eMedicine Specialties > Emergency Medicine > Infectious Diseases

Pediculosis

Nelly Rubeiz, MD, Consulting Staff, Department of Dermatology, American University of Beirut Medical Center; Associate Professor, Department of Dermatology, American University of Beirut, Lebanon
Abdul-Ghani Kibbi, MD, Chairman and Professor, Department of Dermatology, American University of Beirut Medical Center, Lebanon

Updated: May 5, 2009

Introduction

Background

Infestation with lice is referred to as pediculosis. Lice are ectoparasites that live on the body. The 3 types of lice that parasitize humans are Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Pthirus pubis (pubic louse).

Pthirus pubis (pubic or "crab" louse).

Pathophysiology

Lice have claws on their legs that are adapted for feeding and clinging to hair or clothing. Head and body lice are similarly shaped, but the head louse is smaller. The pubic or crab louse is quite distinct in appearance; it has pincerlike claws resembling those of sea crabs. Lice are blood-sucking insects. They feed on human blood several times daily. They stay close to the skin for moisture, food, and warmth. They move freely and quickly, which explains their ease of transmission. A fertilized female louse lays about 10 eggs a day for up to a month until it dies.

The eggs (nits) are attached to the hair shaft, close to the skin surface, where the temperature is optimal for incubation. The eggs hatch in about 6-10 days. Nits are cemented to the hair shaft with chitin and are very difficult to remove. Nits can survive for up to 10 days away from the human host.

Pubic lice may be found on the short hairs of the body, areolar hair, axillary hair, beard, scalp margins, eyebrows, and eyelashes, in addition to pubic hair.

Body lice and their eggs are predominantly found on clothing and should be looked for in the seams of clothes.

Frequency

United States

Pediculosis affects 6-12 million people annually. P capitis is common among school children. Head lice are very rare among African Americans; this may be due to the twisted nature of the hair shaft and the use of hair pomades. Infestation with P pubis is a sexually transmitted disease (STD).

International

Pediculosis has a worldwide distribution and is endemic both in developing and developed countries. For example, P capitis was found in 9.6% of adolescent schoolboys in Saudi Arabia.¹ In Mali, the prevalence of head lice in children was 4.7%.² Among attendees of a STD clinic in South Australia, pubic lice were found in 1.7% of men and 1.1% of women.³ P corporis is now uncommon in developed countries except in the homeless.⁴

Sex

Pediculosis is more common in females than in males.

Age

Pediculosis can affect any age group.

• P capitis is most frequent in children, especially young and adolescent females. The peak incidence is from age 5-11 years. Direct head-to-head contact is the most common mode of transmission.
• P pubis is most common in sexually active adults.

Clinical

History

• Itching is the most common symptom of the infestation.
• Scratching may cause inflammation and a secondary bacterial infection.

Physical

• P capitis
  • Head lice and nits are found most often on the occiput, posterior neck, and behind the ears.
  • Excoriations on the scalp, posterior neck, and upper back; bite reactions; secondary bacterial infection; and cervical lymphadenopathy are common manifestations.
  • Eyelashes may be involved.
  • Conjunctivitis may be seen.
• P corporis
  • Adult lice and nits are found in clothing seams.
  • Uninfected bites present as erythematous papules, 2-4 mm in diameter, with an erythematous base.
• P pubis
  • Pubic hair is the most common site. The crab louse is found firmly attached to the base of the pubic hair. Nits may also be found.
  • Pubic lice may spread to hair around the anus, abdomen, axillae, chest, and eyelashes.
  • Bluish grey macules, or maculae cerulea, may be seen on the abdomen or thighs and are secondary to the bites of the crab louse.

Causes

• Risk factors
  • Overcrowding
  • Poor hygiene
  • Debilitated and malnourished individuals
  • Sexual promiscuity

Differential Diagnoses

Abortion, Inevitable

Other Problems to Be Considered

Dandruff
Hair casts
Piedra

Workup

Laboratory Studies

• Infestation with P pubis is an STD, and 30% of these patients have a second venereal disease. Screening for other STDs is appropriate, including human immunodeficiency virus (HIV), syphilis, gonorrhea, chlamydia, genital herpes, and trichomoniasis.

Other Tests

• For the diagnosis of P capitis, the use of a louse comb is more efficient than direct visual examination of the scalp. Nits that are within 6 mm from the scalp are usually viable and are opalescent, whereas eggs that have hatched are white. Examine nits and lice under the microscope.
• Slit-lamp examination may reveal pubic lice on eyelashes and eyebrows.
• Live nits are fluorescent white when illuminated with a Wood lamp; empty nits are fluorescent gray.

Treatment

Emergency Department Care

• Nits are best removed with a very fine comb.
• Soaking the hair in a solution of equal parts water and white vinegar and then wrapping the wet scalp in a towel for at least 15 minutes may facilitate removal.
• Treat all family members.
• Discard infested clothing or wash in very hot water.
• Evaluate for other STDs.

