• Clinical science

Lice infestation

Summary

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. Affected individuals most commonly present with pruritus; although early stages of infestation and mild cases may be asymptomatic. Detection of lice or nits (louse eggs) on the body or clothes usually confirms the diagnosis. Treatment includes topical pediculicides as well as nonpharmacologic measures (e.g., machine washing and drying contaminated clothing/sheets). Secondary skin infections from scratching may occur in all forms of pediculosis (lice infestation). The body louse acts as a vector for louse-borne diseases, including epidemic typhus, trench fever, and relapsing fever.

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 (affects 1% of school-aged children in North America)
  • Clinical features: : may be asymptomatic initially and in mild cases; scalp/neck pruritus
  • Diagnosis
    • Detection of nymphs and adult lice on the scalp or hair (often visible with the naked eye)
    • Confirmation with microscopy of a hair shaft or Wood's lamp examination (nits fluoresce 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 shampoo, topical ivermectin, benzyl alcohol, and spinosad
    • Clean combs, hair brushes, and hair accessories of lice and nits (i.e., soak in hot water for 5–10 minutes)
    • Machine wash and dry bedding, clothes, etc. (≥ 55°C (≥ 131°F) for 30 minutes.); alternatively, dry clean or store in a sealed plastic bag for 2 weeks.
    • Children with head lice should receive prompt treatment 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 nits alone does not indicate active infestation!

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 (typically at the waist, neck, and axilla)
  • Diagnosis: detection of lice or nits 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)
    • Machine wash and dry bedding, clothes, etc. (≥ 55°C (≥ 131°F) for 30 minutes); alternatively, dry clean or store in a sealed plastic bag for 2 weeks.
  • Complications

References:[1][3]

Pediculosis pubis (pubic lice infestation)

  • Parasite: 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: : usually sexual contact (can also be transmitted via infested towels or bedding)
  • Epidemiology: most common in teenagers and young adults
  • Clinical features
    • Pruritus in the pubic area is common; can also occur in the perianal and axillary region.
    • Maculae ceruleae (pale blue-purple 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 found)
    • Machine wash and dry bedding, clothes, etc. (≥ 55°C (≥ 131°F) for 30 minutes); alternatively, dry clean or store in a sealed plastic bag for 2 weeks.
    • Screen for other STIs and treat sexual partners to prevent reinfection

References:[1][4]

Louse-borne diseases

Trench fever (five-day fever) [5]

Epidemic typhus

References:[6]

Louse-borne relapsing fever

Borrelia recurrentis causes a recurrent (relapsing) fever.