CABI - Biocontrol News and Information 21(2) June 2000 News

Biocontrol News and Information

March 2001, Volume 22 No. 1

IPM Systems

This section traditionally deals with IPM techniques compatible with biocontrol, particularly in agriculture. As a diversion this quarter,
we consider the community health sector, and how action at community level is bringing about reductions in pesticide use for head lice control.

Bringing Head Lice Control up to Scratch

Head lice (Pediculus capitis) are not a danger to health; they neither serve as vectors nor do they generally cause direct harm or disease. Yet their management is a headache for public health workers worldwide. Here, we look at why they are perceived as such a problem, reasons for the limits to the success of current control measures, and how the limits are being addressed.

Head lice are wingless, parasitic insects adapted to living solely on the head hair of their human hosts. The claws on the ends of their legs are adapted for grasping hair shafts. They feed exclusively on blood, taking several blood meals a day, and die of dehydration and starvation within 2 days if removed from the head. Head lice do not jump, fly or swim but they can move swiftly along hair shafts. Transfer to a new host is almost exclusively by direct contact with infested hair. Nymphal stages tend to stay on the head where they hatch, while adults (particularly males) tend to migrate where possible to maximize out-crossing.

Why Scalps Crawl

Head lice are rather less contagious than the common cold and far less serious in terms of health. Yet although revulsion to them may be groundless it has been the basis for most management strategies. It is particularly in schools, where reports of waves of infestations are commonplace, that most control efforts are focused - often needlessly and unsuccessfully in the view of Richard Pollack (Harvard School of Public Health, USA). Control measures fail, he argues, because they are designed to appease the public rather than deal with the problem, and instead they tend to burden the child. He points to exclusion from school of allegedly infested children and mass screening as pointless measures. He argues that quarantining has not been shown to be effective (by the time head lice are detected the child may have had them for a month or more), and that more than half of the children identified as infested may be misdiagnosed.

Exclusion of children from school because they have 'nits' is a widespread practice in the USA, although no distinction is made between live eggs and inviable/hatched eggs. Such exclusion policies are discouraged by the American Academy of Pediatrics and the (US) National Association of School Nurses. Pollack argues that most reported outbreaks of head lice in schools are no such thing: most 'infestations' he examines show no evidence of current (or past) infestation, normal debris on the hair or scalp frequently being mistaken for lice or eggs. In schools reporting more than 50% prevalence amongst its pupils, Pollack found actual prevalence rarely exceeded 1%, and sometimes he identified not a single case. A study of specimens associated with diagnosis of infestation submitted by health care workers and lay people found that less than 50% were head lice stages. Ian Burgess (Cambridge Medical Entomology Centre, UK) says that diagnosis of real infections has been consistently poor, and often based on paranoia and misunderstanding. He cites a survey of school nurse managers attending the human louse control management courses in the UK in 1982. It found that 50% of the health professionals interviewed (all of whom had been involved in screening for head lice in schools) had never seen a live louse, and relied on the presence of nits to confirm an infestation. A report by the 'Stafford Group' for the Consultants in Communicable Disease Control (CCDCs) in the UK criticized both high-input screening and heavy-handed exclusion policies. They argued that the former has no measurable impact on infestation levels (although there are as yet no reliable data for these). They also pointed out that exclusion policies do little to reduce spread in schools, and only serve to increase the stigma of head lice infestations.

The UK health authorities used to cover the cost of routine screening of schoolchildren for head lice, but discontinued this practice in the early 1980s declaring it to be largely ineffective. Failure to establish an alternative management strategy, though, has led parents in the UK to blame a perceived increase in head lice incidence in schools on the withdrawal of school nurse inspections. Ian Burgess notes that in most districts most children had been screened less than once a year, if that. The little data collected after inspections stopped suggested that prevalence dropped, if anything, after screening ceased! Although Belgian health workers have demonstrated that inspection based on finding nits gives a high level of false positives, they and the UK nonprofit organization Community Hygiene Concern (CHC) both found that visual inspection also misses a large number of light, but contagious cases. In the absence of firm current data the Stafford Group suggest that prevalence has not increased, only public awareness - or perhaps over-awareness?

