Lice (pediculosis)


Pediculosis is a benign contagious parasitic infection due to 3 species of lice specific to humans: head lice, body lice and pubic lice. Transmission from person to person occurs through direct or indirect contact.
Body lice are potential vectors of relapsing fever (Chapter 7), typhus (Eruptive rickettsioses, Chapter 7) and trench fever.

Clinical features

– Head lice mainly affect children: itching and scratch marks (nape of neck and around the ears), which may become secondarily infected (impetigo) in prolonged infestation; presence of live lice and/or live (shiny, grey) nits attached to the hair shaft within 5 mm of the scalp.
– Body lice mainly affect populations living under poor conditions (refugees, prisoners, the homeless): itching and scratch marks (back, belt line and armpits), often inflamed and infected; presence of lice and nits in the clothing (parasites are not found on the body).
– Pubic lice are considered to be a sexually transmitted infection (STI): itching and scratch marks (pubic and perianal area), but other hairy areas may also be affected (armpits, thighs, eyelashes); lice and nits at the base of the hair shaft, rarely visible.
– Examine contacts; check for associated systemic infection (body lice) or STI (pubic lice).

Treatment

Head lice

Apply to dry hair 1% permethrin lotion (leave on for 10 minutes) or 0.5% malathion lotion (leave on for 12 hours; 8 hours in children 6 months-2 years). Do not reduce or exceed the recommended duration of treatment. Rinse thoroughly. Decontaminate combs, headwear and bedding (wash ≥ 60 °C/30 min, iron or dry in the sun or, if not feasible, seal in a plastic bag for 2 weeks). Treat those contacts with lice and/or live nits, not those with dead nits alone (dull, white, > 1 cm from scalp) as above. It is recommended to repeat the application after 10 days.

Body lice

Mass treatment (outbreakk)

Apply 30 to 60 g (2 to 4 heaped soup spoons) of 0.5% permethrin powder to the inside of the clothes and underclothes in contact with the skin (front and back, neck and waistline, sleeves and socks) in a fully clothed patient, then rub in the powder by hand. Leave for 12 to 24 hours.
Treat other clothing (including headwear) and bedding in a plastic bag with 0.5% permethrin powder. Repeat in 8 to 10 days if the infestation persists.

Individual treatment

Disinfection of clothing and bedding as above or as for head lice.

Pubic lice

Shave and/or apply 1% permethrin lotion to hairy areas (as for head lice). Treat the partner at the same time. Decontaminate clothing and bedding (as for head lice). Repeat the application after 7 days.

Treatment of secondary bacterial infection, if present, should begin 24 to 48 hours before local antiparasitic treatment (see Impetigo); local treatment is applied later when tolerated.