Enlarged view of Pediculus humanus capitis. Source:


General Information

Pediculus or lice, come in three varieties. The first is Pediculus humanis capitis, also known as the head louse and the second is Pediculus humanis corporis, more commmonly known as the body louse. The third type of louse is Phthirus pubis, also known as "crabs." Head, body and pubic lice have a tendency to emerge in crowded areas with low levels of personal hygiene.

Source: "Pediculosis"; Goldstein and Goldstein.

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Agent: Morphology

Pediculi are ectoparasites, meaning they live on top of their hosts instead of inside of them. They are small, six-legged insects with claws adapted to clinging onto their host's hairs or clothes. Pediculi mouth-parts are adapted to sucking the host's blood, and in the case of capitis, they are also adapted to eating dermal parts of the host's scalp, neck and eyelids. See the picture in general information, above.

gray and white tan to greyish white translucent
3 to 4 mm in length 4 to 5 mm in length 2 to 3 mm in length
Body parts
Mouth adapted to suck blood and legs adapted to grip hairs six-legged, mouth adapted for blood sucking and claws for grasping six-legged, with four legs resembling crab claws. Legs are adapted to grasp pubic hairs.

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The History of Pediculosis

Pediculosis as a human problem dates back to the earliest Homo sapiens. Researchers at the Max Plank Institute for Evolutionary Anthropology used Molecular Clock Analysis (MtDNA) to date the origins of human lice to approximately 72, 000 years ago in Africa. Expansion of lice into other parts of the world follow the expansion of modern man out of Africa approximately 50, 000 years ago.

Source: images/out_of_Africa.jpg

"Out of Africa" - The orange arrows outline the likely route of modern human beings out of Africa ~50,000 years ago.The spread of Pediculosis humanus is believed to have followed this same route.


Fun Historical Facts About Pediculosis
Ancient Remedies for Pediculosis
  • Evidence for the body louse was also recently discovered in the excavation of a fortress in Masada Israel, which was originally the storeroom for King Herod the Great. The store-room is believed to have housed soliders during the Jewish Revolt of 66 - 74 CE, which would have provided an ideal environment for a lice infestation.
  • Combing or shaving hair (Ancient Egyptians)
  • Aztec King Montezuma paid for his subjects to have their nits removed, and then he had them preserved.
  • Drinking garlic concoctions (Greece)
  • Military personel in World War One helped control the spread of the disease typhus (commonly transmitted by body lice) by bathing soldiers and washing their clothes.
  • Greek naturalist Pliny the Elder (23-79 CE) recommended destroying nits using dog's fat or eating cooked serpents.
Source: 1/c6/01/91/51/Pliny.gif


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Clinical Presentation in Humans

P. capitis:

Typically asymptomatic. Symptoms that may appear are itchiness of the neck, scalp and ears, pruritis, as well as puss in affected areas (bites). In more severe cases secondary bacterial infections can develop which may lead to febrile episodes as well as enlargement of the cervical and nucal lymph nodes.

P. corporis:

Itchiness and visible bite marks on the body and pruritis, especially around the waist and armpits. There may also be crusting and redness due to secondary bacterial infections.

P. pubis:

Itchiness in pubic areas and armpits is the most common complaint although not always a complaint. Pale blue spots at the follicular orfices may appear in the case of a prolonged infestation.



P. capitis
P. corporis
P. pubis
Clinical presentation of head, body and pubic lice. P. capitis presentation incudes brown fecal matter around the ear. The P. corporis image is the clinical presentation of pruritis due to a prolonged lice infection. P. pubis were found attached to pubic hairs in the third image. Source: DermAtlas


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Transmission, Reservoir and Vector Information

  • Human to human transmission is the only way pediculosis is transmitted. Transmission and infection are usually the results of low levels of personal hygiene
  • Tranmission of head and body lice is common where crowds of people are in close contact, such as in schools, prisons and trenches.
  • Contact with infected hair (i.e. sharing combs and/or hair brushes) can transfer head lice between individuals
  • Contact with clothing and bedding facilitates the transfer of head, body and pubic lice between human hosts
  • Sexual contact facilitates the transmission of pubic lice between individuals


Humans are the only reservoir for all human lice species. Lice do not typically survive more than 30 days without a human host.


