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Pediatrics: General Medicine > Dermatology
Pediculosis (Lice)
Article Last Updated: Jan 4, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Wayne Wolfram, MD, MPH, Clinical Associate Professor, Departments of Pediatrics, Children's Hospital and University of Cincinnati
Wayne Wolfram is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, and Society for Academic Emergency Medicine
Coauthor(s):
Neil W Yoder, DO, Staff Physician, Department of Emergency Medicine, St Vincent Mercy Medical Center
Editors: Kevin P Connelly, DO, Clinical Assistant Professor, Department of Pediatrics, Division of General Pediatrics and Emergency Care, Virginia Commonwealth University; Medical Director, Paws for Health Pet Visitation Program; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; Robert A Schwartz, MD, MPH, Professor and Head of Dermatology, Professor of Medicine, Professor of Pediatrics, Professor of Pathology, Professor of Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School; Merrily P M Poth, MD, Professor, Department of Pediatrics and Neuroscience, Uniformed Services University of the Health Sciences; Russell W Steele, MD, Professor and Vice Chairman, Department of Pediatrics, Head, Division of Infectious Diseases, Louisiana State University Health Sciences Center
Author and Editor Disclosure
Synonyms and related keywords:
pediculosis, lice, louse, nits, nymphs, pediculosis capitis, head lice, pediculosis corporis, body lice, pediculosis pubis, pubic lice, crabs, typhus, sexually transmitted diseases, STDs, child sexual abuse, Anoplura, sucking lice, biting lice, Mallophaga, pruritus
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
Pathophysiology
Lice are ectoparasites who live off of human hosts. Lice feed on human blood after piercing the skin and injecting saliva. The injected saliva often causes pruritus. Lice can survive away from a human host for short periods of time. However, lice die of starvation within 10 days of removal from their human host. A mature female lays 3-6 eggs, also called nits, per day. Nits are white and less than 1 mm long. Nits hatch in 8-10 days, reach maturity in 12-15 days, and live as adults for about 10 days. Different species of lice prefer to feed on certain locations on the body of the host. Types of lice include pediculosis capitis (head lice), pediculosis corporis (body lice), and pediculosis pubis (pubic lice, sometimes called crabs).
Mortality/Morbidity
Body lice can be vectors for disease such as epidemic typhus and relapsing fever. Violation of the integrity of the skin from a bite can lead to bacterial infection, including methicillin-resistant Staphylococcus aureus (MRSA). More commonly, infestation with lice produces social embarrassment and isolation rather than medical disease.
Race
People of all races are affected. Reported incidence in African Americans is relatively less than in other American races.
Sex
Males and females are equally at risk for infestation.
Age
People of all age groups are affected. Head lice infestation is common among young school children in the United States. One study estimates that 12-24 million days of school are lost because of "no-nit" school policies.1
History
- Patients may present after discovering lice or nits indicative of infestation.
- Children may be brought to their pediatrician when concerned parents learn about a case of lice at the child's school or daycare center.
- Pruritus is the most common symptom of infestation.
- Affected children are often asymptomatic.
Physical
Pruritus may lead to secondary excoriations that predispose to secondary skin infection and regional lymph node enlargement. However, these are nonspecific findings. - Pediculosis capitis
- Although head lice are found on any part of the scalp, they are most commonly found in the postauricular and occipital areas.
- Eggs depend on body warmth to incubate; a sticky substance attaches nits to the hair shafts within 3-4 mm of the scalp. Because hair grows approximately 10 mm per month, the distance of nits from the scalp can be used to estimate the duration of infestation.
- Pediculosis corporis
- Bites from body lice can be found in any area of the body.
- Because nits are laid in the host's clothing (especially along inner seams of clothing), nits 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 they prefer the perineum and pubic areas. Occasionally, the infestation may be present in the eyebrows and eyelashes.
Causes
- Pediculosis is usually caused by direct contact with an infested person.
- Fomites such as clothing, headgear, combs, and hairbrushes may play a role in the spread of head lice.
Anxiety Disorder: Generalized Anxiety
Child Abuse & Neglect: Sexual Abuse
Impetigo
Scabies
Other Problems to be Considered
Other bites (eg, scabies, fleas)
Other Tests
- The diagnosis rests on the observation of nits, nymphs, or mature lice. Wetting the hair and using a fine-toothed comb can aid in observation.
