Pediculosis humanus capitis

Pediculosis humanus capitis

DiseaseDisorder infobox
Name = Head lice in humans

Caption = "Pediculus humanus capitis" (♀)
ICD10 = ICD10|B|85|0|b|85
ICD9 = ICD9|132.0
DiseasesDB = 9725
MedlinePlus = 000840
eMedicineSubj = med
eMedicineTopic = 1769
MeshID = D010373

Human head lice or pediculosus humanus capitis is the infection of humans by the human head louse. It is a specific subset of the more general pediculosis, a term used for the infection of any of several species of mammal or birds by their own particular breed of louse.

Human head lice are widely endemic, especially in children. They are a cause of some concern in public health, although, unlike human body lice, head lice are not carriers of infectious disease.


Head lice ("Pediculus humanus capitis") infestation is most frequent on children aged 3-10 and their families. Females get head lice more often than males, and infestation in blacks is rare.cite web |title=Lice (Pediculosis) |publisher= |date=2005 November |work=The Merck Manual |url= | accessdate=2008-02-19 ]

Head lice are spread through direct head-to-head contact with an infested person. Body lice are spread through direct contact with the body, clothing or other personal items of a person already carrying lice. Pubic lice are most often spread by intimate contact with an infested person. Head lice occur on the head hair, body lice on the clothing, and pubic lice mainly on the hair near the groin. Human lice do not occur on pets or other animals. Lice do not have wings and cannot jump.

From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse. Full-grown lice are about the size of a sesame seed. Lice feed on blood once or more often each day by piercing the skin with their tiny needle-like mouthparts. Lice cannot burrow into the skin.

Head lice and body lice ("Pediculus humanus") are similar in appearance, although the head louse is often smaller.cite journal |author=Bacot A |title=Contributions to the bionomics of "Pediculus humanus (vestimenti)" and "Pediculus capitis" |journal=Parasitology |volume=9 |pages=228–258 |year=1917] Pubic lice ("Pthirus pubis"), on the other hand, are quite distinctive. They have shorter bodies and pincer-like claws, making them look like crabs (hence, the nickname for pubic lice: "crabs").


In order to diagnose infestation, the entire scalp should be combed thoroughly with a louse comb and the teeth of the comb should be examined for the presence of living lice after each time the comb passes through the hair. The use of a louse comb is the most effective way to detect living lice.cite journal |author=Mumcuoglu KY, Friger M, Ioffe-Uspensky I, Ben-Ishai F, Miller J |title=Louse comb versus direct visual examination for the diagnosis of head louse infestations |journal=Pediatr Dermatol |volume=18 |issue=1 |pages=9–12 |year=2001 |pmid=11207962 |doi=10.1046/j.1525-1470.2001.018001009.x |url=] In cases of children with long and curly/frizzy hair, an alternative method of diagnosis is examination by parting the hair at 2 cm intervals to look for moving lice near the scalp. With both methods, special attention should be paid to the area near the ears and the nape of the neck. The examiner should examine the scalp for at least 5 min. The use of a magnifying glass to examine the material collected between the teeth of the comb could prevent misdiagnosis.The presence of nits alone however (Fig. 4), is not an accurate indicator of an active head louse infestation. Children with nits on their hair have a 35-40% chance of also being infested with living lice and eggs.cite journal |author=Williams LK, Reichert A, MacKenzie WR, Hightower AW, Blake PA |title=Lice, nits, and school policy |journal=Pediatrics |volume=107 |issue=5 |pages=1011–5 |year=2001 |pmid=11331679 |doi=10.1542/peds.107.5.1011] If lice are detected, the entire family needs to be checked (especially children up to the age of 13 years) with a louse comb and only those who are infested with living lice should be treated.As long as no living lice are detected, the child should be considered negative for head louse infestation. Accordingly, a child should be treated with a pediculicide ONLY when living lice are detected on his/her hair (not because he/she has louse eggs/nits on the hair and not because the scalp is itchy).

Clinical symptoms

The most characteristic symptom of infestation is pruritus (itching) on the head which normally intensifies 3 to 4 weeks after the initial infestation. The bite reaction (Fig. 5) is very mild and it can be rarely seen between the hairs. Bites can be seen, especially in the neck of long-haired individuals when the hair is pushed aside. In rare cases, the itch scratch cycle can lead to secondary infection with impetigo and pyoderma. Swelling of the local lymph nodes and fever are rare. Head lice are not known to transmit any pathogenic microorganisms.