There is no vector for pediculosis, but body lice have been known to act as vectors in the spread of other diseases such as typhus, trench fever and relapsing fever.

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Life Cycle and Incubation

Life cycle of P. capitis
The adult female will lay her eggs (7-10 per day) near the hair shaft. The egg (nit) will take approximately 8 days to develop and emerge as a nymph. The nymph will mature into an adult louse in approximately 8 days and will then begin to feed and reproduce on the scalp, neck and eyes of the infected person. Source: GIDEON -


P. corporis life cycle
P. pubis life cycle
The body louse follows a similar developmental and maturation pattern as the head louse. The adult body louse will then feed on the skin of the body of the infected individual but dwells and lays its eggs in the seams of the individuals clothing and/or bedding.   Pubic lice have a life cycle similar to both the head and body lice, although parallel the head lice more because the eggs are deposited near the base of the pubic hairs. The development and maturation of the nymph into an adult louse is similar to the development described in the diagram above.


Incubation Periods
The incubation period is the length of time the laying of the egg and the hatching of the Pediculus nymph.
P. capitis: 8 days
P. corporis: 6-10days
P. pubis: 6 - 8 days

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Diagnostic Tests

P. capitis:

Identification of louse and nits. This can be aided with the use of a fluorescent Underwood light. Careful and thorough combing can also be done to search for nits and lice. Official measure of diagnosis is the presence of nits within 6.5 mm of scalp.

  Source: "Pediculosis"; Goldstein and Goldstein.


P. corporis:

Identification of louse or nits on clothing. The adult louse may hard to identify because they move quickly across the body and clothes.

  Source: "Pediculosis"; Goldstein and Goldstein.


P. pubis:

Identification of louse or nits in the pubic and armpit areas. Identification of the adult may be difficult because of its translucense.

  Source: "Pediculosis"; Goldstein and Goldstein.

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Management and Therapy


The best preventative measure against all types of lice is to practice constistent and adequate measures of personal hygiene. This includes washing head and body hair in warm water (temperatures of greater than 130 degrees Farenheit may kill adult lice), as well as laudering clothing on a regular basis.

Other means of preventing the spread of pediculosis include not sharing personal hygeine items such as hair brushes and combs, as well as towels and unwashed clothing. One recommendation as a preventative measures for elementary-school aged children is to provide them with individual hooks for caps and coats to prevent the spread of head lice.


What to do when you do have lice:

Head Lice

The best primary treatment for headlice is a topical insecticide although drug resistance and persistent infections may require oral medications.

Topical Lotions:

Over-the-counter lotions such as 1% Permethrin cream rinse (brand name Nix) and Pyrethin (brand names Rid, A-200, Pronto and Clear) are toxic to lice yet have low toxicity and low rates of allergic reaction in mammals. Pyrethrin containing lotions are the recommended first-line treatment against head lice. Insecticide lotion available by prescription within the U.S. is 5% Malathion (Ovide).

Method of administration: Wash hair and towel dry. Cover the scalp with the lotion and let sit for ten minutes, then rinse with water. The CDC recommends repeating the treatment 7-10 days after first treatment. Malathion treatments require that the lotion sit for an 8-10 hour period before rinsing hair.


Lindane shampoo is effective but toxic, so its use is discouraged.

Oral Medications:

Ivermectin may be prescribed for a persistent and a resistant infection. A single 200 ug/kg dose should be administered, and repeated once, 2 weeks later.

Wet Combing:

Recommended for children under age two


Body Lice


Have infected individual bathe thoroughly. Be sure to wash clothes and bedding in warm water and dry in heat. Body lice can survive off of the body for 30 days so it is important to prevent re-infection by washing items that may have come in contact with infected person and his/her clothing.