- 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, but has a wider body than the head or body louse.
- The use of a magnifying glass and the knowledge of where to look aid the diagnosis.
- Nits are fluorescent under a Wood lamp.
Medical Care
- Patient therapy consists of 2 parts: medications and environmental control measures.
- Medical treatment should include contacts of infested patients, especially sexual partners.
- Medications are less essential than environmental measures in the treatment of body lice. Many infectious disease authorities recommend only environmental measures to treat body lice. Patients with body lice should have infested clothing removed and treated. If medical therapy is prescribed as an adjunct to environmental measures, one of the therapies below may be selected.
- Recently, resistance of lice to the most commonly used medications for treatment of infestation (permethrin and pyrethrin) is increasing. This resistance has been reported in the United States as well as countries in South America and Europe. Studies have noted both genetic mutations and an increase in monooxygenase enzyme activity as causing increased resistance.2, 3, 4, 5 Studies have showed that lice are more susceptible to malathion and treatment is more reliable.6 Malathion has proved to be more ovicidal than permethrin and has a higher lethal effect and decreased amount of reinfestation, if used properly. However, resistance to malathion is now starting to be reported in Great Britain. Using medications as directed is extremely important.
- Other treatment options include the following:
- Occlusive therapy techniques, such as vinegar, mayonnaise, petroleum jelly, olive oil, butter, isopropyl alcohol, and water submersion up to 6 hours, are not reliable methods of treatment.
- Hair removal is one option that aids in blockade of propagation because of the need for the lice to lay their eggs on hair shafts. However, cosmetic results tend to make this option less appealing.
- Proper treatment with medication is advised.
Drug Category: Anthelmintics
Parasite biochemical pathways are different from the human host; thus, toxicity is directed to the parasite, egg, or larva. Mechanism of action varies within the drug class. Antiparasitic actions may include the following:
- Inhibition of microtubules causing irreversible block of glucose uptake
- Tubulin polymerization inhibition
- Depolarizing neuromuscular blockade
- Cholinesterase inhibition
- Increased cell membrane permeability, resulting in intracellular calcium loss
- Vacuolization of the schistosome tegument
- Increased cell membrane permeability to chloride ions via chloride channels alteration
| Drug Name | Permethrin (Elimite, Nix) |
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| Description | DOC recommended by most authorities. Very effective in killing adult lice and nymphs, but not as effective in killing nits (eggs). Neurotoxin that causes paralysis and death in ectoparasites. Available as 5% cream prescription strength (Elimite) and a 1% OTC cream rinse (Nix). Recently, resistance to treatments has been observed. Strict adherence to the treatment regimen is essential. |
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| Adult Dose | Wash hair with a nonmedicated shampoo and towel dry, then apply permethrin as a cream rinse, allow to remain in place for 10 min, then rinse hair thoroughly
Because permethrin does not destroy nits effectively, a second application (using the same technique) is often recommended 7-10 d after initial therapy |
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| Pediatric Dose | <2 months: Not established
>2 months: Administer 1% cream rinse as in adults |
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| Contraindications | Documented hypersensitivity to pyrethroids, pyrethrin, or chrysanthemums |
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| Interactions | None reported |
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| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
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| Precautions | An important adjunct is use of a fine-toothed comb to remove nits; for external use only; may cause rash, burning stinging pain, edema, and tingling in applied region; do not apply to eyes or lashes |
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| Drug Name | Pyrethrins (A200 Pyrinate, Rid Mousse, RID Shampoo, End Lice) |
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| Description | Used as an alternative to permethrin. More likely to require repeated applications. |
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| Adult Dose | Wash hair with a nonmedicated shampoo and towel dry, then apply permethrin as a cream rinse, allow to remain in place for 10 min, then rinse hair thoroughly
Because it may not effectively destroy nits, a second application (using the same technique) is often recommended 7-10 d after initial therapy |
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| Pediatric Dose | Administer as in adults |
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| Contraindications | Documented hypersensitivity to pyrethrum products or ragweed |
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| Interactions | None reported |
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| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
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| Precautions | A second treatment in 7-10 d is necessary to kill newly hatched nymphs; for external use only; use fine-toothed comb to remove nits; may cause rash or irritation to treated area; do not apply to eyes or lashes |
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| Drug Name | Lindane 1% lotion and shampoo |
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| Description | Treatment has been associated with seizures; therefore, it is usually recommended as second-line treatment for patients who do not respond to permethrin or pyrethrin. Neurotoxin that causes seizures and death in parasitic arthropods. |
