed "cures" for lice on the market has escalated. Substances such as tea tree oil and other herbal remedies make claims of safety and efficacy, despite never having been fully evaluated. Such unlicensed products are being marketed illegally in the UK, and health professionals should discourage their use.

A new generation of pediculicides containing new actives is currently undergoing clinical evaluation, so the outlook is not all doom and gloom. However, it will be a while before we return to the days of quick and easy control.

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References

  1. Figueroa JI. Head lice: is there a solution? Curr Opin Infect Dis 2000;13:135-9.
  2. Downs AMR, Stafford KA, Harvey I, Coles GG. Evidence for double resistance to permethrin and malathion in head lice. Br J Dermatol 1999;141:508-11.
  3. Downs AMR, Stafford KA, Hunt LP, Ravenscroft JC, Coles GG. Widespread insecticide resistance in head lice to the over-the-counter pediculicides in England, and the emergence of carbaryl resistance. Br J Dermatol 2002;146:88-93.

Resources
Public Health Advisory Service
T:09001 600278 (calls cost 50p per minute)
Community Hygiene Concern
W:www.chc.org