Medication

The goal of therapy is to eliminate lice and eggs.

Linen, clothing, and other materials may be treated with hot water washing.

Eyelash infestation can be treated effectively with petrolatum ointment (eg, Vaseline).

Pediculicides

Chemical pediculicides are the mainstay of therapy. Treatment should be repeated in 7-10 days (the time needed for the eggs to hatch) because nits are less effectively killed than adults.

All contacts should be treated simultaneously.

Resistance to pediculicides has increased over recent years. Therapeutic agents can be rotated to slow the emergence of resistance. Benzyl alcohol lotion is a new pediculicide that needs to be applied twice, but it might be an easier and safer alternative to lindane and malathion. With all treatments used to eliminate live lice, careful combing and removal of all nits from the hair as well as cleaning of other articles (ie, hair accessories, towels, bedding, clothing) are essential steps to prevent reinfestation.
 
The safety and effectiveness of benzyl alcohol lotion 5% was demonstrated in 2 multicenter, randomized, double-blind studies of 628 people, 6 months of age and older, with active head lice infestation. Individuals received two, 10-minute treatments of either benzyl alcohol lotion or topical placebo, 1 week apart. In these 2 studies, the drug was effective in eradicating lice in 76.2% and 75% of subjects compared with placebo 4.8% and 26.2%, respectively.⁵

Benzyl alcohol lotion

Benzyl alcohol inhibits lice from closing their respiratory spiracles, allowing the lotion to obstruct the spiracles, which ultimately results in asphyxiation. Does not elicit ovicidal activity. Contains 5% benzyl alcohol.

Dosing

Adult

Apply lotion to dry hair, using enough to completely saturate scalp and hair; rinse off with water after 10 min; repeat treatment in 1 wk

Pediatric

<6 months: Do not use
>6 months: Apply as in adults

Interactions

None reported

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

May cause irritation to skin, scalp, and eyes (avoid eye exposure and flush immediately with water if contact occurs); application site anesthesia and hypoesthesia may occur; serious adverse events (eg, respiratory distress, seizure, coma) and death with benzyl alcohol have been well documented in premature infants; IV administration of products containing benzyl alcohol has been associated with neonatal gasping syndrome consisting of severe metabolic acidosis, gasping respirations, progressive hypotension, seizures, CNS depression, intraventricular hemorrhage, and death in preterm, low birth weight infants; neonates (ie, <1 mo or preterm infants with a corrected age <44 wk) could be at risk for gasping syndrome if treated

Permethrin 5% (Elimite) or 1% (Nix) lotion

DOC, especially for infants >2 mo and small children. More effective than crotamiton in treating symptoms and reducing chances of secondary bacterial infection.
Even after successful treatment, postscabietic nodules and pruritus may persist for mo.

Dosing

Adult

Apply topically to affected area; leave 5-10 min, then rinse

Pediatric

Administer as in adults

Interactions

None reported

Contraindications

Documented hypersensitivity

Precautions

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

Precautions

May exacerbate redness, swelling, and itching, at least temporarily

Lindane 1% shampoo (Kwell)

Stimulates nervous system of parasite, causing seizures and death. Second-line treatment if other agents fail or are not tolerated. Not very safe in children due to transcutaneous absorption leading to neurotoxicity. Overall, permethrin is a safer choice.

Dosing

Adult

Shampoo: Apply to dry head or pubic hair and surrounding areas; allow to set for 4 min, then lather for 4 min and rinse; repeat in 7 d prn

Pediatric

Administer as in adults

Interactions

Oil-based hairdressings may increase toxicity of lindane

Contraindications

Documented hypersensitivity; neonates; acutely swollen skin or Norwegian scabies

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Caution if history of seizures; do not apply to eyes, face, or mucous membranes; penetrates human skin and may cause CNS toxicity in young children, seizures have occurred after inappropriate use or ingestion

Pyrethrin/Piperonyl butoxide shampoo (RID Mousse, RID Shampoo, A-200)

Treatment of P humanus infestations. Stimulates nervous system, causing seizures and death of parasite.

Dosing

Adult

Apply shampoo to dry hair and allow to set for 10 min before rinsing; repeat in 1 wk prn

Pediatric

Administer as in adults

Interactions

None reported

Contraindications

Documented hypersensitivity to product or Compositae plants

Precautions

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

Precautions

Do not apply to eyes, face, or mucous membranes

Malathion (Ovide)

Approved by 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. Available as 0.5% and 1% aqueous-based lotions.

