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Lice

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  1. Species, life cycle, and distribution
  2. Clinical aspects
  3. Treatment and prevention
  4. Conclusion
  5. References

Lice are small wingless insects that are ectoparasites of mammals. They are mostly host specific, and two species are human parasites: Pthirus pubis (pubic louse) and Pediculus humanus, with two varieties, P. h. capitis (head louse) and P. h. corporis (body louse). They are obligatory parasites, subsisting on blood from the host, and have mouthparts modified for piercing and sucking. The mouthparts are drawn into the head of the louse when not in use.
The adult head louse is about 2 to 4 mm long with an elongated body that is flattened dorsoventrally. The head is only slightly narrower than the thorax. The three pairs of legs are about equal in length and possess delicate hooks at the distal extremities. The entire life is spent on the host's body. The eggs (nits) are deposited on hair shafts, generally one nit to a shaft. The nits hatch in about 1 week, and the freshly hatched larvae, which must feed within 24 hours of hatching or die, mature in about 15 to 16 days. The adult female lives for approximately 1 month and may deposit more than 100 eggs during her reproductive life. Body lice are slightly larger than head lice but are similar in appearance with a similar life cycle, although the nits are deposited on fibers of clothing. Head lice and body lice interbreed.

[...] These lice leave clothing to feed on the skin or remain attached to the clothing while feeding, and thus they are most abundant where clothing abuts the skin (e.g., beltline). The bite results in a small red macule with a characteristic central hemorrhagic punctum. Excoriations, crusts, eczematization, and other secondary lesions generally obscure the primary lesions by the time the victim seeks medical attention. Shoulders, trunk, and buttocks are favorite sites for bites, and parallel scratch marks on the shoulders are a common finding. [...]


[...] If lice or nits are found after 7 days, retreatment is indicated. Family members and contacts should be treated simultaneously. Hats and scarfs should be machine washed with hot cycle and bed clothing dry-cleaned. Other pediculicides are available if the lice are resistant. Two products, RID (Pfizer, New York, N.Y.) and Triple X (Young's Drug Product, Weatherfield, Conn.) contain pyrethrins and piperonyl butoxide. One application of either preparation usually eradicates both lice and nits. A few persons may require another application 7 days after the initial treatment. [...]

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