Lice infestation

There are three species of lice that affect humans: Pediculus humanus capitis (head louse), Pediculus humanus corporis (body louse), and Pthirus pubis (pubic or crab louse). All three species are obligate, stationary ectoparasites that feed solely on human blood. Affected individuals most commonly present with pruritus, although early stages of infestation and mild cases may be asymptomatic. Diagnosis is confirmed if at least one viable louse is detected on the head (head lice infestation), or if nits and/or lice are detected on clothing (body lice infestation), pubic area (pubic lice infestation), or eyelashes (eyelash lice infestation). Management of lice infestation varies based on location of infestation and includes pharmacotherapy (for head and pubic infestation), good personal hygiene practices (for body infestation), and nonpharmacological measures such as manual lice removal (for eyelash lice infestation and as an adjunctive measure in other infestations). All patients should be educated on methods to prevent lice transmission and reinfection. Complications of lice infestation include secondary skin infections from scratching.

The body louse acts as a vector for louse-borne diseases. For more information, see “Louse- and flea-borne diseases.”

• Epidemiology: most common in children (affects 1–2% of children in the United States) ^[1][2]
• Parasite: Pediculus humanus capitis (∼ 3 mm in length) ^[1]
• Transmission ^[1]
  • Direct head-to-head contact
  • Sharing hair accessories, bedding, or clothing
• Clinical features ^[2]
  • Can be asymptomatic
  • Visible nymphs, adult lice, and/or nits on the scalp or hair
  • Scalp/neck pruritus and excoriations: can take 4–6 weeks to develop ^[3]
• Management ^[1][2][3]
  • Diagnosis is clinical.
  • Initiate pharmacological treatment for lice infestation. ^[2]
  • Consider nonpharmacological measures as adjunctive or alternative treatments.
    • Lice removal with a fine-tooth comb
    • Occlusive agents (e.g., olive oil and petroleum jelly) ^[1][2]
  • See also “Management of lice infestation.”
• Complications: bacterial superinfection

Identification of ≥ 1 viable louse is necessary for diagnostic confirmation of head lice; detection of nits alone is insufficient. ^[1][3]

Individuals with head lice do not need to be excluded from school. ^[2]

• Epidemiology: most common in people living in crowded, unsanitary living conditions ^[2]
• Parasite: Pediculus humanus corporis (∼ 2–4 mm in length) ^[2]
• Transmission ^[2]
  • Direct contact with infested skin
  • Sharing bedding or clothing
• Clinical features ^[2]
  • Pruritus
  • Erythematous macules and papules with excoriations
  • Postinflammatory hyperpigmentation (typically at the waist, axilla, and neck)
• Management ^[2][3]
  • Diagnosis is clinical.
  • Advise the patient on appropriate personal hygiene measures, e.g.:
    • Regular bathing
    • Using clean clothing and bedding
  • For patients with substantial body hair, consider pharmacological treatment for lice infestation.
  • Fumigation may be necessary if there is potential for transmission of louse-borne disease.
  • See also “Management of lice infestation.”
• Complications
  • Secondary skin infections
  • Possible transmission of one of the following:
    • Rickettsia prowazekii (epidemic typhus)
    • Borrelia recurrentis (relapsing fever)
    • Bartonella quintana (trench fever)

Body lice are most often found in clothing seams rather than on the skin. ^[2]

• Epidemiology: most common in teenagers and young adults ^[2]
• Parasite ; ^[2]
  • Pthirus pubis
  • Also known as the crab louse; often referred to as “crabs” because of its crab-like appearance
  • ∼ 1.5 mm in length
• Transmission ^[2]
  • Usually sexual contact
  • Can also be transmitted via infested towels or bedding
• Clinical features ^[2][4]
  • Pruritus and excoriations in the pubic area (most common) and/or other areas with coarse hair (e.g., axilla, perianal region)
  • Visible lice and/or nits in affected areas
  • Maculae ceruleae (blue-gray macules ) in patients with significant infestation
• Management ^[2][3][4]
  • Diagnosis is clinical; examine all areas of the body with coarse hair (including eyelashes) for additional lice.
  • Lice and nits can be removed with fingernails, a fine-tooth comb, and/or by shaving hair.
  • Initiate pharmacological treatment for lice infestation.
  • Screen for other STIs.
  • Treat all sexual partners from the last month.
  • See also “Management of lice infestation.”

• Parasite: Pthirus pubis (same as in pediculosis pubis) ^[2]
• Clinical features ^[2][4][5]
  • Eye pruritus and/or irritation (usually bilateral)
  • Crusted eyelashes
  • Features of conjunctivitis
  • Visible lice and/or nits at the eyelash base, eyebrows, and/or hairline
• Management ^[2][4]
  • Management is the same as for pubic lice with the following exceptions:
    • Pharmacological treatment for lice infestation is not recommended.
    • Use ophthalmic occlusive agents (e.g., petroleum jelly) at the eyelid margin. ^[4]
  • See also “Management of lice infestation.”

Eyelash lice in children may be a sign of sexual abuse. ^[2]

Diagnostics ^[2][3]

• Examine the area of concern (e.g., scalp, hair, pubic hair, clothing seams, eyelash base) for nits, nymphs, and/or adult lice with any of the following:
  • The naked eye
  • Handheld magnifying glass
  • Wood lamp ^[6]
  • Dermatoscope
  • Microscope
• Diagnosis is confirmed if the following are visualized: ^[2]
  • Head lice infestation: ≥ 1 viable louse
  • Body lice, pubic lice, and eyelash lice infestations: nits and/or lice

Treatment ^[2][3]

• Tailor treatment based on the location of infestation.
• Advise all patients on measures to prevent lice transmission and reinfection.
• See specific sections for details.

Pharmacological treatment for lice infestation ^[2][3]

See “Overview of ectoparasiticides” for additional drug information.

First-line

• Permethrin 1% OR pyrethrins with piperonyl butoxide ^[2][3]
• A second application is recommended after 7–10 days in:
  • All patients with head lice infestation
  • Patients with pubic lice infestation and persistent symptoms ^[4]

Alternatives

The following agents are alternative options in case of known local resistance to pyrethroids or treatment failure with first-line agents. ^[2][4]

• Head lice: Use one of the following agents.
  • Topical ivermectin
  • Spinosad
  • Malathion (if ≥ 6 years of age) ^[2]
  • Oral ivermectin (off-label)
• Pubic lice: malathion (off-label) OR oral ivermectin (off-label) ^[4]

Spinosad, malathion, and topical ivermectin are ovicidal and are typically effective after only one treatment. Permethrin, pyrethrins, and oral ivermectin usually require repeat treatment. ^[3]

Prevention of lice transmission and reinfection ^[1]

• Clean potentially contaminated personal items.
  • Machine wash and dry clothing, bedding, and towels ≥ 54°C (≥ 130°F) for > 5 minutes. ^[1][2][3]
  • Soak combs, hairbrushes, and hair accessories of patients with head lice in hot water ≥ 54°C (≥ 130°F) for 5–10 minutes.
• Examine close contacts for lice infestation and treat if indicated.

Chemical environmental sprays are not routinely recommended for lice management and should only be used if there is potential for transmission of louse-borne disease from body lice. ^[2]