Pediculus humanus capitis

Background

• Human head louse
• Greyish-white insect
• Eggs (nits) are cemented on hair shaft, and hatch in about 8 days
• Moult three times before becoming sexually mature over 8 to 9 days

Epidemiology

• Transmitted by close contact
  • Fomite transmission is uncommon, but can happen with hair brushes, combs, clothing, headphones, towels, or bedding

Clinical Manifestations

• Often asymptomatic
• Pruritis can occur due to delayed type IV hypersensitivity reaction to louse saliva
  • Initially 2 to 3 weeks to develop, but sooner on repeat infestation

Differential Diagnosis

• White piedra, more common in tropical countries, and surrounds the hair follicle but is much further up on the hair shaft than a nit
• Hair casts from seborrheic dermatitis, which come similar to dandruff but surrounds the follicle, and comes right off unlike a nit

Diagnosis

• Identification of louse in the hair
  • May need a louse comb
  • One louse is enough for diagnosis
  • Found anywhere on the scalp but most commonly nape of the neck and behind the ears
  • Nits are laid at the base of the hair follicle, but then moves out as the hair continues to grow

Management

• Permethrin 1% cream rinse
  • Wash hair and towel dry
  • Saturate hair with permethrin and leave for 10 minutes
  • Repeat at 7 to 10 days
• Alternative treatments
  • Wet coming using olive oil or hair conditioner, then combing with fine-toothed comb every 3 to 4 days
  • Ivermectin
  • Head shaving
  • Suffocation of lice (not effective)
  • Heat treatments (not very effective)
  • Electrocution treatments (not very effective)
    • Includes vacuum devices

Treatment Failure

• Resistance is rare; much more likely to be:
  • Non-adherence to treatment
  • Poor application of pediculocide
  • Inadequate amount of pediculocide
  • Reinfestation
• If treatment failure and was applied properly, can repeat treatment with an alternative agent

Prevention

Infection Prevention and Control

• Treat any infected contacts
• Treat bunkmates empirically
• Wash any clothing and bedding that was used by the infested patient within the past 48 hours