Head Lice – Life Cycle, Types, Symptoms, Treatment, Prevention

What are Lice?

Lice are tiny gray-brown insects that live, grow, and feed on humans as parasites. It feeds on the host’s blood by piercing the skin of the host with its narrow anterior mouth parts. Lice may spread from one person to another through close contact or by sharing personal items and clothing. Dogs, cats, or other household pets are not involved in the transmission of human lice.

The most common type of lice infestation is head lice. Head lice infestation, though extremely unpleasant and embarrassing, does not help in spreading other diseases, or cause serious health problems. Lice infestation should be treated aggressively so as to get rid of the problem as well as to prevent recurrence.

Types of Lice Infestation

Lice infestation or pediculosis is a very common problem all over the world. There are 3 types of lice infestations.

• Head lice or pediculosis capitis is caused by Pediculus humanus capitis. This is a common problem, particularly among school children. The lice are tiny insects, about 3 mm long, with legs that are specially adapted to cling onto hair shafts. It lays eggs (nits) at the base of the hair fibers. The nits bind firmly to the scalp hairs and appear white when empty. Head lice are usually spread by close head-to-head contact and sharing hair grooming items.
• Body lice or pediculosis corporis is caused by Pediculus humanus corporis. These live, grow, and lay eggs in the seams of clothing. It is found on the body only when it feeds.
• Pubic lice, crab lice, or pediculosis pubis is caused by Phthiriasis pubis. These affect the pubic hairs and are usually sexually transmitted. The eyebrows, eyelashes, axillae (armpits), facial hair, chest hair, and very rarely the scalp hair may be involved in this type of lice infestation.

Life Cycle of Lice

There are 3 stages in the life cycle of the head louse – nit (egg), nymph, and adult. Once mating occurs, a female louse can lay around 50 to 100 eggs at the rate of 6 per day. The eggs are laid at the base of the hair shaft and are bound firmly to the hair by a glue-like substance till it hatches into nymphs, in about 6 to 10 days.

A louse reaches full maturity at around 10 days after hatching. The adult louse feeds about 5 times a day. It injects saliva which is an irritant to the skin and feeds by sucking blood. The lifespan of a female louse is about 1 month. The head lice will die within 2 days if it cannot feed on a human host.

Symptoms of Head Lice

The common symptoms are :

• Intense itching of the scalp, usually due to allergic reaction to lice bite. This occurs more frequently at night when the lice feed. Read more on other causes of itchy scalp.
• Tickling sensation when the lice move.
• Irritation of the scalp, especially a night.
• Reddish eruptions and sores on the head, especially on the nape of the neck.

People at Risk

• Head lice infestation is most common in pre-school and school children.
• Family members of such children are most likely to be affected as well.
• Anybody coming in close contact with another person suffering from head lice or sharing personal effects such as combs and clothing, may become infected as well.
• Contrary to popular belief, head lice do not occur due to poor hygiene, or only in people of low socio-economic status.
• Women are more likely to get head lice than men.

Treatment of Head Lice

To effectively treat head lice, the person infested as well as all close contacts, especially family members, with similar infestation should be treated simultaneously.

• Pediculicides are medications that kill head lice – over-the-counter (OTC) or prescription products can be used to treat head lice. It is important to follow the instructions closely. Resistance to treatment has become a problem.
• OTC products include shampoos containing pyrethrin or permethrin.
• Prescription medication, such as malathion, may be used when OTC products are ineffective. Malathion is more toxic and should be used with caution in pregnant and breastfeeding women.
• Lindane is not used as the first line of treatment because of its extreme toxicity.
• Ivermectin, a prescription drug, may be given orally in some resistant cases.
• In some cases, meticulous combing may be the only option for removal of head lice.
• Another option is application of benzyl alcohol lotion to the hair. This is usually kept on for about 10 minute and then rinsed off. Treatment is repeated after a week. Benzyl alcohol lotion is less toxic than the other pediculicides and may be used even in children 6 months or older.
• Calamine lotion and antihistamines in case of allergic reactions.
• Insecticides should not be used as prophylaxis (for prevention) of head lice.
• Head shaving may be considered when all other methods fail. The shaved off hair should be collected carefully in a plastic bag, sealed, and thrown in the garbage.
• After completion of treatment, pillows, bed sheets, towels, and clothing should be washed in hot water to kill lice. Combs and brushes should be soaked in hot water for over 5 minutes.
• Carpets, couches and other soft furnishing in the house should be vacuumed thoroughly.

Prevention of Head Lice

It may be difficult to prevent head lice in school-going children. Educating the child regarding sharing of combs and brushes may help minimally since lice spreads more often by direct head-to-head contact. Personal hygiene is not related to lice infestation. Being alert and taking immediate action if nits or lice are found on the hair can prevent further spread.