Overview

Pediculosis (lice infestation) is a common parasitic infection. Three types of lice that infest humans are head lice (Pediculus humanus capitis), body lice (Pediculus humanus corporis), and pubic lice (Phthirus pubis). The arachnids remain on the host until eradicated.

Head lice usually infest the head and live on the scalp. Adult lice lay eggs (“nits”) that are about 1 mm in diameter and typically found within 4 mm of the scalp. Once hatched, lice must begin feeding within 24 hours or they die. The nymph (newly hatched, immature louse) resembles an adult and matures within 8–9 days. The nymph is active and tends to move about the head, whereas adults are less active. Without treatment, this cycle may repeat every 3 weeks.

Body lice (“cooties”) live, hide, and lay their eggs in clothing, particularly in the seams and folds of underclothes. They periodically attack body areas for blood feedings and can transmit infections such as typhus and trench fever.

Pubic lice, or “crabs” (referring to their crab-like appearance), usually are found in the pubic area but may infest armpits, eyelashes, mustaches, beards, and eyebrows.

Epidemiology

• Approximately 10–12 million people in the United States are affected by pediculosis each year, most of them children ages 3–12 years.
  
• Head lice are the most common cause of lice infestation.
  
  
  
  • Outbreaks of head lice infestation are common in places such as schools and day care centers. Outbreaks usually peak after the opening of schools each year, between August and November.

Etiology

• Infestations of head lice are spread through close personal contact or sharing of personal items such as caps, hairbrushes, and combs. Parents of children with head lice should be reassured that the condition is not the result of poor hygiene.
  
• Infestations of body lice generally occur in individuals who do not shower or change clothing frequently (such as homeless men and women).
  
• Pubic lice generally are transmitted through high-risk sexual contact. They also may be spread by way of toilet seats, shared undergarments, or bedding.

Signs and Symptoms

• The bite of a louse causes an immediate wheal to develop around the bite, with a local papule appearing within 24 hours. Pruritus is common.
  
• In many cases of pediculosis, visual inspection of the affected area will verify the presence or absence of head lice or nits.
  
  
  
  • Adult lice are about the size of a sesame seed. They often are difficult to locate, but nits and nit casings generally can be spotted at the base of hair shafts.
  
  
• Inspections for head lice should focus on the crown of the head, near the ears, and at the base of the neck.
  
  
  
  • The grayish nits blend in well with the hair, but nit casings (from hatched nits) are a lighter color and are located more easily.
    
  • Nits and nit casings may be differentiated from dandruff, dirt, and so on by their firm attachment to the hair shaft.
    
  • The presence of black powdery specks (lice feces) also is evidence of an infestation.
  
  
• The presence of body lice can be determined by identifying adult lice and nits in seams of clothing.

Complications

• Itching and subsequent scratching can result in secondary infection.

Treatment

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