Lice (Pediculosis)
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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Citation
Cabana, Michael D., editor. "Lice (Pediculosis)." 5-Minute Pediatric Consult, 8th ed., Wolters Kluwer, 2019. Pediatrics Central, peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617785/all/Lice__Pediculosis_.
Lice (Pediculosis). In: Cabana MDM, ed. 5-Minute Pediatric Consult. Wolters Kluwer; 2019. https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617785/all/Lice__Pediculosis_. Accessed November 5, 2024.
Lice (Pediculosis). (2019). In Cabana, M. D. (Ed.), 5-Minute Pediatric Consult (8th ed.). Wolters Kluwer. https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617785/all/Lice__Pediculosis_
Lice (Pediculosis) [Internet]. In: Cabana MDM, editors. 5-Minute Pediatric Consult. Wolters Kluwer; 2019. [cited 2024 November 05]. Available from: https://peds.unboundmedicine.com/pedscentral/view/5-Minute-Pediatric-Consult/617785/all/Lice__Pediculosis_.
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