Definition of Pediculosis

Pediculosis – Infestation with lice, parasites that live on the skin and feed by sucking blood through small punctures they make through the skin. Lice attach their eggs, called nits, to hair shafts. Of the numerous species of lice, three afflict humans:

  • Pediculus humanus capitis, which infests the scalp
  • Pediculus humanus corporis, which infests the body
  • Pediculus pubis, which infests the pubic region

Each species has unique claw and mouth structures that allow survival in the particular region of the body, and each species can infest only the body region for which it is adapted. However, infestation with two or more species is common. Pediculosis refers collectively to infestation with any species of lice, and affects around 12 million Americans each year.

Pediculosis spreads easily through direct and indirect contact, and is so common among schoolage children that schools routinely screen for its presence. Crowded environments, such as schools and dormitories, allow close contact between people, permitting the lice to spread from one person to another.

Pediculosis may be present for as long as two months before causing appreciable symptoms, increasing the potential for extending infestation. Head and pubic lice and nits resist the most scrupulous cleansing.

Infrequent clothing changes are often a factor with body lice infestation. Poor personal hygiene such as infrequent bathing can allow secondary problems such as infection to develop.

Symptoms of Pediculosis and Diagnostic Path

The most common symptom of pediculosis is itching, which is often particularly intense at night when the lice feed. The saliva of the lice contains enzymes to delay coagulation (blood clotting) which irritate the skin. The bites leave reddened papules (raised bumps) that continue to itch. Finding nits (eggs attached to hair shafts) is the conclusive diagnostic marker.

Nits are difficult to remove, which helps distinguish them from other matter that might collect on the skin or hair, as well as from conditions such as seborrheic dermatitis and common dandruff. Examination with fluorescence (Woods lamp) causes the lice and nits to glow yellow or green.

Pediculosis Treatment Options and Outlook

Treatment for head or pubic infestation combines removing the nits with a fine-tooth comb (nit comb) and shampooing or washing with an insecticide-based product such as permethrin (Nix) or malathion (Ovid). Multiple treatments about a week apart for a month, or until no nits are present, are necessary to cover the lifespan of the louse, which is about 35 days.

It is important to carefully follow the label directions for the product and to leave the product on the hair or skin for the instructed length of time. Most treatment regimens include combing the hair with a nit comb after shampooing. All individuals in the household should receive treatment.

It is also necessary to wash clothing and bed linens in hot water (130ºF or more) for at least five minutes, and placing stuffed toys in sealed plastic bags for two weeks. The hot water wash kills any lice or nits, and the plastic bag method deprives any lice or nits that hatch of nourishment. Because body lice live on the clothing rather than the skin, washing the clothing in hot water is usually adequate.

Pediculosis Risk Factors and Preventive Measures

Most pediculosis leaves no residual health consequences, although secondary infections may develop with excessive scratching. However, sexual contact generally transmits pubic pediculosis, which raises concern for sexually transmitted diseases (STDS). Body lice (P. humanus corporis) can carry serious bacterial diseases including typhus.


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