AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

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

Lice are ectoparasites that feed on human blood after piercing the skin and injecting their saliva. The 3 types of lice infestations are pediculosis capitis (head lice), pediculosis corporis (body lice), and pediculosis pubis (pubic lice, ie, crabs).

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, 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. Most infestations involve 10-20 adults. 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.

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.

Race

• All races are affected.
• Reported incidence in African Americans in the United States is relatively less than in whites.

Sex

Prevalence is higher in females than in males.

Age

All age groups are affected.

• Head lice infestation is common among young school children in North America.
• Pubic lice are more common in adults.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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.
  • 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.

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.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

Desquamated epithelial cells (dandruff)
Seborrheic scales
Hair root sheath casts

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Tests

• The diagnosis rests on the observation of eggs (nits), nymphs, or mature lice.
• • Observing lice is difficult. Nymphs and mature lice, despite being unable to hop or jump, can move rapidly through dry hair.
  • Mature lice are 3-4 mm long (approximately the size of a sesame seed). Nits are much smaller—about 1 mm. The pubic louse is about the same length as the head or body louse but has a wider body.
  • The use of a magnifying glass and knowing where to look for lice (based upon the biology of each species as described above) assists diagnosis.
• Nits are fluorescent under a Wood light.
• Unlike dandruff and hair root sheath casts, nits are cemented to the hair and are difficult to remove.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Emergency Department Care

• Patient therapy consists of 2 parts: medications and environmental control measures (see Further Outpatient Care).
• Consider providing medical treatment to all persons who have contact with patients who are infested, especially sexual partners.
• In the treatment of body lice, medications are less essential than environmental measures.
• • Many infectious disease authorities recommend only environmental measures to treat body lice.
  • Patients with body lice should have infested clothing removed and destroyed.
  • If medical therapy is prescribed as an adjunct to environmental measures, one of the therapies listed below may be selected.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

The goal of therapy is to eliminate the mite. Family members and sexual partners should be treated.

Drug Category: Scabicidal agents

Treatment options include permethrin 1% and 5% cream, pyrethrin products, lindane, mercuric oxide ointment 1%, and 0.5% malathion in 78% isopropanol.

For treatment failures, ivermectin—given orally in doses 1 week apart—may be used in the nonpregnant or nonbreastfeeding woman and in children weighing more than 15 kg.

A recent study (Burgess, 2005) reported efficacy of 4% dimeticone lotion (a silicone-based lotion believed to disrupt the louse's ability to manage water).

Drug Name	Pyrethrin products (A200 Pyrinate, End Lice, RID Mousse, RID Shampoo)
Description	Used in the treatment of Pediculus humanus infestations. The parasite absorbs the drug where its nervous system is stimulated, causing seizure and death to the parasite.
Adult Dose	Apply as a cream rinse, allow to remain in place for 10 min, then rinse off; a second application (using the same technique) is recommended 7-10 d after initial therapy to destroy nits effectively
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity; chrysanthemum allergy
Interactions	None reported
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Do not apply to eyes, face, or mucous membranes

Drug Name	Lindane 1% (Kwell)
Description	Stimulates the nervous system of the parasite, causing seizure and death. Second-line treatment recommended for patients who fail to respond to permethrin or pyrethrin. Not very safe in children due to transcutaneous absorption leading to neurotoxicity. Overall, permethrin is a safer choice.
Adult Dose	Apply as cream rinse after shampooing with nonmedicated shampoo; allow to remain in place for no more than 4 min, then rinse thoroughly
Pediatric Dose	Infants and children: Apply thin film topically over entire body including hairline, neck, scalp, temple, and forehead, leave on 6-8 h before washing off with water; may repeat in 1 wk if necessary; not to exceed 30 g/application
Contraindications	Documented hypersensitivity; neonates, patients with an acutely swollen skin, those diagnosed with Norwegian scabies
Interactions	Oil-based hairdressings may increase toxicity of lindane
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Caution with history of seizures or keratinization/ichthyosis disorders; do not apply to eyes, face, or mucous membranes

Drug Name	Mercuric oxide ointment 1%
Description	Used to treat louse infestation of eyelashes. Inspect eyelids for nits and remove them mechanically.
Adult Dose	Apply to eyelashes qid for 14 d
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity
Interactions	None reported
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Avoid direct contact with eye