Conditions Right for Combing

In Richard Pollack's view, there is no conceivable need to apply insecticides for head lice within schools (and neither are such ancillary measures as cutting hair, bagging clothes and not using shared protective sports equipment justified; indeed, the latter carries far greater risk than a head louse infestation.) However, many are uncomfortable with the notion of parasites they can actually see or feel crawling about on their heads or their children's, so even if control cannot be justified on health grounds, there is still a demand for it. In some cases, too, infestations are so chronic and severe that treatment is justified on health grounds. But what or when to treat is not obvious to the non-expert. Many health authorities and other extension services in the USA, the UK and elsewhere disseminate information by various means (leaflets, videos, websites, etc.), but quality is variable and sometimes only increases confusion. Clear guidance is needed.

The first step is finding out whether or not someone is infested. There are strong advocates for inspecting dry and wet hair, and the methods may be appropriate in different situations. Both, though, rely on combing with a fine-toothed comb to locate any lice or nits. Recent advances in this technique have been due to the work of CHC, who in 1988 set up a community development programme, Bug Busting, to help parents of schoolchildren in the UK acquire head louse detection skills. They had already established the value of combing wet hair with a plastic fine-toothed comb for this purpose. Wet detection combing is now the most widely-recommended method in the UK for confirming presence or absence of active head lice. The CHC protocol comprises methodical combing of washed, still-wet, well-conditioned hair. The moisture temporarily immobilizes lice, which can be comfortably combed out and then inspected. Emphasis is also placed on tracing infested contacts. CHC have conducted a series of case studies that have demonstrated the value of wet Bug Busting to detect low-level infestation, and thus recommend it for parents anxious to know if a child is infested. However, Ian Burgess argues that dry combing is equally accurate and is routinely practised by the Cambridge Medical Entomology Centre. The method has been used in several trials. He points out it is more practical (particularly where large numbers of heads are examined) because it is quicker and less messy.

For either method, generally no indication is given of how long should be spent on combing, and without adequate guidance, detection combing by inexpert hands can lead to both false negatives and false positives. Richard Pollack advises using the presence of live lice or viable eggs as the sole basis to confirm an infestation, but notes that recognition of eggs as viable requires suitable magnification and some training. Moving objects maybe also erroneously identified as head lice. CHC suggest that if parents are in doubt, 'combings' can be taken to a professional for identification, but say that most parents, given the right information and combs, can identify them without this recourse.

In the USA, a different detection policy has been developed for determining whether an infestation is active or a treatment is working. The America Head Lice Information Center (AHLIC) educate health professionals and parents that eggs are firmly attached at an angle to one side of the hair shaft, and cannot be removed by blowing or flicking. Once nits have been confirmed to be present, an active infestation is diagnosed by a two-step process: all eggs are removed, then the hair is inspected to see if new ones appear.

No Certain Solutions

The question of quite how to kill the head lice presents the next dilemma. The conventional approach is a synthetic insecticidal application or series of applications. A variety of products is registered in different countries, commonly pyrethroids and malathion but others include carbaryl or lindane. There are two problems with such treatments. The first is the growing antipathy of the public to synthetic pesticide use, with children a particular concern; the second is the perception that the insecticide treatments 'don't work'. Together these have led to disenchantment. There are reports of side-effects for all the synthetic insecticides currently registered, although proponents argue that the doses used in head lice products are so low as to be reasonably safe when used properly.

There is evidence from a number of countries for the development of resistance to the most commonly used pesticides, the pyrethroids and malathion, and Ian Burgess says that places they have surveyed in the UK in the past 6 years have double or even treble resistance. Resistance is likely to increase in incidence and intensity with time, but how often do treatments really fail? One common misconception at least partly to blame for perceived failure is the expectation that an insecticide treatment provides an instant fix. This is reinforced by labels on many products proclaiming that they kill both lice and eggs in a single application, which most do not, and certainly not reliably. Eggs are resistant to many of the registered products. A second application (recommended in the UK by the Stafford Group to be made on day 8) is intended to mop up the lice that hatch after day 1. Some of the products provide a limited residual effect, designed to kill hatching nymphs. Egg survival may be the first sign of resistance, but it is unclear how far widespread treatment failure is due to this. However, the residual action of current products, so hatching nymphs are exposed to lessening levels of insecticide, is likely to enhance resistance development.

