Body louse

The body louse (Pediculus humanus humanus, sometimes called Pediculus humanus corporis) is a louse which infests humans. The condition of being infested with head lice, body lice, or pubic lice is known as pediculosis.

Origins
Genetic analysis suggests that the human body louse may have originated about 107,000 years ago from the head louse after the invention of clothing, with the ancestor of all human lice emerging about 770,000 years ago.

Entomology and pathology
Pediculus humanus humanus (the body louse) is indistinguishable in appearance from Pediculus humanus capitis (the head louse) and under laboratory conditions they will interbreed. In their natural state, however, the two subspecies do not interbreed and occupy different habitats. In particular, body lice have evolved to attach their eggs to clothes, whereas head lice attach their eggs to the base of hairs.

Body lice frequently lay their eggs on or near the seams of clothing. Body lice must feed on blood and usually only move to the skin to feed. Body lice exist worldwide and infest people of all races. Body lice infestations can spread rapidly under crowded living conditions where hygiene is poor (homeless, refugees, victims of war or natural disasters). In the United States, body lice infestations are rare, typically found mainly in homeless transient populations who do not have access to bathing and regular changes of clean clothes. Infestation is unlikely to persist on anyone who bathes regularly and who has at least weekly access to freshly laundered clothing and bedding.

Body lice are spread through prolonged 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.

Body lice are a nuisance in themselves and cause intense itching. They are however, also vectors (transmitters) of other diseases. Body lice can spread epidemic typhus, trench fever, and louse-borne relapsing fever. Although louse-borne (epidemic) typhus is no longer widespread, outbreaks of this disease still occur during times of war, civil unrest, natural or man-made disasters, and in prisons where people live together in unsanitary conditions. Louse-borne typhus still exists in places where climate, chronic poverty, and social customs or war and social upheaval prevent regular changes and laundering of clothing.

Life stages
Body lice have three forms: the egg (also called a nit), the nymph, and the adult.


 * 1) Nits are lice eggs. They are generally easy to see in the seams of an infested person’s clothing, particularly around the waistline and under armpits. Body lice nits occasionally also may be attached to body hair. They are oval and usually yellow to white in color. Body lice nits may take 1–2 weeks to hatch.
 * 2) A nymph is an immature louse that hatches from the nit (egg). A nymph looks like an adult body louse, but is smaller. Nymphs mature into adults about 9–12 days after hatching. To live, the nymph must feed on blood.
 * 3) The adult body louse is about the size of a sesame seed, has 6 legs, and is tan to greyish-white. Females lay eggs. To live, lice must feed on blood. If a louse is separated from its person, it dies at room temperature.

Treatment
A body lice infestation is treated by improving the personal hygiene of the infested person, including assuring a regular (at least weekly) change of clean clothes. Clothing, bedding, and towels used by the infested person should be laundered using hot water (at least 130 F) and machine dried using the hot cycle.

Sometimes the infested person also is treated with a pediculicide (a medicine that can kill lice); however, a pediculicide generally is not necessary if hygiene is maintained and items are laundered appropriately at least once a week. A pediculicide should be applied exactly as directed on the bottle or by a physician.

Delousing can also be practically achieved by boiling all clothes and bedding, or washing them at a high temperature. A temperature of 130 F for 5 minutes will kill most of the adults and prevent eggs from hatching. Leaving the clothes unwashed, but unworn for a full week, also results in the death of lice and eggs.

Where this is not practical or possible, powder dusting with 10% DDT, 1% malathion or 1% permethrin is also effective. Oral ivermectin at a dose of 12 mg on days 0, 7 and 14 has been used in a small trial of 33 people in Marseilles, but did not result in complete eradication, although there was a significant fall in the number of parasites and proportion of people infected. At the moment, ivermectin cannot be routinely recommended for the treatment of body lice.

Medication, insecticide or burning of clothing and bedding is usually not necessary, as the problem normally goes away with daily bathing, weekly (or more frequent) laundering and drying of clothing, bedding, towels, etc. in a hot clothes drier.