A 12-year-old girl presented to a homeless clinic with her mother for itching on her head. The physical examination revealed multiple nits in her long straight hair (Figure 127-1). A live adult louse was also found crawling on the hairs around her neck (Figure 127-2). The clinician also examined her mother and found a few nits on the hair behind her ears. There were no other members of the family living at the shelter so both were treated with permethrin now and in one week to kill any remaining live nits before they hatch. The clinician alerted the shelter staff of this infestation and other families were found to be infested. The girl was given permission to return to school if she completed her treatment with the permethrin cream rinse. The clinician recommended that clothes, bed clothes, combs and brushes be washed in hot water.

Lice are ectoparasites that live on or near the body.¹ They will die of starvation within 10 days of removal from their human host. Lice have coexisted with humans for at least 10,000 years.² Lice are ubiquitous and remain a major problem throughout the world.³

Pediculosis, crabs (pubic lice).

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  Human lice (pediculosis corporis, pediculosis pubis, and pediculosis capitis) are found in all countries and climates.³

  
  
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  Head lice are most common among school-age children. Each year, approximately 6 to 12 million children, ages 3 to 12 years, are infested.⁴

  
  
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  Head lice infestation is seen across all socioeconomic groups and is not a sign of poor hygiene.⁵

  
  
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  In the US, black children are affected less often as a result of their oval-shaped hair shafts that are difficult for lice to grasp.⁴

  
  
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  Body lice infest the seams of clothing (Figure 127-3) and bed linen. Infestations are associated with poor hygiene and conditions of crowding.

  
  
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  Pubic lice are most common in sexually active adolescents and adults. Young children with pubic lice typically have infestations of the eyelashes. Although infestations in this age group may be an indication of sexual abuse, children generally acquire the crab lice from their parents.⁶

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  Lice are parasites that have six legs with terminal claws that enable them to attach to hair and clothing. There are three types of lice responsible for human infestation. All three kinds of lice must feed daily on human blood and can only survive 1 to 2 days away from the host. The three types of lice are as follows:

  
  
  
  
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    Head lice (Pediculus humanus capitis)—Measure 2 to 4 mm in length (Figures 127-2 and 127-4).

    
    
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    Body lice (Pediculus humanus corporis)—Body lice similarly measure 2 to 4 mm in length (Figure 127-5).

    
    
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    Pubic or crab lice (Phthirus pubis)—Pubic lice are shorter, with a broader body and have an average length of 1 to 2 mm (Figure 127-6).

  
  
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  Female lice have a lifespan of approximately 30 days and can lay approximately 10 eggs (nits) a day.⁴

  
  
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  Nits are firmly attached to the hair shaft or clothing seams by a glue-like substance produced by the louse (Figure 127-7).

  
  
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  Nits are incubated by the host’s body heat.

  
  
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  The incubation period from laying eggs to hatching of the first nymph is 7 to 14 days.

  
  
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  Mature adult lice capable of reproducing appear 2 to 3 weeks later.⁵

  
  
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  Transmission of head lice occurs through direct contact with the hair of infested individuals. The role of fomites (e.g., hats, combs, brushes) in transmission is negligible.⁶ Head lice do not serve as vectors for transmission of disease among humans.

  
  
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  Transmission of body lice occurs through direct human contact or contact with infested material. Unlike head lice, body lice are well-recognized vectors for transmission of the pathogens responsible for epidemic typhus, trench fever, and relapsing fever.⁵

  
  
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  Pubic or crab lice are transmitted primarily through sexual contact. In addition to pubic hair (Figure 127-8), infestations of eyelashes, eyebrows, beard, upper thighs, abdominal, and axillary hairs may also occur.