Lice
(Head Lice · Pediculosis)
In this condition factsheet:
The Facts on Lice
Lice are tiny parasitic insects that can take up residence in a number of different places on our body. They are not a serious medical problem, but they can be annoying and can easily spread and infect others. Lice have been around for centuries. They were widespread in Europe up until the last century, and anthropologists report signs of these annoying intruders among Egyptian mummies and during the period of the ancient Greeks.
Life for a louse begins as a nit (egg). Nits are commonly found glued to the base of the hair shaft, frequently behind the ears or on the nape of the neck. It takes about 5 to 10 days for nits to hatch and for the light-coloured nymphs to begin feeding immediately. It takes about 7 or more days for the nymphs to mature.
Head lice (Pediculus humanus capitis) are found in the hair on the head. They most commonly infect pre-school and elementary school children, but since they spread easily, they can infect anyone. Head lice can infest clothing and other items that come in contact with the head (e.g., hats, shirt collars, brushes, combs, etc.). Unfed adult lice may survive up to 3 days away from the host. In general, the eggs hatch within a week and adult head lice have a lifespan of 1 to 2 days away from the host.
Body lice (Pediculus humanus corporis) are found on various parts of the body and are passed on through shared clothing or bedding. Unlike head lice, body lice attach their eggs to clothes fibres, particularly along inside seams and other areas of close body contact. A female body louse usually deposits 9 to 10 eggs per day, and a total of 270 to 300 eggs over her lifetime. The eggs are incubated by the person's body heat and hatch in about one week. Development time (egg to adult) takes about 3 to 5 weeks. Body lice may carry serious diseases such as epidemic typhus and trench fever.
Pubic lice (Phthirus pubis), commonly referred to as crabs, live on the skin and hair of the pubic area and are spread by sexual contact, shared clothing, and bedding. Pubic lice can also attach themselves to the eyelashes.
Head lice are found in most urban schools, where a few cases are reported every year, usually early in the fall when children return to school. Contrary to popular opinion, head lice can infect clean heads as often as dirty ones. They are more common in girls than in boys, although not necessarily more common in girls with long hair. Head lice do not carry disease.
Human lice are not transmitted from dogs, cats, or other pets.
Causes of Lice
Head lice are usually spread among children crowded together in urban daycare centres and primary schools. They have no wings, so they cannot jump or fly from person to person; they move by crawling quickly or by grasping a shaft of hair with tiny front claws and then swing from one hair strand to another. In this way, they travel by direct head-to-head contact when children play with their heads close together or indirectly through sharing hats, coat hooks, scarves, bike helmets, headphones, hairbrushes, toys, or bedding.
Poor hygiene does not play a role in head lice, although it does in body lice. Body lice are usually found among people in cramped, crowded conditions and mainly affect those living in military barracks, as well as poor and homeless people. They are generally rare today thanks to improved sanitation, frequent bathing, and changing of clothes.
Pubic lice are transmitted by sexual contact, mainly among adolescents and young adults, but also can be transmitted by sharing towels and through sheets and clothing.
Symptoms and Complications of Lice
The primary symptoms include:
- evidence of lice on the scalp, body, clothing, or pubic or other body hair
- intense itching
- nits on hair shafts
- small, red lesion at each new feeding site
A person may not experience any initial symptoms of head lice – the itching may not start until a week or two after the initial infestation. Some people never feel itchy at all.
Scratching is the cause of most complications due to lice, as it can cause abrasions that may lead to secondary infections. Some people with lice develop hives, scalp scabs, and enlarged neck nodes.