Less contentious is the adverse impact of poor application of products, which is often based on poor understanding of the life cycle of the head louse. Instructions may not be followed precisely. Too little may be used (products are perceived as expensive), and/or the treatment may not be followed up where users believe that all the head lice have been killed by the first treatment. Another 'wave' of head lice appearing some weeks post-treatment is often blamed on a 'new' infestation (acquired from another person) rather than the more likely explanation of a resurgence from surviving eggs and lice, or misdiagnosis (with only dead or hatched eggs present). Joan Sawyer says that AHLIC call it 'the myth of reinfestation'. Misunderstandings about insecticide action are also reflected in attempts to apply prophylactic treatments.

When synthetic insecticides appear to fail, people may turn to other treatments, and increasingly to 'alternative' remedies in the misguided belief that because they are 'natural' they are inevitably safe. Yet amongst various herbal remedies widely touted are ingredients such as rosemary oil, which is known to induce abortion. Even products generally considered safe for some uses on humans, such as tea tree oil and lavender, may be applied at doses well in excess of those recognised as safe doses on children's heads. Research on essential oils suggests that they act as contact nerve poisons in the same way as synthetic insecticides. The efficacy of both synthetic and natural insecticides relies in part on their lipid soluble characteristics, as this facilitates their entry into the body (through either insect cuticle or human skin). Children are more sensitive than adults to the toxic effects of pesticides because they have incompletely-developed detoxification mechanisms and are growing rapidly. The active ingredients in most natural remedies are monoterpenes, which as a class are widespread in plants and are also found in some insects, and there is every reason to suppose that they will also be subject to resistance development in time. For example, there has been interest in coconut oil in the USA, and it may have efficacy as a treatment against head lice populations there. However, this effect may not be sustainable, and may not be mirrored in countries where coconut oil is commonly present in hair products already. The use of sublethal levels of monoterpene compounds (as are likely to be present, for example, in tea tree oil shampoo) will enhance resistance development.

The lack of certainty about the efficacy and toxic effects of synthetic and natural insecticide treatments is creating a vacuum, but the challenge is to come up with an effective alternative.

Look to Our Roots

Grooming and 'nit picking' are practised by our ape relatives, and were once part of human hygiene, a routine task undertaken by older siblings or parents (and still remembered by some of us, although not necessarily fondly). Perhaps it is a casualty of modern life, perhaps the advent of insecticide treatments led to its demise, but since 1995 its metamorphosis into Bug Busting as a remedy has occurred. CHC developed wet detection combing into a treatment, which depends on systematic removal of head lice to break the life cycle. The Bug Busting method follows a prescribed protocol, twice weekly for two weeks. It is based on three tenets:

'coated' lice move more slowly and so are more easily removed by combing
removing lice before they mature prevents them spreading and reproducing
co-ordinated community action helps decrease the rate of reinfestation

CHC produced a Bug Buster kit containing full instructions and the necessary comb, which was piloted in 1995 and commercialized in 1996. An improved model with a modified comb became available early in 1999. Currently, the London School of Hygiene and Tropical Medicine (LSHTM) is conducting a randomized controlled trial comparing the effectiveness of the Bug Buster kit with insecticidal medication.

A number of organizations in the USA, including the National Pediculosis Association (NPA) and the American Head Lice Information Center (AHLIC) promote combing together with other measures for head lice control. However, the emphasis US head lice policies placed on children being nit (rather than active lice) free means that mechanical methods to resolve infestation have taken a different path from those in the UK, with an emphasis on nit as well as active lice removal. AHLIC have produced a book and a video, 'Head Lice to Dead Lice', which uses humour to get across the message. The programme is based on a five-step battle plan, and includes the optional use of (a pyrethroid) insecticide. Instructions are given on the correct technique for smothering hair with olive oil (which is left on overnight under a rubber cap to smother the lice by blocking the spiracles), the correct days and method for combing to remove nits and lice, and advice on nit picking on dry hair.

