Pediculosis

Pediculosis is caused by parasitic forms of lice: Pediculus humanus var. capitis causes pediculosis capitis (head lice); Pediculus humanus var. corporis causes pediculosis corporis (body lice); and Phthirus pubis causes pediculosis pubis (crab lice). These lice feed on human blood and lay their eggs (nits) in body hairs or clothing fibers.

After the nits hatch, the lice must feed within 24 hours or die; they mature in about 2 to 3 weeks. When a louse bites, it injects a toxin into the skin that produces mild irritation and a purpuric spot. Repeated bites cause sensitization to the toxin, leading to more serious inflammation. Treatment can effectively eliminate lice.

Causes

P. humanus var. capitis (most common species) feeds on the scalp and, rarely, in the eyebrows, eyelashes, and beard. This form of pediculosis is caused by overcrowded conditions and poor personal hygiene, and commonly affects children, especially girls. It spreads through shared clothing, hats, combs, and hairbrushes.

P. humanus var. corporis lives in the seams of clothing, next to the skin, leaving only to feed on blood. Common causes include prolonged wearing of the same clothing (which might occur in cold climates), overcrowding, and poor personal hygiene. It spreads through shared clothing and bed sheets.

P. pubis is primarily found in pubic hairs, but this species may extend to the eyebrows, eyelashes, and axillary or body hair. Pediculosis pubis is transmitted through sexual intercourse or by contact with clothes, bed sheets, or towels harboring lice.

Signs and symptoms

The first indication of an infestation is usually itching at the back of the head and around the ears. Itching in these areas should lead to an examination of the scalp for louse nits (eggs). Severe scratching may result in secondary bacterial infection in these areas. Head lice do not carry or spread disease.

Diagnosis

Pediculosis is visible on physical examination as follows:

• pediculosis capitis: oval grayish nits that can't be shaken loose like dandruff (the closer the nits are to the end of the hair shaft, the longer the infection has been present, because the ova are laid close to the scalp)
• pediculosis corporis: characteristic skin lesions; nits found on clothing
• pediculosis pubis: nits attached to pubic hairs, which feel coarse and grainy to the touch.

Treatment

Pediculosis is treated with anti-lice creams, lotions, or shampoos applied to affected body parts, according to instructions. Examples include:

1. Permethrin (Nix, Elimite): single application.
2. Pyrethrins (Rid, R and C, A-200): reapply in 7 days.
3. Lindane (Kwell, by prescription): reapply in 7 days.

Side effects of treatment, such as skin irritation or body absorption of the medication, can occur but are usually related to more frequent medication applications than recommended. All anti-lice preparations are toxic, but they are safe if used according to the directions. Keep all preparations out of the eyes and out of the reach of children.

The DOs

1. Examine household members and close contacts for lice, and treated if infestation exists. Nits can be removed with a fine-tooth comb.
2. Personal items such as combs or brushes should be soaked in hot water for 15 minutes.
3. Clothes and bedding should be washed in hot water and dried in a dryer; or alternately, clothes and linen can be ironed, or sealed in a plastic bag for 10 days.

The DON'Ts

1. Do not use medication more frequently than recommended.

Prevention

Avoid physical contact with infested individuals and their belongings, especially clothing, headgear, brushes, combs and bedding. Combs and brushes used on infested persons should be immersed in hot water (>130° ), Lysol®, rubbing alcohol or a lice-killing chemical for 1 hour. Floors, rugs, pillows and upholstered furniture should be thoroughly vacuumed, and the vacuum bag discarded when complete. Clothing, linen and cloth toys worn or handled by an infested individual within 2 days of being diagnosed with head lice should be washed in hot water (>130°F) or machine dried at the hottest setting for 20 minutes. Other articles may be dry cleaned or sealed in plastic bags for at least 10 days to destroy lice and eggs. In addition, parents should perform regular lice checks on the scalp of children who attend school and day care centers, especially when excessive itching is noticed. Fogging with insecticides or spraying the environment with lice-killing chemicals is not recommended.