Dosing

Adult

Apply lotion to dry hair; leave on 8-12 h, rinse; repeat in 7 d prn

Pediatric

<2 years: Not recommended
>2 years: Administer as in adults

Interactions

None reported; however, potential for interaction with aminoglycosides and antimyasthenics

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

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)

Ivermectin (Stromectol)

Binds selectively with glutamate-gated chloride ion channels in invertebrate nerve and muscle cells, causing cell death. Half-life is 16 h; metabolized in liver. DOC for onchocerciasis and strongyloidiasis. Recently shown to be effective against pediculosis but not yet approved by FDA. Not effective against nits.

Dosing

Adult

150-200 mcg/kg/d PO as single dose; alternatively, 12 mg PO as single dose; may repeat in 1 wk prn

Pediatric

<5 years: Not established and not recommended
>5 years: 0.2 mg/kg PO as single dose; alternatively, administer as in adults

Interactions

May interact with other ligand-gated chloride channels, such as those gated by GABA

Contraindications

Documented hypersensitivity

Precautions

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

Precautions

Treat mothers who intend to breastfeed only when risk of delayed treatment outweighs possible risks to the newborn caused by ivermectin excretion in milk
Repeat courses of therapy may be required in immunocompromised patients
May cause nausea, vomiting, and mild CNS depression; may cause drowsiness

Follow-up

Further Outpatient Care

• Shaving of the scalp or body hair eradicates lice; however, this is not cosmetically acceptable for most patients.
• Wet combing or application of diluted vinegar or commercial preparations of 8% formic acid may help in the removal of nits or at least make the combing easier. Plastic or the sturdier metal nit combs may be used.
• Multiple lice suffocation agents have been advocated, but most have not been scientifically evaluated. These include Vaseline; petroleum jelly; oils; mayonnaise; and a dry-on, suffocation-based pediculicide lotion (DSP lotion).
• Treatment of the patient's environment is important.
  • Fomites (clothes, towels, beddings, hats, children's stuffed animals) should be washed in hot water, machine-dried, ironed, or dry cleaned. Temperature exceeding 131°F (55°C) for more than 5 minutes kills eggs, nymphs, and mature lice.
  • Combs are hair brushes should be discarded, soaked in very hot water (>131°F or 55°C), or treated with pediculicides.

Deterrence/Prevention

• All household members should be examined and treated at the same time if infested.
• Safe sex practices may decrease the risk of STDs.

Complications

• Persistent pruritus
• Secondary bacterial infection

Prognosis

• Pediculosis has more than a 90% cure rate with appropriate treatment.
• Treatment failures are the result of improper application of pediculicides, noncompliance, reinfestation, or drug resistance.

Patient Education

• For excellent patient education resources, visit eMedicine's Parasites and Worms Center. Also, see eMedicine's patient education article Lice.

Miscellaneous

Medicolegal Pitfalls

• Lindane (Kwell) should be properly used. Seizure may result from abnormal absorption and gross overuse of the product.

Special Concerns

• Pubic lice in children may be an indication of sexual abuse.

Multimedia

Media file 1: Pthirus pubis (pubic or "crab" louse).

References

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Keywords

pediculosis, lice, lice infestation, Pediculus humanus capitis, head louse, head lice, Pediculus humanus corporis, body louse, body lice, Pthirus pubis, pubic louse, pubic lice, lice eggs, nits, typhus, trench fever, relapsing fever, cervical lymphadenopathy, conjunctivitis, human immunodeficiency virus, HIV, syphilis, gonorrhea, chlamydia, genital herpes, trichomonas

Contributor Information and Disclosures

Author

Nelly Rubeiz, MD, Consulting Staff, Department of Dermatology, American University of Beirut Medical Center; Associate Professor, Department of Dermatology, American University of Beirut, Lebanon
Nelly Rubeiz, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Coauthor(s)

Abdul-Ghani Kibbi, MD, Chairman and Professor, Department of Dermatology, American University of Beirut Medical Center, Lebanon
Disclosure: none None None

Medical Editor

David A Peak, MD, Assistant Residency Director of Harvard Affiliated Emergency Medicine Residency, Attending Physician, Massachusetts General Hospital; Consulting Staff, Department of Hyperbaric Medicine, Massachusetts Eye and Ear Infirmary
David A Peak, MD is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, Society for Academic Emergency Medicine, and Undersea and Hyperbaric Medical Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Jeter (Jay) Pritchard Taylor III, MD, Compliance Officer, Attending Physician, Emergency Medicine Residency, Department of Emergency Medicine, Palmetto Health Richland, University of South Carolina; Medical Director, Department of Emergency Medicine, Palmetto Health Baptist
Jeter (Jay) Pritchard Taylor III, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Pamela L Dyne, MD, Professor of Clinical Medicine/Emergency Medicine, David Geffen School of Medicine at UCLA; Attending Physician, Department of Emergency Medicine, Olive View-UCLA Medical Center
Pamela L Dyne, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

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