A modified 'no nit' policy was included in a programme encouraging combing as a method of head lice removal that was developed by the extension service of the University of Nebraska at Lincoln. Barbara Ogg says that a major problem with head lice in the local community was exacerbated by health professionals giving different recommendations on control to parents, who became confused. A head lice task force to formulate a policy was formed that included health professionals (school nurses, public health nurses, university educators), the state medical entomologist and child care programme administrators (from the health department). The policy was announced before the beginning of the school year in autumn 1999. Parents were urged to check their children's hair before school started and school nurses inspected children during the first week of term, and again mid-term and after the Christmas break (January 2000). School nurses agreed that they would not recommend products or treatment methods not proven to be effective against head lice; this was a major achievement because there were many advocates for mayonnaise and other home remedies. The University of Nebraska Cooperative Extension provided a videotape and fact sheets that were sent home with children.

The focus of the recommendations promotes combing with a long-toothed metal comb over all other activities as the 'alternative' method of control to remove nits. Where time is limited, people are encouraged to nit comb above all else. Barbara Ogg says that this really was a community collaboration and worked well over a trial period. Head lice have not been eliminated, but (and arguably more importantly) the school system is now seen to have a more proactive policy and to be taking the necessary steps to minimize the problem. An acceptable level of success was being maintained one year on: in the year 1999-2000, head lice cases had dropped to 2000 from a pre-programme level of 6700 (presumably based on the presence or absence of nits). This programme set itself realistic goals, and undertook active education at the community level to achieve these.

Testing Time

Advocates consider that bug busting offers an affordable head louse remedy, which is re-usable, does not require insecticides, clears lice that are resistant to insecticides, and promotes self reliance in head louse control. Detractors have some reservations about details of current protocols, but more significantly consider that the bug busting method is simply too time-consuming and demanding in commitment to be of value at a community level. They also point to social constraints: some children's hair is not readily combed, and bug busting can cause pain to them. Some parents are unable or unwilling to comply with the recommended protocol. Others may become over-keen on bug busting and family conflict can ensue. All these are issues which proponents of the method recognise and have sought to deal with. CHC have specifically developed methods for combing different hair types and instructions for these are included in their Bug Busting kit. Joan Sawyer of AHLIC argues that far from resenting the time that combing takes, parents and health professionals are increasingly aware of the even greater cost in time and money of relying on poor information and ineffective or dangerous pesticides.

The success of a bug busting programme may depend on how effectively the message is disseminated through the community and, in the long term, on the degree to which the momentum can be maintained once the initial wave of enthusiasm has subsided. Recognizing this, CHC resource designated Bug Busting days on 31 January and 31 October each year in the UK. They say that success relies to a large extent on the understanding by schools of their role in generating coordinated, informed effort followed by a top-up each Bug Busting day. Getting the message across would be helped by including head lice in the primary/first school science curriculum (in the UK, the national science curriculum at this level currently does not include insects with incomplete metamorphosis - a no-nits policy with a difference).

Although some good short-term results have been reported, success levels vary. How far, too, is initial success simply a reflection of the focus on controlling head lice rather than the method employed? Until recently, there have been few attempts to quantify the success of the method in comparison with other (insecticide) treatments. The mechanisms of long-term sustainability of the CHC programme are currently undergoing evaluation in addition to being included in the 3-year full-scale evaluation of head lice treatments by the London School of Hygiene and Tropical Medicine begun in 1999. Other studies comparing insecticide treatments and bug busting in the UK have recently published results. These varied in design; for example, in using professionals to apply treatments, or working through parents, and the results are far from clear cut. However, a trial in Bristol which looked at insecticide resistance found 87% and 64% failure for permethrin (pyrethroid) and malathion, respectively. A randomized controlled trial in North Wales, which compared the efficacy of two malathion treatments with CHC Bug Busting (using the 1996 comb) found 78% and 38% success, respectively. Arguments over the trials and their interpretation have focused not only on trial designs and interpretation of results, but also on whether it is justifiable to recommend a head lice management strategy based on either method. However, CHC are encouraged by the North Wales results, which showed 38% success using the more laborious 1996 comb without initial demonstration, or the back-up they provide. They point out that skill at Bug Busting grows with familiarity, while lice resistance to insecticides increases with continued use. A knowledge of Bug Busting, they argue, is empowering to a community, while it does not benefit from dependence on failing insecticides.

