• Clinical science

Lice infestation

Abstract

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 are obligate stationary ectoparasites that feed solely on human blood. Infested patients can be asymptomatic or most commonly suffer from pruritus. Detection of lice or nits on the body or clothes usually confirms the diagnosis. Treatment of lice infestations include topical pediculicides as well as non-pharmacologic measures (e.g., hot washing of contaminated clothing and sheets).

Pediculosis capitis (head lice infestation)

  • Parasite: Pediculus humanus capitis (∼ 3 mm in length)
  • Transmission: Direct head-to-head contact or sharing hair accessories, bedding or clothing
  • Epidemiology: Most common in children (infects 1% of school-aged children in North America)
  • Clinical features: : asymptomatic; scalp/neck pruritus
  • Diagnosis
    • Detection of nymphs and adult lice in head hair (often visible with the naked eye)
    • Confirmation with microscopy of a hair shaft or Wood's lamp examination (nits flouresce and appear pale blue)
  • Treatment
    • 10 minute topical application of pediculicides followed by mechanical removal with a fine toothed comb (repeat application after 10 days)
      • First-line: 1% permethrin shampoo or pyrethrin
      • Alternative therapies (i.e., in permethrin resistant areas): malathion, benzyl alcohol, spinosad, and topical ivermectin
    • Clear combs, hair accessories, bedding, and clothing of lice and nits (e.g., hot wash)
    • Children with head lice should initiate treatment promptly but can continue attending school.
    • People in close contact with affected individuals should be screened for infestation
  • Complications: Secondary skin infections from scratching and skin break-down

The presence of louse eggs (nits) alone does not indicate active infection!

References:[1][2]

Pediculosis corporis (body lice infestation)

  • Parasite: Pediculus humanus corporis (∼ 3–5 mm in length)
  • Transmission: Direct head-to-head contact or sharing hair accessories, bedding or clothing
  • Epidemiology: : most common in people living in crowded, unsanitary living conditions (e.g., homeless)
  • Clinical features: pruritus; is the chief complaint; puncta from fresh bites; , linear excoriations; , and postinflammatory hyperpigmentation
  • Diagnosis: detection of lice or nits (louse eggs) in clothing; (especially at the seams) with the naked eye, on microscopy, or Wood's lamp examination.
  • Treatment
    • Warm bathing and changing into new clothes
    • Topical pediculicides when nits are detected on body hair (e.g., permethrin)
    • Clean clothes and bedding; (i.e., washing/steaming and heating in a dryer ≥ 55°C (≥ 131°F) for 30 minutes.) or dry cleaning
  • Complications

References:[1][3]

Pediculosis pubis (pubic lice infestation)

  • Parasite: Pthirus pubis ; (also known as the crab louse; often referred to simply as “crabs ); ∼ 1.5 mm in length
  • Transmission: : usually sexual contact (can also be transmitted via infested towels or bedding)
  • Epidemiology: : most common in teenagers and young adults
  • Clinical features
    • Pruritus in pubic area is common (can also occur in axillary region)
    • Maculae ceruleae (pale bluish macules ) in patients with chronic infection
  • Diagnosis: identification of louse or nits in pubic hair; with the naked eye; , during microscopy; , or Wood's lamp examination
  • Treatment
    • 10 minute topical application of pediculicides (e.g., 1% permethrin cream or pyrethrin); reevaluate after 9–10 days, and repeat treatment if lice are seen)
    • Clean infested bedding and clothing (e.g., washing/steaming and drying)
    • Screen for other STIs and treat sexual partners to prevent reinfection

References:[1][4]

Pediculosis ciliaris

  • Parasite: Pthirus pubis (same as in pediculosis pubis)
  • Transmission: direct contact with infested individuals, towels, or bedding
  • Epidemiology: most common in teenagers and young adults (may occur in children in close contact with infested adults)
  • Clinical features
    • Eye pruritis or irritation (usually bilateral)
    • Crusted eyelashes
    • Features of conjuctivitis
  • Diagnosis: detection of lice or nits close to eyelash base (may also be seen in the eyebrows or hairline)
  • Treatment
    • Mechanical removal of lice and nits after applying petroleum jelly to eyelids
    • Treat associated conjunctivitis
    • Local pediculicide treatment for persistant cases if above therapy fails

References:[1][4]

last updated 04/10/2018
{{uncollapseSections(['BAYzN7', 'cvXa_-', 'WvXP_-', '1vX2_-', 'NLc-B10'])}}