Head lice problems with kids
Head lice infestation introduction
Head lice infestation is a major problem in the United States, thoughout Europe and Asia. The problem is particularly common in schoolchildren. There are many treatments but whatever approach is used, head lice can be a persistent or recurring nuisance.
A study of different techniques for removing lice would suggest that there is little common ground except perhaps on the importance of combs and combing whether these be used as stand alones or as adjuncts to other treatments.
Nature and incidence of head lice
Lice are external parasites of warm-blooded animals. Humans support two types of louse, each adapted to survival in a separate niche involving a different part of the body.
The head louse has been present among humans since their earliest origins. It has evolved in a highly specialised way for survival in the environment provided by the haired human scalp, to the extent that its survival requires it to spend the whole of its life-cycle on a human host.
The female is required to mate before each egg is laid (so as to lessen the risk of the egg being infertile). Lice are vulnerable to inbreeding, so outbreeding is a requirement for survival, and the urge to dispersal is strong in both sexes. Transmission is by contact between the hair of different heads. Head lice intermingle as a community, and one louse may spend its day on several heads.
Head lice are much more prevalent than body lice in the developed and developing countries. A reduction in their incidence in the post-war period through use of insecticides (DDT, HCH), has been followed by evidence of an increasing upsurge in recent years.
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Occurrence of head lice
Lice are more common among children than adults, and among females than males in any age group. The age group most in danger is that spanning kindergarten age to 14 or 15 years, while 4-6 year olds are the group most likely to catch head-lice. In the developed world, head-lice are most prevalent among suburban and rural children, largely of middle-class parentage. The same person can catch lice repeatedly. Head lice exhibit a preference for clean hair.
Need to deal with head lice
If not dealt with, head lice affect the carrier adversely.
The characteristic feature of the group to which human head-lice belong is blood-sucking. When feeding, the louse pierces the scalp with its mouth-parts, pumping in saliva and drawing out a mixture of saliva and blood. While humans are not born with the ability to react to such bites, repeated contact with the sensitizing allergens contained in the saliva creates an allergic reaction, so that each further bite evokes an itchy reaction. Wounds produced in the scalp by scratching in response to itches can become inflamed and infected. If lousiness is allowed to persist, the wounds can develop an extreme condition, whose successful treatment can not be assured.
A population of head-lice which is neglected will reach a steady state, where the death-rate equals the birth-rate, and some two hundred lice of all post-ovum stages are present. About five thousand eggs are laid each month, and the head eventually becomes grey with drifts of empty egg shells. Such a population, when present for some months, is enough to produce the symptoms of pediculosis capitis. The child becomes itchy, tired, dull and sullen. The bright child becomes average, and the average child stupid.
Although they can be shown to act as transmitters of typhus and fevers in the laboratory, head-lice are not responsible for the transmission of disease in the field. Lice are considered highly unlikely to transmit AIDS.
Life cycle of the head louse
The life cycle of the head louse falls into three distinct phases, egg, nymph and mature louse.
Louse eggs, some 0.5 to 0.8 by 0.3 millimetres, are usually laid at the base of hairs, within 0.5 mill of the scalp, where they hatch after seven or eight days. During incubation, the hair will grow away from the scalp by some two millimetres. The eggs are firmly glued to the hair, usually one only per hair, by a clear, quick-setting substance secreted by the female. Live eggs are usually camouflaged by being the same colour as the scalp. By virtue of the complicated construction of the egg shell, the ovum is extremely well protected, even against the action of insecticidal substances.
The nymph resembles the adult louse in behaviour, and in physical terms apart from size. In some ten days after hatching it is mature.
Mature head lice are 2 to 4 millimetres long, shun light, and move swiftly - 10 to 20 centimetres a minute - in all lateral directions, clinging to and crawling through the hair with their six claws. Otherwise transparent, headlice camouflage themselves by darkening, after feeding, to the colour of the skin and hair of the host, in the range from blond to black.
The empty egg-shell is called a nit. It is a brilliant snowy white, and remains firmly glued to the hair. The hair grows at a rate of some one centimetre per month, carrying any nits attached to it away from the scalp.
Detection of head lice
The presence of head lice is signalled by itching in response to bites, or by visual evidence.
Unless desensitised to their bites by repeated exposure, the host will begin to itch when bitten sufficiently often for the body to learn to react. This can take as long as three months the first time the host catches lice.
