Introduction
Background
Lice are ectoparasites that live off of their human hosts. Lice feed on human blood after piercing the skin and injecting saliva, which causes pruritus. Lice are able to survive away from their human host. However, they will die of starvation within 10 days of removal from their human host.
Ye ugle, creepin, blastit wonner,
Detested, shunned by saunt an' sinner,
How daur ye set your fit upon her,
Sae fine a lady.
Gae somewhere else and seek your dinner,
On some poor body.
— Robert Burns (Scotland, 1759-96), written after seeing a louse move across a lady's bonnet during the church sermon
Pathophysiology
The head louse (Pediculus humanus capitis) and the body louse (Pediculus humanus corporis) are of similar size and can interbreed. The pubic louse (Pthirus pubis), or "crab," is morphologically distinct from the other two. Pubic lice primarily infest the anogenital area, but they can infest eyelashes, eyebrows, beards, the axillae, and (rarely) the scalp.
The head louse, Pediculus humanus capitis, has an elongated body and narrow anterior mouthparts. Body lice look similar but lay their eggs (nits) on clothing fibers instead of hair fibers.
The head louse, the most common of the 3 species, is spread by close physical contact and by shared fomites (eg, combs, brushes, hats, scarves, bedding).
The adult head louse can live 5-6 weeks on the scalp, but it survives only 1-2 days away from its host. The adult female louse lays eggs, called nits, at the base of the hair shaft. Nits hatch in 8 days if they are kept near body temperature, and mature in another 8-9 days. Cooler temperatures retard both hatching and maturation.
Nit from Pediculus humanus capitis on a hair.
Most infestations involve 10-20 adult lice.
Frequency
United States
Pediculosis capitis is found most commonly in school-aged children, typically in late summer and autumn. Reported prevalence ranges from 10-40% in US schools. Hair length and personal cleanliness are not factors in infestation rates.
Mortality/Morbidity
- Body lice can be vectors for disease such as epidemic typhus and relapsing fever.
- Lice infestation more often causes social embarrassment and isolation of the patient, rather than medical complications.
- One study estimated, that in 1998, 12-24 million days of school were lost secondary to the no-nit policies in place.
Race
- Lice infestation affects all races.
- Reported incidence of lice infestation in African Americans in the United States is relatively less than in whites.
Sex
Prevalence of lice infestation is higher in females than in males.
Age
All age groups are affected.
- Head lice infestation is common among young school-aged children in North America.
- Pubic lice are more common in adults than in children.
Clinical
History
Patients may come to the ED after discovering lice or nits, which indicate infestation. Sometimes, children are brought to the ED for evaluation when concerned parents learn about a case of lice at their child's school or daycare center.
- Many lice infestations are asymptomatic.
- Pruritus and associated secondary skin infections (with regional adenopathy) may occur.
Physical
Pruritus may lead to secondary excoriations that produce skin infection and regional lymph node enlargement. However, such findings are nonspecific.
- Pediculosis capitis
- Although head lice are found on any part of the scalp, they most commonly are found in the postauricular and occipital areas.
- Eggs depend upon body warmth to incubate. Nits are attached to hair shafts within 3-4 mm of the scalp by a sticky substance.
Nit on a hair. Note the thin, translucent cement surrounding the hair shaft. Photo courtesy of David Shum, MD, Division of Dermatology, University of Western Ontario.
- Since hair grows approximately 10 mm/mo, the distance of nits from the scalp can be used to estimate the duration of infestation.
- Pediculosis corpus
- Body lice can be found in any area of the body, although they tend to avoid the scalp, except at the margins.
- Since nits are laid in the host's clothing (especially along inner seams of clothing), they usually are not found on the hair as with head lice and pubic lice.
- Pediculosis pubis
- Pubic lice can be found in hairy areas throughout the body but prefer the perineum and pubic areas.
- An exception is prepubertal children, in whom eyebrows and eyelashes are common sites of infestation.
