Combing out pesticides

Head lice are a common pest in childrens’ hair. Contrary to popular belief, lice on a chil­d’s scalp have nothing to do with cleanli­ness, and even the cleanest head can harbour these arthropods. Mark Davis of the Pesticides Trust [now PAN UK] investigates the root of the problem.

Head lice are transmitted by direct head to head contact when the adult louse moves through the hair and towards the scalp where they feed on blood. Mature lice mate and the females lay eggs which are attached to a single hair. Eggs hatch within 10-14 days and develop through three nymphal stages to adulthood.
    The most widely used method for con­trolling head lice cur­rently relies on the application of lotions containing insecti­cides such as carbaryl, mala­thion, perm­ethrin, phenothrin, with some prepara­tions still containing lindane.
    The annual market for head lice and scabies treatments is currently worth £14.4 million with recent annual growth trends in the region of 18%.

Pesticide hazards
Carbaryl is a carbamate insec­ticide which is a cholinesterase inhibitor with laboratory evi­dence of causing cancer and birth defects in test animals. It is also very readily absorbed through skin which is precisely where it is being applied for the treatment of head lice infestations(1). 
    Malathion is an organophosph­ate insecti­cide which is also a cholinesterase inhibitor and has been found to disrupt the immune system(2). 
    Permethrin and phenothrin are synthetic pyrethroids for which suspicions have recently been raised in German studies that they may be linked with leukaemia, lymphoid cancer and multiple chemical sensitivity(3).  Permethrin has already been categorised by the US-EPA as a possible human carcinogen.
    In addition, alcohol based solvents used in many formu­lations can cause allergic reactions, in particular asthma attacks, in susceptible individuals.
    In the vast majority of instances head lice infesta­tions occur on children. Less well developed immune sys­tems, underdeveloped detoxification mechanisms, rapid growth and differ­ences in diet between children and adults make children more sus­ceptible and more sensitive to the toxic effects of contaminants such as pesti­cides(4).
    In the past the monitoring, diagnosis and treatment pre­scription for head lice in UK children was carried out by school nurses. These respon­sibilities have now been removed from school nurses with­out effective replacement, and children and their parents either resort to main­stream medical practitioners, pharmacists or their own judgement to deal with the problem. The results are often inadequate and may in the long term exacerbate the problem.
    There is strong evidence that some head lice have become resistant to the pesticides in use. This has prompted rec­om­men­dations for repeat treat­ments and rotat­ing between the different products. Some products such as those con­tain­ing the pyrethroid insecti­cides do not kill all life stages of the lice. Therefore any eggs left in the hair after treat­ment will hatch in 10-14 days and reinfest the head. Similarly, ineffective treat­ments where wrong doses are applied, or lotions are applied incor­rectly can leave adults, eggs and nymphal stages alive and able to trans­mit a level of resistance to subsequent generations. Repeat treatments, rotation of chemi­cals and the use of higher doses lead to greater exposure of children to more pesticides and can also exacerbate resistance problems in louse populations(5).  The problem is that many treatments do not perform as claimed even when the instructions are followed to the letter.

Non-chemical control
As an alternative to the use of insecti­cides, physical removal of louse eggs, nymphs and adults can be extremely effective and entirely non toxic with no problems of resistance developing in the lice. The use of fine tooth combs is not a new technique, but has in the past centred on egg removal which is difficult. The organisation Community Hygiene Con­cern (CHC) has now developed a pro­gramme based on systematic removal of hatched lice which is easily done if the hair is really wet, to break the life cycle.
    CHC claims that seven year-olds can be successfully taught to detect hatched lice by wet combing(6).  They call this 'bug busting'. A child needs help to then follow through and clear the lice. The prin­ciple of the system is based on three simple facts:

• thoroughly wet lice slow down and become easy to hook off with a fine tooth comb;

• removing lice before they mature prevents them from mating and spreading;

• coordinated action by a community using this method helps prevent re-infestation.

The combing process relies on hair being thoroughly wet and tangle free. Combing is systematically carried out with a fine comb from the hair root to its end over the entire head, with any lice combed out being removed from the comb after each stroke. The process is repeated on a four day cycle over two weeks. At the end of this period all life stages of lice should have been removed and no unhatched eggs should remain in the hair.
    The CHC Bug Busting is promoted in a popular manner with cartoon charac­ters, stickers and easy to follow inst­ruc­tion cards. The Bug BusterTM kit is supplied with a fine tooth comb and CHC has designated 31 October as national Bug Buster day when they hope all schools will join in the pro­cess to stop the cycle of re-infestation(7). 
    Meanwhile the manufacturers of chemical treatments are promoting their products in preparation for the new school year. The companies are confident in the efficacy and safety of their products despite evidence to the contrary. Some companies even oppose rotation programmes to prevent resistance  as each of their products is based on single active ingredients and it is not in their commercial interest to support rotation(8). 

References
1. Cox, Caroline, Carbaryl, Part 2, Journal of Pesticide Reform, 13:2, 1993.
2. Swadener, Carrie, Low doses of malathion disrupt immune system function, Journal of Pesticide Reform, 12:3, 1992.
3. Household spray cancer link, Pesticides News 28, June 1995.
4. National Research Council, Pesticides in the diets of infants and children, National Academy Press, Washington DC, 1993.
5. Community Hygiene Concern, Information supporting early day motion 798, March 1995.
6. Ibarra, Joanna, Coping with head lice in the 1990’s, Primary Health Care 4:4, April 1994.
7. Community Hygiene Concern, Bug BusterTM Kit, CHC, 1995.
8. Some lousy facts, Chemist and Druggist, 22 July 1995.

Community Hygiene Concern can be contacted at 160 Inderwick Road, London N8 9JT. Tel. (0)181 341 7167, Fax (0)181 292 7208.