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Lice (Pediculosis)

Essentials

  • Head lice often spread through hats and caps or from person to person in close contact.
  • Pubic lice are most easily transmitted by sexual contact.
  • If head lice infestation is detected in several close contacts in a day-care centre or a school, for example, the spread of lice should be assessed in the whole community.

Aetiology

  • Lice are ectoparasites living externally on humans and transmitted through clothes or skin contact.
  • They live attached to their host or to clothes and attach their eggs (nits) to hair. Lice feed on blood they suck from the skin, and their bites cause itching and skin symptoms.
  • Humans can be infested by three species of lice. The clinical manifestations vary mainly because the species specialize in different living environments (see below).
  • Head lice may occur as epidemics in day-care centres or schools, for example.
  • In countries with warm climates, body lice may spread infectious diseases, such as spotted fevers (rickettsioses Bacterial Diseases in Warm Climates).

Symptoms and diagnosis

Head lice (pediculosis capitis)

  • Head lice cause itching and red papules on the scalp and neck. Secondary bacterial skin infections (impetigo, folliculitis) often develop. Secondary eczema and enlarged lymph nodes may occur in the neck area.
  • Diagnosis is based on finding live lice (about 3 mm in size, transparent or grey insects with no wings) or nits 1 on the scalp.
  • Aids such as a magnifying glass or a dermatoscope may often help in finding lice or nits. Nits can best be found deep in the hair on the temples or the back of the head, close to the skin surface. Ordinary dandruff can easily be detached by scraping with a spatula, whereas nits stick to hair.

Body lice (pediculosis corporis)

  • Body lice live in clothes, trouser legs or socks, for example, causing itchy red papules on the trunk and limbs.
  • They mainly occur in patients living in poor hygienic conditions (such as homeless or socially excluded people, people with drug addiction).
  • There are purplish spots (bite sites) predominantly on the trunk and armpits, and often secondary eczema and skin areas broken by scratching.
  • Lice can usually be found in seams of clothes, underneath collars, in cuffs or in socks. It is important also to check garments such as coats, headgear and underwear.

Pubic lice (pthiriasis or pediculosis pubis)

  • The typical clinical picture consists of red papules and skin broken by scratching in the genital area.
  • In areas with thin skin (armpits, trunk, lower abdomen), there may also be purplish macules ("maculae coerulae") due to bites.
  • Nits are most commonly found in pubic hair but they may be found in other skin areas as well (picture 1).
  • Pubic lice may be found in eye lashes, for example.
  • Pubic lice are usually transmitted in close skin contact, such as sexual contact.
  • The diagnosis is based on finding nits or pubic lice. Nits are tightly attached to hair, in contrast with the "hair cast" phenomenon, where a ring of dandruff glides along the hair.
    • Screening for sexually transmitted diseases (such as urine testing for chlamydia and gonorrhoea as well as serum HIV antigen and antibodies) may be indicated in some patients.

Differential diagnosis

Treatment

  • Topical lice treatment products (such as solutions or shampoos) based on either mechanical (e.g. silicone or mineral oils), chemical (e.g. dimethicone) or pharmacological (e.g. permethrin) effects are used to treat head and pubic lice.
  • Treatment with many products is recommended to be repeated after 7-10 days.
  • Nits should be removed with a louse comb, and all close contacts should be checked and treated, as necessary.
  • One of the alternatives is 1% permethrin shampoo (for children over 6 months and adults).
  • In cases that are severe or resistant to treatment, repeated topical treatment (every 7-10 days, for example) should be used, topical treatments should be varied (using products based on various mechanisms, for example), and treatment of close contacts should be ensured.
  • Oral ivermectin (prescription medicine) has also been used for head lice resistant to treatment Oral Ivermectin for Head Lice. Single doses of 200 µg/kg are given twice 7 days apart.
  • In day-care centres and schools, the head louse situation in the whole community should be investigated to avoid epidemics, and close contacts should be actively treated.
  • Children can return to day care or school after starting the first treatment. It is often advisable to inform other contacts, the day-care centre or the school about louse infestation.
  • For repeated infestation, preventive anti-louse treatment at certain intervals has also been used.
  • Changing clothes and facilitating appropriate hygienic measures (washing, washing clothes, etc.) in future is sufficient for the treatment of body lice. Secondary eczema can be treated with a course of a topical glucocorticoid ointment (such as a moderately potent or potent glucocorticoid in a course of 2-3 weeks).

    References

    • Leung AKC, Lam JM, Leong KF, et al. Paediatrics: how to manage pediculosis capitis. Drugs Context 2022;11(): [PubMed]
    • Mohammadi J, Azizi K, Alipour H, et al. Frequency of pyrethroid resistance in human head louse treatment: systematic review and meta-analysis. Parasite 2021;28():86 [PubMed]
    • Mumcuoglu KY, Pollack RJ, Reed DL, et al. International recommendations for an effective control of head louse infestations. Int J Dermatol 2021;60(3):272-280 [PubMed]
    • Coates SJ, Thomas C, Chosidow O, et al. Ectoparasites: Pediculosis and tungiasis. J Am Acad Dermatol 2020;82(3):551-569 [PubMed]
    • Young C, Argáez C. Ivermectin for Parasitic Skin Infections of Lice: A Review of Comparative Clinical Effectiveness, Cost-Effectiveness, and Guidelines [Internet]. Ottawa (ON): Canadian Agency for Drugs and Technologies in Health; 2019 May 14. [PubMed]
    • Salavastru CM, Chosidow O, Janier M, et al. European guideline for the management of pediculosis pubis. J Eur Acad Dermatol Venereol 2017;31(9):1425-1428 [PubMed]