Human lice (Pediculus humanus) are world-wide, obligate, wingless ectoparasites that spend their entire life cycle on humans; the medical term condition of being infested with lice is pediculosis. This species is comprised of two morphologically identical, interbreeding (at least in laboratory conditions, although not in natural ones), but behaviorally distinguishable subspecies that occupy non-overlapping habitats: Pediculus humanus humanus (human body lice; also known as Pediculus humanus corporis) and Pediculus humanus capitus (human head lice). These subspecies are thought to have diverged about 110,000 years ago when humans started wearing clothing.
As their name suggests, body lice, sometimes nicknamed "seam squirrels," are found hiding in and attaching their eggs to clothing, whereas head lice inhabit the scalp and attach their eggs at the base of hairs. Body lice infest mostly those living with poor hygiene and who do not have access to bathing facilities or clean sheets and clothes, as infestations do not persist through bathing and laundering. These lice can carry such diseases as louse-borne typhus (Rickettsia prowazeki), trench fever (Rochalimaea Quintana), and louse-borne relapsing fever (Borrellia recurrentis). Head lice, on the other hand, are not known to be disease vectors.
(Morgan 2001; Smith; Wikipedia 2011a, 2011b)
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