head louse

 

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Head louse
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Order: Phthiraptera Suborder: Anoplura Family: Pediculidae Genus: Pediculus Species: P. humanus
Binomial name
Pediculus humanus Linnaeus, 1758
Trinomial name
Pediculus humanus capitis Charles De Geer, 1767
Synonyms
Pediculus capitis (Charles De Geer, 1767)

The head louse (Pediculus humanus capitis) is one of the many varieties of sucking lice specialized to live on different areas of various animals.

As the name implies, head lice are specialized to live among the hair present on the human head and are exquisitely adapted to living mainly on the scalp and neck hairs of their human host. Lice present on other body parts covered by hair are not head lice but are either pubic lice (Pthirus pubis) or body lice (Pediculus humanus humanus).

Description

The adult head louse resembles a miniature ant that appears flat when viewed from the side through a strong magnifying glass. Head lice have a head, thorax and abdomen with six legs,(which makes them insects) but their two front legs are very large in order to grab onto the hair shafts. Head lice are tan to greyish-white in color. Headlice are easy to notice in blonde or ginger hair,because yellow and orange are light colours. Human lice do not feed on the blood of other animals, only humans.

Symptoms

The most common symptom is itching of the scalp, caused when the louse bites through the skin to feed on blood. Other symptoms include irritation caused by the louse's saliva, insomnia, adenopathy, hair loss in massive infestations and psychological disturbs(mainly because of the associated stereotype), also excessive scratching may cause bleeding of the scalp, which may increase the risk of microbial infection.

Head lice (Pediculus humanus capitis) are not responsible for the spread of any disease[1], unlike body lice (which is a different species,Pediculus humanus humanus).

Treatment

Main article: Treatment of human head lice

Treatments proven by medical research

Shaving the Head

Shaving off all the hair is a viable solution.[2] This can be performed alone using mirrors to see all sides of the head, although it is easier to have someone else help with the procedure. A completely shaven head is not necessary, the hair only needs to be cut to 1 inch or less.

Shaving the head gives the lice little to grasp to stay attached to the head. The main reason for cutting is to lower the temperature of the scalp. Lice primarily stay in the areas of hair that are warm and dark. Girls generally have longer hair and you will find that the lice stay at the base of a ponytail, nape of the neck, or behind the ears. Cutting the hair very short will cause an insufficient ambient temperature for lice to live in. While effective, some patients may find the hair removal aesthetically unappealing which is why many turn to other cures, typically requiring some form of chemical to be applied.

Natural solutions

Natural solutions permeate the Internet and are also sold in some retail stores. Their effectiveness is not always supported by research studies. Natural treatments are being sought by concerned caretakers due to the possible harmful effects that are caused by pesticide-based head lice solutions. Natural solutions are generally made up of ingredients that are grown or produced naturally by plant or floral life. When using these type of treatments be aware of possible allergic reactions.

Mechanical removal of lice or viable louse eggs by combing

A recent British study [3] suggests that combing wet hair with a special comb, known as "bug busting" or "wet combing," may be significantly more effective than use of insecticides, and can get rid of lice within 1-2 days of infestation.

Regular use of metal headlice combs will prevent major cases of infestation. Suggested use is once every week or two after being in close contact with many people.

A special finetooth comb that can pick out lice is used. The space between the teeth of the comb should be no more than 0.3 mm (0.01 inch). Plastic combs are effective for very short-term use, but the spacing between the teeth will quickly spread out after repeated usage. Metal combs, being inflexible, are more effective for multiple uses.

Following are instructions for wet combing:

• First, comb through wet hair with an ordinary comb to relieve knots and tangles.
• Apply conditioner or olive oil to make it easier to comb the hair with the fine-toothed comb.
• Comb through every bit of hair, pulling the comb from the scalp to the hair ends. After every comb-through, examine and rinse the comb. Use an old toothbrush or nailbrush to remove eggs and nits from the comb and flush the eggs down the sink. Comb through the entire head and scalp at least twice, flushing away any lice found. Afterwards, rinse the conditioner out (or shampoo out any oil).
• Repeat the aforementioned steps every two or three days to catch any new lice that have hatched since the previous combing.
• Repeat the aforementioned procedure until lice are not found for at least two treatments in a row. The Pharmaceutical Society of Australia recommends treating with comb and conditioner every two days until lice are not found for ten consecutive days. A reminder that the itch symptoms may persist without the presence of head lice up to a week after eradication.

One may find that a cold shower is best before wet combing. The cold water slows the insects, making for easier removal.

Malathion

Malathion works as well as other agents used to kill lice. Malathion must be left on for at least eight hours for it to work. It is applied to dry hair until the scalp and hair are wet and thoroughly coated. If lice are found 7-10 days after treatment, treat again with the same or different medication. The alcohol in malathion lotion and the terpenoids may cause stinging. Opinion differs as to its safety with pregnant or breastfeeding women. Considered safe by some, other organizations such as La Leche League have disagreed with this since breast milk may contain whatever the mother has eaten or come in contact with.

