Head Lice

Definition /diagnostic criteria Head lice (Pediculus humanus capitis) are obligate ectoparasites that live on human hair and feed on human blood. Diagnosis is typically confirmed by the identification of live lice or viable eggs (nits) on the hair or scalp. It is important to distinguish between live and dead or empty egg casings, as the latter does not indicate an active infestation.

Epidemiology Head lice infestation is common, particularly in children aged 4 to 11 years, and is not an indication of poor hygiene. Transmission occurs through direct head-to-head contact, with lice unable to jump or fly. Despite common misconceptions, there is little evidence to suggest that sharing hats or combs plays a significant role in transmission.

Diagnosis
Clinical features: The primary symptom of head lice infestation is itching, although not everyone experiences this.

• Itching results from an allergic reaction to the saliva of lice and may not develop until several weeks into the infestation.
• Nits (eggs) are often visible on the hair shafts, close to the scalp, and are most commonly found behind the ears and at the nape of the neck.
• Live lice are harder to spot and are small, wingless insects that move quickly away from light.

Investigations: The diagnosis is primarily clinical, based on the identification of live lice.

• The gold standard for detection is wet combing, also known as the ‘detection combing’ method. This involves using a special fine-toothed head lice comb on wet and conditioned hair to trap and remove lice.
• Dry combing can also be used but is less effective.

Treatment A stepwise approach to treatment is recommended, starting with mechanical removal methods before considering insecticides.

• Mechanical removal: Wet combing using the detection combing method. This should be done on days 1, 5, 9, and 13 to catch any newly hatched lice. Checking the hair for lice on day 17 should confirm eradication.
• Insecticides: If wet combing is not effective or not suitable, consider using an insecticide treatment. The choice of insecticide should be based on patient preference, cost, and any previous treatments used. The two main types are:
  – Dimeticone 4% lotion, applied twice, seven days apart.
  – Malathion 0.5% aqueous liquid, applied twice, seven days apart.

It’s crucial to follow the instructions regarding application and duration of treatment to avoid resistance and ensure effectiveness. Treat all affected family members simultaneously to prevent re-infestation.

Prognosis With proper treatment, the prognosis for head lice infestation is excellent. However, reinfestation is common, especially in school-aged children. There is no evidence to suggest that head lice have a preference for dirty or clean hair, and their presence is not an indication of poor personal hygiene.