Lice (Pediculosis, Crabs)

Lice are tiny parasitic insects that live on blood. In humans, they infest primarily the scalp, hair, and genital area, but also other parts of the body. The most common types are:

• Head lice (Pedtculus humanus capitis), usually less than 1/8th of an inch long and almost as wide. They are most often spread through direct contact, but can also be picked up by sharing brushes, combs, and other head gear. Schools are a common source of outbreaks because lice spread easily on hats, scarves, and jackets in coat closets.
• Pubic lice (Phfhirus pubis), shorter and fatter than head lice. Their resemblance to tiny crabs, complete with claws, has given rise to their popular name, "crabs." They are usually transmitted by sexual contact.
• Body lice (Pcdiculus human us corporis), longer and thinner than pubic lice. Infestation is common among people who live in crowded, unsanitary conditions.

Although unpleasant, head and pubic lice don't carry disease, whereas body lice may transmit typhus, relapsing fever, and other disorders.

In all lice infestations, the primary symptom is intense itching, a reaction to the insect's saliva. Head lice tend to cause itching behind the ears and along the hair line at the back of the neck. Pubic lice, which sometimes also infect beards and eyebrows, typically produce itching in the genital area. Itching from body lice occurs mostly on the shoulders, trunk, buttocks, and abdomen.

Diagnostic Studies and Procedures

Detection is based on spotting the parasites. Although lice can be observed with the eye, a magnifying glass may be needed to tell one type from another. Head lice also leave telltale eggs, or nits, which appear as tiny, silvery clumps attached to the hair shaft near its root. They are easy to differentiate from dandruff because the nits do not flake off, but are virtually cemented to the hair shaft and must be removed by combing. Pubic lice also leave eggs attached to the base of pubic hairs. Body lice and their eggs tend to live in the seams of underclothing rather than on the skin.

Medical Treatments

Until recently, the preferred treatment for all types of lice infestations was lindane (Kwell), a DDT-derivative available as a prescription shampoo, cream, or lotion. Although lindane is highly effective, its use has become controversial because of the risk of central nervous system damage and other side effects. Most experts now recommend reserving Kwell for severe infestations that cannot cleared up by safer non-prescription products. If you are using Kwell, be sure to follow your doctor's instructions to the letter.

In some cases, itching is so severe that an antipruritic medication is necessary. For this problem, a doctor may prescribe a topical steroid or an oral medication such as clemastine (Tavist).

Alternative Therapies

Herbal Medicine. Although herbal therapy cannot destroy lice, such preparations as capsules of stinging nettle extract can ease severe itching.

Self-Treatment

In recent years, researchers discovered that chrysanthemums produce pyrethrin, a natural pesticide, that is deadly to all types of lice yet safe for humans. Today, non-prescription pyrethrin shampoos, available at pharmacies, are as effective as lindane while being much safer, especially for children. Start by killing adult lice with a pyrethrin shampoo, following package directions carefully. Then use a fine-toothed metal comb to remove eggs bonded to the hair shaft. Part wet hair into sections and carefully comb, from base to tip, one-inch wide tufts. Wipe nits from the comb frequently. A week to 10 days later, repeat the entire process. If lice have settled on the eyelashes, applying petroleum jelly three or four times a day should banish them within a week. (If this technique fails, consult your doctor; do not apply pyrethrin or any other lice-killing product around the eyes.)

Body lice are eliminated by bathing and discarding or fumigating infested clothing. To prevent re-infestation of all types of lice, you must rid your home of the pests. While adult head and body lice die after 48 hours without a blood meal, nits may not hatch until a month later, restarting the infestation. To avoid this, wash all personal clothing, bed linens, and other potentially infested items in hot water (at least 130°F or 49°C) and put them in a hot clothes dryer for at least 20 minutes. Dry cleaning also kills lice and nits. Disinfect combs and brushes, vacuum upholstered furniture and rugs.

Although self-treatment clears up most lice infestations, see your physician if scratching has caused open, infected sores. To alleviate itching, try soaking in a bath containing cornstarch or colloidal oatmeal. Also, consult a doctor if a child under the age of two years is infested or if over-the-counter treatment has been ineffective.

Other Causes of Itching

There are many causes of itching skin. Conditions to rule out include scabies, which is also produced by a skin parasite; ringworm and other fungal infestations; and skin allergies.