Lindane

Although lindane may work as well as other insecticide based agents, its use is limited by its potential neurotoxicity. It is applied, for only four minutes, to wet the hair and skin or scalp of the affected area and surrounding hairy areas. Treatment may be repeated after seven days if necessary. Lindane should be avoided in pregnancy and breastfeeding. If it must be used in pregnancy, it should only be used once.

Permethrin

Permethrin may work better than lindane, though most trials were done before permethrin was widely used and resistance to the drug developed. It is used as 1% creme rinse left on for 10 minutes. If the first application fails to kill the eggs (that is, if young hatching lice are found using a suitable detection comb) a second treatment is indicated, usually seven days after the first treatment. Undertreatment in this situation could contribute to the development of resistance to the drug. There is no role for a third application, as this will contribute to resistance and is not likely to be effective. Permethrin has not been studied in pregnancy.

Pyrethrins

Pyrethrins are used as a 0.33% shampoo or mousse, by applying enough to thoroughly wet the hair and leaving it on for 10 minutes. All pyrethrum products that conform to the US Food and Drug Administration criteria for use in humans require a second application after 7-10 days, to ensure treatment of lice emerging from eggs that have not been killed by the first application. Pyrethrins work as well as permethrin.

Insecticide resistance

In recent years, resistance to the above-mentioned insecticides has become an important factor in treatment failure.

Resistance has been confirmed as affecting permethrin treatments. Similar resistance is suspected for pyrethrins but is not yet confirmed. Resistance to lindane has been identified in the Netherlands, Israel, Malaysia, and Denmark but has not yet been confirmed in the United States. Malathion is apparently resistance-free, except in the United Kingdom and France.

If a patient has adequately used over the counter products but still has lice, the most reliable prescription treatment is malathion. This product is less easy to apply than a shampoo because it is a freeflowing liquid and must be left on for at least eight hours. It has a pungent odor due to a high level of monoterpene components in the essential oils that were included to mask the odour of malathion. The monoterpenes contribute much of the pediculicidal and ovicidal activity of the product. Evidence for activity of malathion is good. About 2-3% of malathion applied to the scalp is absorbed through the skin. In some cases, lindane may be prescribed instead of malathion. Evidence for lindane’s effectiveness is relatively poor, and lindane is about 4-10 times more toxic than malathion. A high proportion of lindane applied to the skin is absorbed through the skin.

Unverified treatments

Herbal treatments

Herbal treatments (including tea tree oil) are sometimes used to treat head lice. A small number of studies have been undertaken to evaluate their efficacy. [4], [5]

One trial, involving 143 louse infested children, compared a herbal oil treatment (containing coconut, anise and ylang ylang oils in unspecified concentrations) against a treatment containing a combination of insecticides (0.5% permethrin plus 0.25% malathion, synergised with 2% piperonyl butoxide). It found no significant difference in elimination rates between the two treatments (60/70 with the herbal product v 59/73 with insecticide solution). Although the study found no detectable toxic effects of either solution, certain herbal oils may have a potential for toxic effects. [6]

Aromatherapy

Aromatherapy has been frequently used to treat for lice, but this has not been confirmed as a viable treatment.

Use in Archaeogenetics

Lice are also important in the field of Archaeogenetics. Because most "modern" human diseases have in fact recently jumped species from animals into humans through close agricultural contact, and also given fact that Neolithic human populations were too scattered to support contagious "crowd" diseases, lice (along with such parasites as intestinal tapeworms) are considered to be one of the few ancestral disease infestations of humans and other hominids. As such, analysis of mitochondrial lice DNA has been used to map early human and archaic human migrations and living conditions. Because lice can only survive for a few hours or days without a human host, and because lice species are so specific to certain species or areas of the body, the evolutionary history of lice reveals much about human history. It has been demonstrated, for example, that some varieties of human lice went through a population bottleneck about 100,000 years ago (supporting the Single origin hypothesis), and also that hominid lice lineages diverged around 1.18 million years ago (probably infesting Homo erectus) before re-uniting around 100,000 years ago. This recent merging seems to argue against the Multi-regional origin of modern human evolution and argues instead for a close proximity replacement of archaic humans by a migration of anatomically modern humans, either through inter-breeding, fighting, or being more fit to use available resources.

See also

• Pediculosis
• Nitpicking
• Olive oil
• Delphinium

External links

• Treating head lice - an article from the British Medical Journal
• What to do if your child has head lice from Seattle Children's Hospital
• Extinct humans left louse legacy
• Lice from MayoClinic
• Headlice.org FAQ from the National Pediculosis Association

Head Lice policy statement from American Academy of Pediatrics

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