Teasing Out the Snags

What, then, are the current constraints to bug busting and what are the keys to making it work? Areas to consider include: (a) communicating the message; (b) length of treatment; (c) hair lubricants and how to use them; and (d) combs and how to use them.

According to Ian Burgess, Bug Busting is a well-known and often-tried method, which can and should work. When it fails, it does so for a number of reasons, probably most importantly, he says, because many users do not understand why they are doing what they are doing. They follow the method, as they understand it, and are surprised and disappointed if it fails. Flawed information from unreliable sources and word-of-mouth are at least partly to blame, but in order to get the message across it may be over-simplified. On the other hand, CHC maintain that more than 80% of people they deal with are able to understand and follow their instructions, and achieve good results. Clear consistent information is crucial to this, and technical backstopping, as provided by their Bug Busting days, is important for reinforcing the message and contributes to the sustainability of the approach.

Most protocols (including CHC's) involve combing twice-weekly for 2 weeks; a total of four or at most five treatments. AHLIC is rare in advising a longer treatment period of 3 weeks, with six combings over this period. The more common 2-week period to remove live lice makes the method seem manageable, and CHC and AHLIC concur that this is an essential consideration. It is not much point developing a protocol that is too onerous for people even to attempt; but equally, advocate a protocol that frequently fails and you quickly lose credibility. Consideration of the head louse life cycle indicates that two weeks does not allow much of a margin for error: miss a few lice, and you will soon be back to square one. AHLIC say that in devising their strategy they were determined to create a protocol that covered all possible errors, worked consistently for people unskilled at nit-picking, and did not overtax the family. The criterion for success that they used to evaluate the protocol during the research phase was that the entire family should be louse and nit free 10 days after completion of the programme. The CHC protocol includes a follow-up Bug Busting 4 days after the last treatment; if live lice are found, treatments are repeated. The UK Department of Health advises a wet combing check 3-5 days after using an insecticidal product. But even if a protocol seems foolproof, it won't be: there will be a few who will not follow it strictly for whatever reason, and a few will make mistakes. An important message to get across, especially in societies that expect sure-fire solutions, is that bug busting is not a guaranteed fix, but it is a skill which improves with practice. AHLIC's experience is that people are willing to admit mistakes and try again.

There are some robust disagreements about hair lubricants and their use. Olive oil is favoured by Ian Burgess and Joan Sawyer, as it is fairly easily emulsifiable (and therefore washed out afterwards), non-irritant and emollient (and so can be used on sufferers with eczema and psoriasis). Burgess notes that it is available in the UK as a pharmaceutical preparation. Sawyer describes it as "cheap, healthy and healing, with the only side-effect of gorgeous hair"! However, hair conditioner has the edge as a familiar and attractive product to use, which CHC say makes it more immediately acceptable. They suggest that even the most stout-hearted parent might be put off by the thought of trying to control and comb small slippery children dripping oil all over their soft furnishings. Although there are disagreements over which is the more effective for allowing lice/nits to be extracted, and also over safety (and lack of testing for this use), all parties report good success rates.

