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
  • Point prevalence differs geographically from <1% to >90%.
  • More prevalent in ages 3 to 11 years and females; less prevalent in African Americans
  • Associated with warmer weather and crowded living conditions
• Body lice
  • Spread by close physical contact with infested persons, clothing, or bedding
  • No differences in prevalence by race or gender
  • Associated with poor sanitation, damp, cold weather, homelessness, war, disasters, and refugee camps
• Pubic lice
  • Spread primarily by sexual contact and also by contact with infested clothing or bedding
  • Most prevalent in young adults

ETIOLOGY

• Head lice (Pediculus humanus capitis)
  • Three life stages: egg (also called nit), nymph (immature form), and adult (mature form); typical infestation includes lice in all stages; treatment effect depends on life stage.
  • Adult head lice are white-gray color, 2- to 4-mm long with six legs, and no wings. Adult lice are unable to jump or fly and die without blood meal within 2 days.
  • Adult females lay up to 10 eggs per day over 2 to 3 weeks, attaching the eggs to the base of hair shafts.
  • Eggs hatch in 7 to 12 days; afterward, empty egg casings remain adhered to hair.
  • Nymphs die without blood meal within a few hours; nymphs molt 3 times over 9 to 11 days before becoming adults.
• Body lice (Pediculus humanus corporis)
  • Morphology and life cycle are similar to that of head lice, but adult body lice are slightly larger, lay more eggs, and grow faster.
  • Live and lay eggs on clothing; travel to skin to feed 4 to 5 times per day
• Pubic lice (Pthirus pubis)
  • Life cycle is similar to that of head lice, but adult pubic lice morphology is broader with a larger talus to grip coarser hair.
  • Predilection for pubic hair but may also infest axillary hair, perianal area, eyelashes, beard, and, rarely, scalp

GENERAL PREVENTION

Humans are the only host for all three types of lice. Recurrent infestations are common but may be reduced by assessing close contacts of infested persons, especially bedmates, and periodically assessing asymptomatic children.

• Head lice
  • Avoid head-to-head contact and sharing brushes, hats, and hair accessories with infested persons.
  • Citronella oil applied to the scalp may repel head lice.
  • Use of environmental insecticides is not helpful. Other environmental measures (e.g., treating clothing, bedding, pets) are not necessary.
  • “No-nit” school policies are not recommended because nits (eggs) alone do not indicate active infestation.
• Body lice
  • Regularly wash clothing and bedding.
  • Avoid using clothing or bedding used by infested persons.
• Pubic lice
  • Avoid close body contact or using clothing worn by infested persons.
  • Condom use does not prevent transmission.

PATHOPHYSIOLOGY

• To facilitate the blood meal, lice inject enzymes, anticoagulant, and vasodilators. These provoke a host inflammatory response causing pruritis.
• Bites induce intradermal hemorrhage and subsequent infiltration of eosinophils and lymphocytes.
• Bites are painless, but excoriation can introduce secondary infections.
• Body lice infestations may introduce vector-borne pathogens that can cause chronic bacteremia, angiomatosis, or endocarditis.

COMMONLY ASSOCIATED CONDITIONS

• Head lice
  • Sleep can be disrupted due to intense pruritus.
  • Mental health will suffer if infestation causes social isolation, teasing, or bullying.
  • Academic or work performance can be impaired if days will be lost to school or work due to “no-nit” policies.
  • Pyoderma and lymphadenopathy can result from secondary bacterial infections.
• Body lice
  • May act as a vector for epidemic typhus (Rickettsia prowazekii), relapsing fever (Borrelia recurrentis), trench fever (Bartonella quintana), or plague (Yersinia pestis)
  • May coexist with head lice and pubic lice
• Pubic lice
  • Commonly occurs with sexually transmitted infections
  • Although pubic lice on children’s eyelashes usually result from close, nonsexual contact with an infested parent, clinicians must also consider sexual abuse.