The "no-nit" policy

Despite impovements in medical treatment and prevention of human diseases during the 20th century, head louse infestation remains stubbornly prevalent. In 1997, 80% of American elementary schools reported at least one outbreak of lice.cite news
title = A modern scourge: Parents scratch their heads over lice
url =
publisher = Consumer Reports
pages = 62-63
date = February 1998
accessdate = 2008-10-10
] Because head louse infestation occurs primarily in children,cite journal
last = Mumcuoglu
first = Kosta Y.
coauthors = Meinking, Terri A; Burkhart, Craig N; Burkhart, Craig G.
year = 2006
title = Head Louse Infestations: The "No Nit" Policy and Its Consequences
journal = International Journal of Dermatology
volume = 45
issue = 8
pages = 891–896
publisher = International Society of Dermatology
pmid = 16911370
url =
doi =10.1111/j.1365-4632.2006.02827.x
] government efforts to eradicate head lice have focused on establishing policies that minimize head lice transmission at child care facilities. The "no-nit" policy is one such attempt. This policy requires the immediate dismissal of a louse-infested child from a school, camp, or child-care setting until all lice, eggs, and nits have been removed from the child. Although the basic premise of a no-nit policy is simple, in practice it is composed of at least three sub-policies that are not mutually inclusive:

*Routine inspection of children for lice, eggs, or nits
*Immediate exclusion of children found to have lice, eggs, or nits
*Barring the child's return until subsequent inspection finds the child to be free of lice, eggs, and nits

The no-nit policy is popular with health authorities in the United States, Canada, and Australia. A 1998 survey revealed that almost all (96%) American school nurses send home infested students upon discovery.cite journal
author = Price JH, Burkhart CN, Burkhart CG, Islam R
title = School nurses' perceptions of and experiences with head lice
journal = The Journal of school health
volume = 69
issue = 4
pages = 153–8
year = 1999
month = April
pmid = 10354985
url =
accessdate = 2008-10-10
] A majority (61%) of those nurses also prevent return of treated students to school if they are not (also) nit-free. A similar percentage (60%) felt that "forced absenteeism of any child who has any nits in their hair is a good idea."

Although the no-nit policy has the appearance of a simple and popular tool against pediculosis transmission, its implemention has been opposed by a number of health researchers and organizations.cite journal
last = Frankowski
first = Barbara L.
coauthors = Leonard B. Weiner, the Committee on School Health, the Committee on Infectious Diseases
year = 2002
month = September
title = Head Lice: American Academy of Pediatrics Clinical Report
journal = Pediatrics
volume = 110
issue = 3
pages = 638-643
publisher = American Academy of Pediatrics
issn = 0031-4005
pmid = 12205271
url =;110/3/638
accessdate = 2008-10-10
] cite journal
last = Frankowski
first = Barbara L.
year = 2004
month = September
title = American Academy of Pediatrics guidelines for the prevention and treatement of head lice infestation
journal = The American Journal of Managed Care
volume = 10
issue = 9
pages = S269-S272
pmid = 15515631
url =
accessdate = 2008-10-10
] cite web
url =
title = Pediculosis in the School Community: Position Statement
accessdate = 2008-10-10
author = National Association of School Nurses
year = 2004
month = July
publisher = National Association of School Nurses
location = Silver Spring, Maryland
] Opponents argue that enforcement of no-nit policies have not significantly reduced head louse infestation in school settings, and that the risks and disadvantages of the no-nit policies outweigh their associated benefits.

These opinions have influenced public policy such that, as of|2008|lc=on, some government agencies recommend "against" a no-nit policy. In Australia, for example, the National Health and Medical Research Council states that infested children need not be sent home upon discovery. And treated children can return with nits so long as they are lice-free. [Citation
title = Staying Healthy in Child Care: Preventing infectious diseases in child care
author = National Health and Medical Research Council
publisher = Commonwealth of Australia
year = 2005
month = December
edition = 4th
url =
] Similarly, the California Department of Public Health now advocates a "no-lice" policy that does not immediately exclude infested children, nor prevent them from returning with nits. The California policy does, however, advocate routine screening for the presence of live lice.cite web
url =
title = Guidelines on head lice prevention and control for school districts and child care facilities
accessdate = 2008-10-10
author = Infectious Diseases Branch, Division of Communicable Disease Control
year = 2007
format = pdf
publisher = California Department of Public Health
pages = 1-4


The most common symptom of lice infestation is itching. Excessive scratching of the infested areas can cause sores, which may become infected.

Body lice can be a vector for louse-borne typhus, louse-borne relapsing fever or trench fever, although this is not a concern for head lice per se, which is therefore more of a purely cosmetic problem.


The number of cases of human louse infestations (or pediculosis) has increased worldwide since the mid-1960s, reaching hundreds of millions annually.cite journal
last = Gratz
first = Norman G.
title = Human lice: Their prevalence, control and resistance to insecticides. A review 1985-1997
url =
format = pdf
publisher = World Health Organization
location = Geneva, Switzerland
date = 1998
accessdate = 2008-01-02
] There is no product or method which assures 100% destruction of the eggs and hatched lice after a single treatment. However, there are a number of treatment modalities that can be employed with varying degrees of success. These methods include chemical treatments, natural products, combs, shaving, hot air, and silicone-based lotions.

