Head lice

• Head lice:

  • Pediculosis capitis
  • Common parasite infestation
  • The head louse (Pediculus humanis capitis) infests the hairs on the scalp and feeds on human blood
  • Typically affects primary school-aged children and their families
• Aetiology:

  • Most commonly spread by direct head-to-head contact, allowing the lice to crawl from one host to another
  • A louse can only survive 1-2 days away from a human host
• Head lice life cycle:

  • Adult lice - inject the scalp with salvia and feed on human blood, causing itching and irritation. Females lay up to 10 eggs daily and live up to 30 days.
  • Louse eggs (ova or nets) - oval and brown, become yellowish once hatched. Laid close to the scalp and attached to hair shafts, taking just over a week to hatch
  • Nymphs (baby lice) - take 7-10 days to mature. Females lay eggs and restart the cycle
  • Untreated, the cycle repeats every 3 weeks
• Risk factors:

  • Age 4-11 years
  • Female sex
  • Sharing beds, clothing, and hairbrushes
  • Greater number of children in the family
  • Overcrowded living conditions
• Typical symptoms:

  • Scalp pruritus
  • Feeling of things moving in the hair
  • Scratching, causing crusting and scale
• Clinical exam:

  • Visible live nymphs or adult lice or eggs
  • May be small red papules under the hairline at the nape of the neck and behind the ears - louse bites
  • Severe cases may cause cervical lymphadenopathy
• Headlice should be treated as soon as they are spotted. Close contacts (including daycare/school) should be informed. Other household members should be checked for headlice and, if infected, treated simultaneously to prevent re-infestation. 
• Topical therapy:

  • Insecticide is recommended - first line dimeticone
  • Other insecticides - malathion, permethrin or ivermectin (ivermectin when others have failed)
  • Kills the louse by coating it with a physical barrier, causing suffocation
  • Should be at least 2 application of insecticide. 2nd application should be 7-10 days after the first
• Wet combing:

  • Systematic combing of wet hair with a fine-tooth comb
  • Most effective way to physically remove head lice
  • Can be used as an adjunct with topical therapy or first-line in patients wishing to avoid insecticides
  • Repeat wet combing in 4 sessions spaced over 2 weeks
  • Should be repeated until no lice are found on consecutive occasions
• Wet combing or dimeticone should be used in pregnant or lactating women.
• Head lice is not usually associated with severe complications. However, along with discomfort, it can cause:

  • Secondary bacterial infection (impetigo)
  • Dermatitis: red scaly, itchy plaques
  • Anxiety and distress
  • Lymphadenopathy