Lindane lotion may be recommened (washed off after 8 hours) . Corticosteroid creams can be used for pruritic and irritated areas, applied twice daily


Pubic Lice


Remove nits with finger nails, a comb and/or tweezers. Be sure to check for recurrent infection, treat contacts such as sex partners and wash bedding and clothing in warm water.

Topical Lotions:

Permethrin, Lindane and Pyrethrin lotions may be used for treatment (see directions above). Be sure to dry and cool skin before applying lotions.

Oral Medications:

Iveremectin may be used as a second-line medication if resistance occurs. Typically use in conjunction with 5% permethrin cream. Leave cream on for 8 - 12 hours or give two doses of ivermectin (200 mcg/kg) one week apart.

Do not use ivermectin in children less than 15 kg or in pregnant or breast-feeding women.


About 1/3 of people with pubic lice will have a second venereal disease and they should be screened.

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Epidemiology and Public Health Strategies


Lice are found in countries all over the world, not excluding the most developed societies of Western Europe and the North America. Individuals from all socio-economic backgrounds can be affected by lice, although this is more true for head lice than body lice, which typically affect homeless individuals to a greater extent than individuals who have access to washing machines and hot baths. Head lice have infected elementary-aged school children in North America at epidemic proportions, and head lice infect more children than all other communicable diseases combined (6-12 million children infected each year).


Public Health Strategies

CDC recommendations for head lice outbreaks in schools:

  • Inform the school of the infestation
  • Treat all infected children for head lice - make sure to screen and track down the contacts of infected children
  • Treat house holds by treating both infected people and cleaning clothing, bedding, towels and hair brushes and combs (wash in hot water and soap).
  • Infected children may return to school 24 hours following hair treatment.
  • Make sure school nurse or other officals inform parents of outbreak.
  • When possible, avoid perpetrating stigma. Keep infected student's names confidential.


Other public health strategies for all types of lice include encouraging proper hygiene practices. Regular laundering of clothing and bedding in hot water for at least 20 minutes can kill lice. Additionally, increasing peoples accessibility to hot water can help slow the spread of Pediculosis.

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Useful Web Links

The National Pediculosis Association Inc. website:

UpToDate websource for medical journals and health information:

GIDEON: Global Infectious Disease and Epidemiology Network:

Lice Fact Sheets by the CDC:


Centers for Disease Control - Division of Parasitic Diseases. "Pediculosis." Accessed on 26 May 2005.

Cohen, Bernard. "Pediculosis capitis." Dermatology Image Atlas. Accessed on 1 June 2005.

GIDEON - Epidemiology information, images: "Pediculosis." 2005. Accessed on 26 May 2005.

Goldstein, Adam O., Goldstein Beth G. "Pediculosis". UpToDate 13.1. February 24, 2005. Accessed on 26 May 2005.

Ha, Chris. "Pediculosis Corporis." Dermatology Image Atlas. Accessed on 1 June 2005.

Kitter R, Kayser M, Stoneking M. "Molecular evolution of Pediculus humanus and the origin of clothing." Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany. Curr Biol. 2004 Dec 29;14(24):2309.

Markel, John, Krotoski. Markell and Voge's Medical Parasitology. 8th ed. Elsevier Science Health Science div, 1998.

Mumcuoglu KY, Zias J, Tarshis M, Lavi M, Stiebel GD. "Body louse remains found in textiles excavated at Masada, Israel." Department of Parasitology, The S. F. Kuvin Center for the Study of Infectious and Tropical Diseases, Hebrew University-Hadassah Medical School, Jerusalem, Israel.

The National Pediculosis Association. Accessed 22 May 2005. www.

Shahdi, Majid. "Phthrius pubis." Dermatology Image Atlas. Accessed on 1 June 2005.

Smith, Scott. D. "Pediculosis" Lecture, Stanford University. 18 May 2005.

Author: Stacy Zambrano, student at Stanford University

Spring Quarter, 2005

Human Biology 103 - Dr. Smith