Lice (Pediculosis)

Lice (Pediculosis) is a topic covered in the 5-Minute Pediatric Consult.

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Basics

Description

Infestation of the head, body, or anogenital region by parasitic, wingless insects that feed exclusively on human blood

Epidemiology

  • Head lice
    • Spread by head-to-head contact
    • Most common among children 3 to 12 years old
    • Associated with female gender, crowded living conditions
    • Less common among African Americans
    • Point prevalence estimates range from <1% in some places to >90% in others.
    • In the United States, seasonal peak of prescriptions for treatment are filled in July to September coinciding with the back-to-school period.
  • Body lice
    • Spread by close physical contact with infested persons, clothing, or bedding
    • Associated with poor sanitation, cool climates, homelessness, war, disasters, refugee camps
    • No racial or gender differences
  • Pubic lice
    • Usually sexually transmitted
    • Can also spread through contact with clothing or bedding recently used by infested person
    • Most common among young adults

Incidence

  • Varies widely with location and living conditions
  • Estimated 6 to 12 million cases of head lice per year in the United States among children ages 3 to 11 years

General Prevention

Humans are the only host for all three types of lice. Recurrences are common and may be prevented by examining and treating close contacts, especially bedmates.

  • Head lice
    • Avoid head-to-head contact with infested persons; don’t share brushes, hats, or hair ties.
    • Avoid lying on pillows, furniture, or stuffed toys used by infested persons within last 2 days.
    • Wash clothing and bedding used by infested persons with hot water (≥130°F) and set dryer to highest heat setting. Items may also be dry-cleaned or sealed in a plastic bag for 2 weeks.
    • Treatment of furniture, upholstery, and carpets is not necessary because lice only survive for a short while away from host, making transmission via textiles extremely unlikely.
    • Environmental insecticide is not helpful.
    • Treatment of pets is not necessary.
    • “No-nit” school policies do not control head lice transmission and are not recommended.
  • Body lice
    • Regularly wash clothes.
    • Avoid using clothing or bedding used by infested persons.
  • Pubic lice
    • Avoid close body contact or sharing clothes with infested persons.
    • Not prevented by condom use

Pathophysiology

  • Lice bites are painless.
  • To facilitate the blood meal, lice inject enzymes, anticoagulant, and vasodilators. These provoke host inflammatory response causing pruritus.
  • Bites cause intradermal hemorrhage with infiltrates of eosinophils and lymphocytes.
  • Excoriation can introduce secondary infections.
  • Vector-borne pathogens (body lice only) can cause chronic bacteremia, angiomatosis, or endocarditis.

Etiology

  • Head lice (Pediculus humanus capitis)
    • Adult lice are white to gray, 2- to 4-mm long, have six legs, and no wings. They crawl quickly away from threat or bright light and cannot jump or fly. If removed from host, lice will die within 2 days.
    • Females lay up to eight eggs (also called “nits”) per day over a 2- to 3-week lifespan, attaching nits to base of hair shafts with adhesive.
    • Nymphs hatch from nits in 7 to 12 days, leaving behind empty white nit casings on hair.
    • Emerging nymphs die without a blood meal within a few hours. Nymphs molt 3 times over 9 to 11 days to become nit-laying adults.
    • Typical infestation includes lice in all stages of development.
  • Body lice (Pediculus humanus corporis)
    • Morphology and life cycle are similar to head lice, but adults are slightly larger.
    • Live and lay eggs on clothing and only come to the skin to feed 4 to 5 times per day
    • Able to live longer off host than head lice
    • Nits hatch in 6 to 10 days
  • Pubic lice (Phthirus pubis)
    • Crab-like appearance with larger talus adapted to coarser hair
    • Predilection for pubic hair; may also infest axillary hair, perianal area, eyelashes, beard, and rarely scalp

Commonly Associated Conditions

  • Body lice
    • May act as a vector for epidemic typhus (Rickettsia prowazekii), relapsing fever (Borrelia recurrentis), trench fever (Bartonella quintana), or plague (Yersinia pestis)
  • Pubic lice
    • Commonly occurs with other sexually transmitted infections
    • Although pubic lice on children’s eyelashes usually result from close contact with infested parent, must also consider sexual abuse

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