The detection of head lice by inspection during the first stages of an infection can be a tedious operation. Head lice can betray their presence through casts and faeces deposited on pillows. They will show up in water used for hair-washing, and on a pale surface when dry hair is brushed and combed over it. The most reliable method of detection is combing of the wetted hair with a suitably designed detector comb.
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Prevention of head lice
The only practicable approach to prevention of head lice appears to be attentive (rather than perfunctory) hair care by normal means, carried out in awareness that head lice may occur. The belief that brushing and combing reliably results in damage to lice in the hair such as to render them incapable of reproduction has been shown to be false. The use of insecticides prophylactically, even via their residual effect on the hair after treatment, is discouraged on grounds of unnecessary human exposure to toxicity, and of risk of encouraging high tolerance of and resistance to the insecticide among head lice.
General approach to dealing with head lice
Because of their high mobility, head lice are most sensibly dealt with at the level of the individual and of the community simultaneously, when the treatments reinforce one another in terms of eradication and prevention of re-infestation. The activities of detection, treatment and prevention are today shared in differing degrees between public health authorities and individuals.
It is acknowledged that early detection is crucial to the treatment of infection by head lice, as only early treatment can contain it.
Treatment of head lice
The objective in treating a case of head louse infestation must be to free the host of eggs, nymphs and lice, as well as of nits or empty shells, for the continued presence of the latter can only serve to confuse later diagnosis. Further requirements are that the treatment be easy to carry out, be inexpensive, and that side-effects be kept to a minimum.
Early treatments for head lice were mostly manual, and involved clipping the hair short and removing lice, eggs and nits or empty egg-shells with fine tooth combs. Earlier chemical means achieved suffocation of lice and eggs with various oils, fats and greases. Combinations of vinegar, kerosene, oils, shampooing and combing have been employed.
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Elimination of head lice and nymphs
Head lice and nymphs can be removed with the aid of suitably designed combs, or killed by use of an insecticidal treatment.
Elimination of eggs
Elimination of eggs by manual methods can be reliably achieved only with the aid of a comb which satisfies a range of narrowly defined operating requirements, which in turn impose demanding design and engineering requirements. The evidence currently available suggests that only combs with metal teeth remove eggs satisfactorily when used in isolation.
If the glue binding the egg to the hair is dissolved, the requirements placed on a comb for removal of the egg become less demanding. The Sacker family, manufacturers of the highly regarded metal nit-comb of that name, are reported as believing that the crux of head louse control revolves round the discovery of something that will destroy the cement used by the louse to glue on the nits, since the lice can be removed by washing and combing. An agent purporting to dissolve this glue has recently been introduced to the market.
The alternative approach to dealing with head lice eggs is to employ chemical means to kill them. However, evidence suggests that pediculicides currently available are at best only 70% to 80% ovicidal when used safely ' so that repeat application is required after a suitable interval to ensure that nymphs hatched from surviving eggs are killed. The vehicle substance in some insecticidal formulas has been observed to aid the removal of nits.
Objections to use of insecticides
Two sets of objections to insecticidal treatment of head lice have been raised, that they can be expected to become ineffective as pediculicides, and that they bring risk of toxicity to the subject and to the environment.
"Any insect population which is systematically subjected to a particular conventional insecticide will eventually evolve resistance to the insecticide". Resistance by head lice to the DDT and HCH groups has already developed. A study suggests that rotating two insecticide groups does not postpone resistance, double resistance emerging at the same time whether rotation is made, or one chemical is used until it fails and is then replaced by the other.
Objection on grounds of toxicity to the use of insecticides in the treatment of head lice is summarised in the statement that "all conventional pesticides are potentially hazardous substances". In this view, both the host and the environment are considered to be at risk. As both mature head lice and nymphs can be dealt with by non-chemical means, the observation on toxicity of pediculicides currently available has led to the suggestion of a need "to develop an egg-killing treatment which does not contain any conventional insecticide".
Removal of treaded eggs and nits
While removal of dead eggs and nits from the hair can be considered irrelevant from the point of view of prevention of further infection, it is advocated for control and cosmetic reasons.
It is possible, after treatment with an ovicidal insecticide, for a louse embryo to undergo total paralysis without being killed. Such an embryo will continue to develop, though it can never hatch, and the egg can retain its living appearance for as long as a month. Diagnosis of a fresh infection in a follow-up examination can be confused by the presence of such an egg. Although it will have moved away from the scalp through normal hair-growth, it can still be mistaken for a viable egg, since viable eggs have been found to be laid occasionally some distance from the scalp.