Pediculosis corporis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Life Cycle
The life cycle of the body louse Pediculus humanus humanus, has three stages: egg, nymph, and adult.[1]
- Nits are body lice eggs. They are hard to see and are often confused for dandruff. Nits are laid by the adult female and are cemented at the base of the hair shaft nearest the skin . They are 0.8 mm by 0.3 mm, oval and usually yellow to white.
- Nits take about 1 week to hatch (range 6 to 9 days). Viable eggs are usually located within 6 mm of the skin.
- The egg hatches to release a nymph.
- The nit shell then becomes a more visible dull yellow and remains attached to the hair shaft. The nymph looks like an adult body louse, but is about the size of a pinhead.
- Nymphs mature after three molts and become adults about 7 days after hatching.
- The adult louse is about the size of a sesame seed, has 6 legs (each with claws), and is tan to grayish-white. In persons with dark hair, the adult louse will appear darker. Females are usually larger than males and can lay up to 8 nits per day. Adult lice can live up to 30 days on a person’s body.
- To live, adult lice need to feed on blood several times daily. Without blood meals, the louse will die within 1 to 2 days off the host.
Transmission
Body lice are spread through direct physical contact with a person who has body lice or through contact with articles such as clothing, beds, bed linens, or towels that have been in contact with an infested person. In the United States, actual infestation with body lice tends to occur only in persons, such as homeless, transient persons, who do not have access to regular (at least weekly) bathing and changes of clean clothes.
Associated Diseases
- Typhus
- Louse-borne relapsing fever