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Head lice: offering resistance, but the battle can be won

Nigel Hill
BSc
Medical Entomologist and Head Technologist
Disease Control and Vector Biology Unit
Department of Infectious and Tropical Diseases
London School of Hygiene and Tropical Medicine
E:n.hill@lshtm.ac.uk

Infestation with head lice (pediculosis) is a widespread, persistent and recurring problem. Despite tremendous advances in medicine in recent years, we still find ourselves in the situation where it is unlikely there are fewer cases of head lice in our children now than there were three decades ago. In our defence, it is the behaviour of the head louse, Pediculus capitis, that makes it fundamentally difficult to control. Not only does it move rapidly and have the ability to camouflage itself to some degree, by taking on a similar colour to the hair it hatches on, but also most cases consist of very few lice, often less than 10 individuals, so only a fraction of active cases are ever detected or treated at any given time. What are the options for treatment?

Medicated treatments
Quite rightly, medicated treatments are the mainstay of control in our "quick fix" society. Early reports of control failure were dismissed by many as failure to follow manufacturers' instructions. However, field studies have demonstrated clear problems with resistance, which poses a serious threat to current control policy. The most recent clinical evaluations in the UK report an alarming trend, with a failure rate for malathion(1,2) ranging from 22-64% and a staggering 87% for permethrin.(2) The remaining active treatment - carbaryl - is available only on prescription. Fortunately, there are a number of alternative classes of insecticide currently being investigated. Among these, insect growth regulators (IGRs) and the neonicotinoids, such as imidacloprid, are the most promising.

Unlicensed chemicals
Failure of existing products is one of the main reasons an increasing number of people are turning to unlicensed products. However, there is growing concern at the number of essential oils and other substances being proffered as alternative cures for head lice. Not only are such chemicals of dubious efficacy, but their safety record is unknown. Many of these are presented as "safe" alternatives to conventional pediculocides, although many are more toxic, volume per volume, than insecticides in current use. It is ironic that widely advocated tea tree oil, for example, has a higher mammalian toxicity(3) than either permethrin or malathion. Many other essential oils in these unlicensed products are listed as potentially harmful to children.(3) Despite its apparent reluctance to intervene in this area, the MCA is charged with regulating any product making claims to kill or repel head lice, and the bottom line for all health professionals should be to dissuade the public from resorting to such alternative treatments.

Physical methods
Wet combing with conditioner (WCWC) - sometimes called "bug busting" - is frequently put forward as an effective means of control but this has yet to be proven. Clearly, as a means of detecting lice, few will disagree that it is an excellent method. The combination of water and normal conditioner act to keep lice still and ease the progress of a fine-tooth comb through the hair with maximum speed and minimum discomfort, even in long or curly hair.
To date there has really only been one convincing clinical evaluation of WCWC as a means of control, which reported moderate efficacy of around 40%. Despite this, it is not unreasonable to suggest WCWC could play a role in control due to the lack of currently available and effective pediculocides. Its biggest drawback is the amount of time and dedication needed to ensure all lice are removed from the head on each of five successive sessions over two weeks.
Whatever happens in the coming years, the health centre, and the practice nurse in particular, will remain a focus for those seeking advice and treatment for head lice. The biggest impact could be made by putting the problem into context for distraught parents. Head lice are of no real medical importance. Anyone can get head lice - they are not choosy about social status, creed or colour.
Despite the problems of resistance, the first-line treatment in most cases will remain licensed medicated products. Where the family is receptive or when available chemical treatments are shown to be ineffective, it may be beneficial to explain the concept of WCWC. In all cases, ensure a policy of frequent detection by all close contacts to eliminate sources of reinfection and, most importantly, to establish whether the treatment has been successful.(4)
Without doubt, the most helpful thing we can do is to discuss the matter in an open and understanding manner, to dispel those myths and allay any fears. Let's all help to overcome the stigma that continues to surround this subject.

References

  1. Roberts RJ, Casey D, Morgan DA, Petrovic M. Comparison of wet combing with malation for treatment of head lice in the UK: a pragmatic randomised controlled trial. Lancet 2000;356:540-4.
  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. Tisserand R, Balacs T. Essential oil safety - a guide for health care professionals. Edinburgh: Churchill Livingstone; 1995. p. 45-55.
  4. Figueroa JI. Head lice: is there a solution? Curr Opin Infect Dis 2000;13:135-9.

Resources
Public Health Advisory Service
T:09001 600 278
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Community Hygiene Concern
W:www.chc.org