Drug Name	Malathion (0.5%) in 78% isopropanol (Ovide Lotion)
Description	Recently approved (1999) by US FDA to treat head lice. Irreversible cholinesterase inhibitor that is hydrolyzed (and therefore detoxified) rapidly by mammals but not by insects; ovicidal and pediculicidal. Binds to hair and provides some residual protection after therapy.
Adult Dose	Apply copious amounts of lotion to dry hair and massage; leave on 8-12 h, rinse, and remove nits with fine-tooth comb (repeat in 7-10 d if lice present)
Pediatric Dose	<2 years: Not recommended >2 years: Administer as in adults
Contraindications	Documented hypersensitivity; contraindicated in neonates and infants because of increased transdermal absorption
Interactions	None reported; however, potential exists for interaction with aminoglycosides and antimyasthenics
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Contains flammable alcohol; do not expose lotion or wet hair to open flame or electric heat, eg, hair dryers (allow hair to dry naturally and uncovered following application); avoid contact with eyes (flush eyes immediately with water if contact)

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Outpatient Care

• It may be beneficial to launder potential fomites (eg, towels, pillowcases, sheets, hats, children's stuffed animals) in hot water, followed by machine drying using the hottest cycle.
• • Temperatures exceeding 131 degrees F (55 degrees C) for more than 5 minutes kill eggs, nymphs, and mature lice.
  • Dry cleaning may be an effective alternative.
• Combs and brushes can be treated by soaking for more than 5 minutes in very hot water (>131 degrees F or 55 degrees C).
• Since adult lice cannot survive for long if they are separated from a host, and since eggs hatch in 6-10 days, carefully sealing potential fomites in plastic bags for 12-14 days can be effective. This technique works well for objects such as stuffed animals that do not tolerate laundering or dry cleaning.
• Vacuuming selected areas of the home, including couches used by patients with infestation, is recommended by some as an adjunctive control measure.
• Chemical insecticide sprays used in the home environment have not been shown to be effective in the control of head lice.

Deterrence/Prevention

• To prevent reinfestation, consider treating contacts of a patient with infestation at the same time as the patient.
• Washing combs, brushes, and other fomites reduces reinfestation.

Complications

• Frequent use of pediculicides may cause persistent itching.
• Secondary bacterial infection may occur

Prognosis

• Treatments are highly effective in killing nymphs and mature lice but less effective in killing eggs.
• Appropriate therapy produces a cure in more than 90% of cases.
• After proper treatment, children may return to school, provided that repeat therapy is performed in 7-10 days.

Patient Education

• Noncompliance is the most common cause of treatment failure. Therefore, time is well-spent providing patients with detailed instructions regarding the application and timing of medications used in treatment.
• • Most patients benefit from an understanding of the life cycle of lice and the limitations of medical therapy (eg, medications are incompletely ovicidal).
  • Compliance with retreatment in 7-10 days may be enhanced if patients understand the need for retreatment to kill newly hatched nymphs.
• Poor hygiene is not a risk factor in acquiring pediculosis capitis.
• For excellent patient education resources, visit eMedicine's Parasites and Worms Center. Also, see eMedicine's patient education articles Lice and Crabs.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Lindane (Kwell) treatment is associated with seizures. Therefore, many authors recommend that it not be used as a first-line therapy.
• Pyrethrin products are contraindicated for patients with allergy to chrysanthemums.

Special Concerns

• Pubic lice have been associated with sexually transmitted diseases. Upon making this diagnosis, screening the patient for common sexually transmitted diseases is prudent.
• Remember that pubic lice in children may be an indication of sexual abuse.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• 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. [Medline].
• Benenson AS, ed. Pediculosis. In: Control of Communicable Diseases in Man: An Official Report of the American Public Health Association. 15th ed. Washington, DC: The Association;1990: 316-318. [Medline].
• 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].
• 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].
• 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].
• 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].
• 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].
• The Medical Letter. Drugs for head lice. Med Lett Drugs Ther. Jan 17 1997;39(992):6-7. [Medline].

Article Last Updated: Jan 4, 2007