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| Adult Dose | Apply as a cream rinse after shampooing with a nonmedicated shampoo; allow to remain in place for no more than 4 min, then thoroughly rinse |
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| 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 |
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| Contraindications | Documented hypersensitivity; premature neonates; acutely inflamed skin or raw weeping wounds |
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| Interactions | Caution with drug that lower seizure threshold (eg, antipsychotics, antidepressants, theophylline, cyclosporine, mycophenolate, tacrolimus, imipenem, quinolone antibiotics, chloroquine, pyrimethamine, isoniazide) |
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| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
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| Precautions | A second treatment in 7-10 d is necessary to kill newly hatched nymphs; use with caution in infants and small children or patients with a history of seizures; may cause alopecia, dermatitis, headache, dizziness, paresthesia, or urticaria; for external use only; use fine-toothed comb to remove nits; may cause rash or irritation in treated area; do not apply to eyes or lashes |
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| Drug Name | Mercuric oxide ophthalmic ointment 1% |
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| Description | Use for louse infestation of eyelashes. |
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| Adult Dose | Apply to eyelashes qid for 14 d |
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| Pediatric Dose | Administer as in adults |
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| Contraindications | Documented hypersensitivity |
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| Interactions | None reported |
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| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
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| Precautions | Inspect eyelids for nits and remove them mechanically; for external use only |
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| Drug Name | Malathion 0.5% (Ovide Lotion) |
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| Description | Approved by FDA in 1999 for the treatment of head lice. Irreversible cholinesterase inhibitor hydrolyzed (and therefore detoxified) rapidly by mammals but not by insects. This drug is both oviducal and pediculicidal. Also binds to hair and may provide some residual protection after therapy. |
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| Adult Dose | Apply lotion to dry hair in quantity sufficient to wet hair and scalp, massage and leave on for 8-12 h; do not apply heat (eg, hairdryers, hot curlers); rinse and remove nits with a fine-toothed comb
Repeat treatment in 7-10 d if lice are still present |
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| Pediatric Dose | <2 years: Not established
>2 years: Administer as in adults |
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| Contraindications | Documented hypersensitivity; neonates and infants |
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| Interactions | None reported with external use |
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| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
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| Precautions | The alcohol may irritate excoriated skin; the lotion is flammable; take care to avoid mucosal surfaces, eyes, and heat sources (eg, hair dryers); for external use only; do not apply to eyes or lashes |
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Further Outpatient Care
Treatment of the patient's environment (control measures) include the following:
- Potential fomites such as towels, pillow cases, sheets, hats, and children's stuffed animals may benefit from laundering in hot water and machine drying, using the hottest cycle. Temperature exceeding 131°F (55°C) for more than 5 minutes kills eggs, nymphs, and mature lice.
- Combs and brushes can be treated by soaking for at least 5 minutes in very hot water (>131°F or 55°C).
- Dry cleaning may be an effective alternative.
- Because adult lice cannot survive for long if separated from a host and because 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, such as couches used by infested patients, 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, contacts of an infested patient should be treated and re-treated at the same time as the patient.
Prognosis
- Treatments are highly effective in killing nymphs and mature lice but are less effective in killing eggs. After proper initial treatment, children may return to school if repeat therapy is administered in 7-10 days.
Patient Education
- Patients should be provided with detailed instructions regarding the proper application of medications used in treatment.
- Most patients benefit from an understanding of the life cycle of lice and the limitations of medical therapy (ie, medications are incompletely ovicidal). Compliance with a second treatment in 7-10 days may be enhanced if patients understand the need for the second treatment to kill newly hatched nymphs.
- For excellent patient education resources, visit eMedicine's Parasites and Worms Center. Also, see eMedicine's patient education article Lice and Crabs.
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 ragweed.
Special Concerns
- Pubic lice have been associated with sexually transmitted diseases (STDs). Upon making this diagnosis, screening the patient for common STDs is prudent.
- Remember that pubic lice in children may be an indication of sexual abuse.
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Pediculosis (Lice) excerpt Article Last Updated: Jan 4, 2008
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