Lice on the hair and body are usually treated with medicated shampoos or cream rinses. Nit combs can be used to remove lice and nits from the hair. Laundering clothes using high heat can eliminate body lice. Efforts to treat should focus on the hair or body (or clothes), and not on the home environment.

Some lice have become resistant to certain (but not all) insecticides used in commercially available anti-louse products. A physician or pharmacist can prescribe or suggest treatments. Because empty eggs of head lice may remain glued on the hair long after the lice have been eliminated, treatment should be considered only when live (crawling) lice are discovered.


Examination of the child’s head at regular intervals using a louse comb allows the diagnosis of louse infestation at an early stage. Early diagnosis makes treatment easier and reduces the possibility of infesting others. In times and areas when louse infestations are common, weekly examinations of children, especially those 4–13 yrs old, carried out by their parents will aid control. Additional examinations are necessary, if the child came in contact with infested individuals, if the child frequently scratches his/her head, or if nits suddenly appear on the child’s hair. Keeping long hair tidy could be helpful in the prevention of infestations with head lice.In order to prevent new infestations, the hair of the child could be treated with 2–4 drops of concentrated rosemary oil every day, before he/she leaves for school or kindergarten. The oils can be combed through the hair using a regular comb or brush.cite journal| last =Mumcuoglu | first =Kosta Y. | coauthors =R. Galun, U. Bach, J. Miller, and S. Magdassi | title =Repellency of Essential Oils and Their Components to the Human Body Louse, Pediculus humanus humanus | journal =Entomologia Experimentalis et Applicata | volume =78 | issue =3 | pages =309–314 | publisher =The Netherlands Entomological Society | location =Wezep | date =1996 ] Clothes, towels, bedding, combs and brushes, which came in contact with the infested individual, can be disinfected either by leaving them outside for at least 3 days or by washing them at 60°C for 30 minutes. An insecticidal treatment of the house and furniture is not necessary.


About 6-12 million people, mainly children, are treated annually for head lice in the United States alone. High levels of louse infestations have also been reported from all over the world including Israel, Denmark, Sweden, U.K., France and Australia.cite journal| last =Burgess | first =Ian | title =Human Lice and their Control | journal =Annual Review of Entomology | volume =49 | pages =457–481 | publisher =Annual Reviews | date =January 2004 | url = | doi =10.1146/annurev.ento.49.061802.123253 |pmid=14651472 ] cite journal| last =Mumcuoglu | first =Kosta Y. | coauthors =Barker CS, Burgess IF, Combescot-Lang C, Dagleish RC, Larsen KS, Miller J, Roberts RJ, Taylan-Ozkan A. | title =International Guidelines for Effective Control of Head Louse Infestations | journal =Journal of Drugs in Dermatology | volume =6 | pages =409–14 | date =2007 |pmid=17668538 ] Normally head lice infest a new host only by close contact between individuals, making social contacts among children and parent child interactions more likely routes of infestation than shared combs, brushes, towels, clothing, beds or closets. Head-to-head contact is by far the most common route of lice transmission.The number of children per family, the sharing of beds and closets, hair washing habits, local customs and social contacts, healthcare in a particular area (e.g. school) and socio economic status were found to be significant factors in head louse infestation . Girls are 2-4 times more frequently infested than boys. Children between 4 and 13 years of age are the most frequently infested group.cite journal| last =Mumcuoglu | first =Kosta Y. | coauthors =Miller J, Gofin R, Adler B, Ben-Ishai F, Almog R, Kafka D, Klaus S. | title =Epidemiological studies on head lice infestation in Israel. I. Parasitological examination of children | journal =International Journal of Dermatology | volume =29 | pages =502–6 | publisher =International Society of Dermatology | location =Palm Coast, FL |date =1990 | url = | doi =10.1111/j.1365-4362.1990.tb04845.x |pmid=2228380 ]

The United Kingdom's National Health Service, and many American health agencies [] [] [] , report that lice "prefer" clean hair, because it's easier to attach eggs and to cling to the strands.

Vectorial capacity

Head lice ("Pediculus humanus capitis") are not known to be vectors of diseases, unlike body lice("Pediculus humanus humanus"), which are known vectors of epidemic or louse-borne typhus ("Rickettsia prowazeki"), trench fever ("Rochalimaea quintana") and louse-borne relapsing fever ("Borrellia recurrentis").

ee also

*Head louse
*Body louse
*Crab louse
*Treatment of human head lice


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