Protocols rarely suggest how long combing should take either for detection or for treatment, although the University of Nebraska-Lincoln programme stresses that nit combing should take precedence over all other anti-louse activities. Burgess suggests that detection combing may take 30 minutes, treatment combing several hours. Given normal family pressures, this time is likely to be hard to find, and it is understandable that bug busting programmes do not set out draconian regimes that will probably be ignored, if not put people off altogether. However, if combing is not performed adequately, the method is bound to fail. Successful combing is a technique which needs to be demonstrated, and this is addressed in information products produced by the programmes discussed in this article. CHC point out that the time for bug busting depends on hair type and length but agree that poor explanation of how to comb by some information sources contributes to failure, which is then used to discredit bug busting as a whole. CHC has produced a demonstration video, recommended by many UK health authorities, to introduce Bug Busting. In this and printed resources, they demonstrate clearly how to go about detection and treatment combing for different hair types and lengths.

Finally there is disagreement over the optimal comb design, and this is perpetrated in many leaflets, websites and other information products which do not clearly distinguish between detection and treatment combs, or lice and nit combs. CHC raised funding to research the issue. It built on the results of field tests made in the first half of the 20th century to select the precise slant on the leading edge of the new plastic Bug Buster comb that most effectively removed even newly hatched lice close to the scalp. Burgess agrees that a blunt-tipped plastic comb with appropriately and evenly spaced teeth works best for active lice removal. Both CHC and Burgess say that the use of inappropriate combs is a widespread reason for failure. In the USA, metal toothed nit combs are more popular, and these work particularly well for removing nits. Apparent discrepancies in advice may well be a reflection of the UK focus on breaking the lice cycle by removing hatched lice but not worrying about nits, and the US focus on removing nits as well as lice so children can return to school.

Putting Heads Together

In conclusion, IPM of head lice may be struggling a little at the moment, but there is an urgent need for it to succeed. Ian Burgess argues that failure in head lice management begins at the primary level: stakeholders from health professionals at all levels through public and community workers of all description to affected individuals and families would rather not know about head lice, or have to deal with them. In addition, conflicting and confusing advice on how to deal with head lice is widespread. Barbara Ogg says that the success of the University of Nebraska-Lincoln programme was rooted in forming a task force so all 'experts' spoke with one voice, a view firmly supported by John Simpson, chairman of the 'Stafford Group'. Clear, consistent high-quality information based, as CHC emphasize, on sound science and practical approaches, is crucial. Parents need to be aware of the likely reasons if control fails, so they can consider how to revise their practice to optimize the chances of success the next time. If this option is not available, they are more likely to abandon bug busting for some other remedy.

The clear message coming through is that combing for head lice management can and does work under a variety of protocols, and this is very positive. Its sustainability at the community level is being assessed. However, the approach taken by agricultural IPM of integrating a variety of approaches to help overcome the shortcomings of individual components has limited application currently. Whether new non-pesticidal methods will become available remains to be seen, but other techniques would be useful. Ian Burgess observes that potential methods in the pipeline based on a non-neurotoxic physical approach could fill one niche.

Contacts/information:
American Head Lice Information Center
Email: sawyermac@aol.com
Website: http://www.headliceinfo.com

Ian Burgess,
Medical Entomology Centre, Cambridge Road,
Fulbourn, Cambridge CB1 5EL, UK
Email: ifburgess.medentcent@tesco.net
Fax: +44 1223 882690

Community Hygiene Concern (CHC),
160 Inderwick Road, London N8 9JT, UK
Email: bugbusters2K@yahoo.co.uk
Fax: +44 20 8292 7208
Website: http://www.nits.net/bugbusting

The National Pediculosis Association
Website: http://www.headlice.org/

Richard J. Pollack,
Laboratory of Public Health Entomology, Dept. Immunology & Infectious Diseases,
Harvard School of Public Health,
665 Huntington Avenue, Boston,
MA 02115-6021, USA
Email: rpollack@hsph.harvard.edu
Website: http://www.hsph.harvard.edu/headlice.html

University of Nebraska-Lincoln
Website: http://www.ianr.unl.edu/ianr/lanco/nviro/pest/lice.htm

John Simpson,
Public Health Laboratory Service,
Communicable Disease Surveillance Centre South East,
Lower Ground Floor, 40 Eastbourne Terrace,
London W2 3QR, UK
Fax: +44 207 725 3460

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