Lice

Definition/diagnostic criteria Lice infestations are caused by small, wingless insects infesting the human scalp (head lice, body lice or pubic lice). Head lice (Pediculus humanus capitis) are most prevalent, especially in children. Diagnosis primarily involves identifying live lice, although seeing nits (lice eggs) close to the scalp can support the diagnosis.

Epidemiology Lice infestations are common, particularly in school-aged children. Head lice affect 1-3% of primary school children in the UK at any given time. They are more prevalent in girls than boys, likely due to longer hair and more head-to-head contact. Body and pubic lice are less common and typically associated with poor hygiene and close physical contact, respectively.

Diagnosis
Clinical features: Head lice present with itching of the scalp, although this may not always be present. Nits are seen attached to hair shafts, and live lice may be visible on close inspection. Body lice infestations present with itching, redness, and sometimes with secondary bacterial infection due to scratching. Pubic lice cause itching in the affected area and may be seen in pubic hair.

Investigations: Diagnosis is clinical, based on the detection of live lice. A fine-toothed ‘detection comb’ is more effective than visual inspection for diagnosing head lice.

No laboratory tests are required unless secondary infection is suspected, in which case skin swabs may be taken for bacterial culture.

Treatment Treatment involves mechanical removal and/or insecticides. Mechanical removal is achieved by wet combing. Insecticides such as malathion or dimeticone can be used if wet combing is not effective or not suitable. These treatments should be repeated as per product instructions to catch any newly hatched lice.

For body and pubic lice, topical insecticides such as permethrin are effective. Washing clothing and bedding at high temperatures is recommended to prevent re-infestation.

In cases of persistent lice, consider incorrect application of treatment, re-infestation, or resistance to insecticides. Alternative treatments or a combination of mechanical and chemical methods may be necessary.

Prognosis With appropriate treatment, the prognosis for lice infestation is excellent. Head lice infestations are not associated with significant morbidity but can cause distress and stigma. Recurrence is common, particularly in children, due to re-infestation from close contacts.