The pubic louse, Pthirus pubis, is identified by its wide crablike body.
Causes
- Pediculosis usually is caused by contact with an infested person.
- Fomites, such as clothing, headgear, combs, and hairbrushes, may play a role in the spread of lice.
More on Lice |
 Overview: Lice |
| Differential Diagnoses & Workup: Lice |
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| References |
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References
Benzyl alcohol lotion 5% [package insert]. Atlanta, GA: Sciele Pharma Inc; 2009. [Full Text].
Burgess IF, Brown CM, Lee PN. Treatment of head louse infestation with 4% dimeticone lotion: randomised controlled equivalence trial. BMJ. Jun 18 2005;330(7505):1423. [Medline].
Burgess IF, Lee PN, Matlock G. Randomised, controlled, assessor blind trial comparing 4% dimeticone lotion with 0.5% malathion liquid for head louse infestation. PLoS ONE. Nov 7 2007;2(11):e1127. [Medline].
American Academy of Pediatrics. Pediculosis. In: Pickering, LK ed. 2003 Red Book: Report of the Committee on Infectious Diseases. 26th ed. Elk Grove Il: AAP; 2003:463-467.
Brown S, Becher J, Brady W. Treatment of ectoparasitic infections: review of the English-language literature, 1982-1992. Clin Infect Dis. Apr 1995;20 Suppl 1:S104-9. [Medline].
Clore ER, Longyear LA. A comparative study of seven pediculicides and their packaged nit removal combs. J Pediatr Health Care. Mar-Apr 1993;7(2):55-60. [Medline].
Drugs for head lice. Med Lett Drugs Ther. Jan 17 1997;39(992):6-7. [Medline].
Gilbert DN, Moellering RC, Jr., Samde MA. The Sanford Guide to Antibiotic Therapy 1998. Dallas, Tex: Antimicrobial Therapy Inc; 1998:94-95.
Halpern JS. Recognition and treatment of pediculosis (head lice) in the emergency department. J Emerg Nurs. Apr 1994;20(2):130-3. [Medline].
Hart G. Risk profiles and epidemiologic interrelationships of sexually transmitted diseases. Sex Transm Dis. May-Jun 1993;20(3):126-36. [Medline].
Heukelbach J, Feldmeier H. Ectoparasites--the underestimated realm. Lancet. Mar 13 2004;363(9412):889-91. [Medline].
Huynh TH, Norman RA. Scabies and pediculosis. Dermatol Clin. Jan 2004;22(1):7-11. [Medline].
Ibarra J, Hall DM. Head lice in schoolchildren. Arch Dis Child. Dec 1996;75(6):471-3. [Medline].
Klaus S, Shvil Y, Mumcuoglu KY. Generalized infestation of a 3 1/2-year-old girl with the pubic louse. Pediatr Dermatol. Mar 1994;11(1):26-8. [Medline].
Kristensen M, Knorr M, Rasmussen AM, et al. Survey of permethrin and malathion resistance in human head lice populations from Denmark. J Med Entomol. May 2006;43(3):533-8. [Medline].
Lebwohl M, Clark L, Levitt J. Therapy for head lice based on life cycle, resistance, and safety considerations. Pediatrics. May 2007;119(5):965-74. [Medline].
Mumcuoglu KY, Meinking TA, Burkhart CN, et al. Head louse infestations: the "no nit" policy and its consequences. Int J Dermatol. Aug 2006;45(8):891-6. [Medline].
Yoon KS, Gao JR, Lee SH, et al. Permethrin-resistant human head lice, Pediculus capitis, and their treatment. Arch Dermatol. Aug 2003;139(8):994-1000. [Medline].
Further Reading
Keywords
lice, louse, nits, pediculosis capitis, head lice, pediculosis corporis, body lice, pediculosis pubis, pubic lice, crabs, Pediculus humanus capitis, Pediculus humanus corporis, Pthirus pubis, lice infestation
