PREVENTING HEAD LICE

 

NEW APPROACHES TO COMBATING RESISTANT HEAD LICE

The head louse is a blood-feeding ectoparasite insect found only in human hair. Adult head lice have cigar shaped bodies.        r They are about as long as a sesame seed.  Their colors range in appearance for translucent and/or nearly colorless to almost totally black.  All healthy lice have some coloration because blood in the gut  shows through the thin outer layer of the body either as a dark red or black streak. This combination of darker and lighter areas helps to break up the outline of the louse and make it more difficult to see when aligned with a strand of hair or even against the skin.

Head lice lay eggs that they attach to hairs close to the scalp. Each egg is laid singly and carefully deposited onto the the hair, where it fixed with a droplet of cement produced by the accessory glands of the female louse. The cement covers the base of the eggshell and encircles the hair shaft before sitting hard, a few seconds after deposition.  The glue like material holds the eggshell into position for months after the embryo has completed development and the nymphal louse emerges from the shell.  These persistent empty egg shells are known as nits, but in common terms the work "nit" has come to be applied to any louse egg, viable or otherwise--which can be confusing for diagnosis and control.  In their position close to the scalp, the eggs remain at a relatively constant temperature and humidity, with the scalp acting as a perfect incubator.

Soon after emergence from the egg the young louse takes its first blood meal from its human host and continues to do so at regular intervals for the rest of its life.  It is not known how often lice feed, but it has been suggested that they take at least six blood meals each day.

Female lice are able to mate and lay eggs about 24 hours after completing their final molt, so from the hatching of an egg in one generation through to the start of laying of eggs for the next generation take a minimum of 10 days.

People can suffer from head louse infestation at any age, but in reality only a small segment of our society is at risk.  There are no recent prevalence data from any western country, but the general opinion among most health care workers is that prevalence of head louse infestation has increased in recent years.

How lice are transmitted is a major concern for most parents and caregivers.  Authorities agree tha the primary route of transmission is via head-to-head contact between close associates.  Mechanical transfer of lice by inanimate objects (fomites) such as combs and hairbrushes, hats, scarves, headphones, cuddly toys, and sporting gear such as batting helmets has been implicated in popular literature.  But there has not been a publication offering a clear demonstration of scientific evidence of this method of infection.  In most circumstances, this mode of transmission is unlikely.  In the case of others, the probability is limited by the physical vulnerability of the lice.  Two analyses of louse prevalence and distribution were unable to confirm that any method other than direct head-to-head contact could account for the cases involved.  While it is occasionally possible that lice might pass to another person via fomites, the likely frequency of such an event is epidemiologically insignificant compared with the more probable route of transmission by head-to-head contact.  For example, in a household it is theoretically possible that a louse might be dislodged from one person's head onto a sofa or other soft furnishing.  Another person sitting on the same sofa later in the day might, in turn, pick up that louse.  However, in most families it is more likely that a physical contact between the two people would result in lice transferring from one to the other.

In most communities, girls are more likely than boys to be found with head lice.  The reasons for this are often misunderstood.  It is widely assumed that because more girls have long hair, hair length plays some part in the epidemilogy.  Although head lice live among head hair, they have no particular interest in it other than as a substrate on which to lay their eggs, as a support to grasp as they clamber around their host's head, and as a shelter from host view.

The diagnosis of head louse infestation, although seemingly simple in principle, is more difficult than most people think.  Unlike most other infectious conditions, it is theoretically possible to identify and treat all active cases and effectively prevent further transmission.  However, not only are lice relatively diffficult to find but even the most widely employed methods are fairly inefficient.

A positive diagnosis can be made only by finding a living louse.  Louse eggs that have died or been killed by pediculicides retain an appearance similar to that of living louse eggs and often cannot be distinguished even by an experienced observer using a microscope until dehydration has caused shrinkage of the contents.  Eggs or empty eggshells attached to the hairs can persist for months after an infestation has been treated successfully; so they offer no surety as to whether an infestation is active.

The most efficient diagnostic method is to use a detection comb that can lift out the smallest first instar nymphs from among the hairs.

Many people think that itching is a good indication of evidence of infestation.  While itching is a symptom that does occur with pediculosis, it takes some time for the immune response to develop and for itching to arise--possibly several weeks or even months in some cases.

Combing has long been used as a component of therapy or as a treatment in its own right.  In the days before the advent of chemical pediculicides, combing out lice and their eggs was the only form of treatment available.  For most people, a recognized pediculicide is the most attractive treatment option.  With a pediculicide, they have the opportunity to cure an infestation quickly with a minimum of effort.  Most treatments used in the United States involve over-the-counter products containing either permethrin or pyrethrum extract synergized with piperonyl butoxide.  Application of a pediculicide should not be made unless one or more live lice have been found.  When they are used, the treatment should be thorough not only to ensure cure, but also to avoid the development of resistance to the pediculicides.

MANAGEMENT OF HEAD LICE

1. Check carefully for living lice, preferably using a plastic, fine-toothed comb to ensure that an infestation is active. This should be a part of routine care anyway, and if carried out weekly, new infestaions can be found before they have time to become established.
2. Once living  lice have been found, other members of the household should be checked.
3. If a pediculicide is being used, each person with lice should be thoroughly treated with an appropriate product ensuring that the entire scalp and hair are saturated.
4. It is important to read the product instructions completely and follow them exactly.
5. After washing off the preparation, the caregiver should perform nit (empty shell ) removal, especially since it is a school requirement.
6. Regardless of whether nit combing is performed, follow-up checks should be made using a fine-toothed plastic comb during the week after treatment.
7.After the treatment regime has been completed, regular follow-up checks should be performed by scalp examination and combing with the fine-toothed plastic comb at least once a week This allows families to avoid further infestatation from outside contacts who have not been treated.
 

Information obtained from " New approaches to combating RESISTANT head lice" . Provided through and educational grant from BAYER Consumer Care Division.