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| '''For patient information click [[{{PAGENAME}} (patient information)|here]]'''
| | #REDIRECT[[Pediculosis capitis]] |
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| {{CMG}}
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| {{SI}}
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| == Overview ==
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| [[Image:Pediculus humanus var capitis.jpg|left|thumb|250px|Head louse]] | |
| The head louse (Pediculus humanus capitis) is one of the many varieties of sucking lice specialized to live on different areas of various animals.
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| 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).
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| '''''Related Key Words and Synonyms:'''''
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| Pediculus humanus capitis (peh-DICK-you-lus HUE-man-us CAP-ih-TUS)
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| == Epidemiology and Demographics ==
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| Having head lice is very common. However, there are no reliable data on how many people get head lice in the United States each year.
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| Occasionally, head lice may be acquired from contact with clothing (such as hats, scarves, coats) or other personal items (such as brushes or towels) that belong to an infested person. Preschool and elementary-age children, 3-11, and their families are infested most often. Girls get head lice more often than boys, women more than men. In the United States, African-Americans rarely get head lice. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.
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| == Risk Factors ==
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| Anyone who comes in close contact (especially head-to-head contact) with someone who already has head lice is at greatest risk.
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| == Screening ==
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| == Pathophysiology & Etiology==
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| '''Etiologic agent:'''
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| Pediculus humanus capitis, the head louse, is an insect of the order Anoplura and is an ectoparasite whose only host are humans. The louse feeds on blood several times daily and resides close to the scalp to maintain its body temperature.
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| They are most commonly found on the scalp, behind the ears and near the neckline at the back of the neck. Head lice hold on to hair with hook-like claws found at the end of each of their six legs. Head lice are rarely found on the body, eyelashes, or eyebrows.
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| '''Life cycle:'''
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| [[Image:Lice LifeCycle.gif|left|frame|Life cycle of Head lice]]
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| The life cycle of the head louse has three stages: egg, nymph, and adult.
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| *Eggs: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the scalp '''1'''. They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.
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| *Nymphs: The egg hatches to release a nymph '''2'''. The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult head louse, but is about the size of a pinhead. Nymphs mature after three molts ('''3''', '''4''') and become adults about 7 days after hatching.
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| *Adults: The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white '''5'''. In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s head. To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.
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| <gallery>
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| Image:Nit.gif|Egg on a hair shaft
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| Image:Nymph.jpg|Nymph form
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| Image:Adult louse.jpg|Adult louse
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| </gallery>
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| '''Transmission:'''
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| The main mode of transmission is contact with a person who is already infested (i.e., head-to-head contact). Contact is common during play (sports activities, playgrounds, at camp, and slumber parties) at school and at home.
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| Less commonly,
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| *Wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons, recently worn by an infested person.
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| *Using infested combs, brushes, or towels.
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| *Lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person.
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| == Diagnosis ==
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| [[Image:Hair lice.jpg|right|Searching for lice in hair]]
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| An infestation is diagnosed by looking closely through the hair and scalp for nits, nymphs, or adults. Finding a nymph or adult may be difficult; there are usually few of them and they can move quickly from searching fingers. If crawling lice are not seen, finding nits within a 1/4 inch of the scalp confirms that a person is infested and should be treated. If you only find nits more than 1/4 inch from the scalp (and don't see a nymph or adult louse), the infestation is probably an old one and does not need to be treated. If you are not sure if a person has head lice, the diagnosis should be made by your health care provider, school nurse, or a professional from the local health department or agricultural extension service.
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| === History and Symptoms ===
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| *Tickling feeling of something moving in the hair.
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| *Itching, caused by an allergic reaction to the bites.
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| *Irritability.
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| *Sores on the head caused by scratching. These sores can sometimes become infected.
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| [[Image:H nit.jpg|left|Nit drawing]]
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| {{clr}}
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| '''A: Head Lice: Nit'''
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| Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the scalp. They are 0.8 mm by 0.3 mm, oval and usually yellow to white. Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the scalp.
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| [[Image:Adult female louse.jpg|left|Adult female louse]]
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| {{clr}}
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| '''B: Head Lice: Adult female louse'''
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| The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white. In persons with dark hair, the adult louse will appear darker. Females lay up to 8 nits per day. Females are usually larger than males.
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| == Treatment ==
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| '''Shaving the Head'''
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| Shaving off all the hair is a viable solution. 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.
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| 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.
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| '''Natural solutions'''
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| Natural solutions permeate the Internet and are also sold in some retail stores. Their effectiveness is not always supported by research studies.
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| 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.
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| '''Mechanical removal of lice or viable louse eggs by combing'''
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| [[Image:Head lice comb.jpg|left|thumb|lice comb]]
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| Louse CombA recent British study 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.
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| 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.
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| 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.
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| Following are instructions for wet combing:
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| *First, comb through wet hair with an ordinary comb to relieve knots and tangles.
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| *Apply conditioner or olive oil to make it easier to comb the hair with the fine-toothed comb.
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| *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).
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| *Repeat the aforementioned steps every two or three days to catch any new lice that have hatched since the previous combing.
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| *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.
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| *One may find that a cold shower is best before wet combing. The cold water slows them down making for easier removal.
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| '''Herbal treatments'''
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| 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.
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| 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.
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| '''Aromatherapy'''
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| Aromatherapy has been frequently used to treat for lice, but this has not been confirmed as a viable treatment.
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| === Pharmacotherapy ===
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| ==== Acute Pharmacotherapies ====
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| '''Malathion'''
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| 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.
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| '''Lindane'''
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| 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.
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| '''Permethrin'''
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| 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.
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| '''Pyrethrins'''
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| 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.
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| ==References==
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| #http://www.cdc.gov/ncidod/dpd/parasites/lice/factsht_head_lice.htm
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| #http://www.dpd.cdc.gov/dpdx/HTML/HeadLice.htm
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| #http://en.wikipedia.org/wiki/Head_louse
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| == Acknowledgements ==
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| The content on this page was first contributed by: C. Michael Gibson, M.S., M.D.
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| Initial content for this page in some instances may have came from [http://www.wikipedia.org Wikipedia] and [http://www.askdrwiki.com AskDrWiki]
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| Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources:
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| 1.[http://www.diseasesdatabase.com/index.asp The Disease Database]
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| 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3
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| 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7
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| '''List of contributors:'''
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| Pilar Almonacid
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| == Suggested Reading and Key General References ==
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| == Suggested Links and Web Resources ==
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| == For Patients ==
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