The body louse is morphologically very similar to the head louse and the two species were until recently treated as two subspecies, P. humanus humanus (synonym: P. humanus corporis) and P. humanus capitis. However, the biology and medical importance of the two species are distinctly different. The primary microhabitat for all stages of the body louse is the clothes of humans. The blood-feeding stages (i.e. all stages except the eggs) only leave the clothes of its host in order to blood-feed on the host's skin. Each individual louse feeds about four times in 24h. The gravid female body louse usually glues her eggs to fibres in the seams. On rare occasions, she may attach eggs onto body hairs. The body louse is present in all parts of the world on persons who live under poor hygienic conditions and who cannot wash or change their clothes regularly. Thus, infestations with body lice are associated with poverty, very poor hygienic conditions, and (often) a cold climate where people need to wear clothes. In the tropics, the presence of the body louse is concentrated to relatively cold areas such as the highlands of Ethiopia and the South American Andes where people wear clothes on the greater part of the body. In such areas, the heaviest infestations usually occur during the coldest part of the year. In Europe and the former Soviet Union, during the Second World War, the body louse populations had excellent opportunities to increase due to the extremely unhygienic conditions in concentration camps, prisons, refugee camps, etc. Then, the body louse became a relatively rare species. However, with the vast economic and social changes that have now taken place in, for example, eastern Europe and Russia, an increasingly greater part of the human population in these areas have become extremely poor and even homeless. Therefore, the possibilities for the body louse to find optimal living conditions have greatly increased. In a recent investigation involving 300 homeless men in Moscow, 19% were positive for body lice (or eggs); 3-25 lice per person were recorded from their clothes; 12% of 268 louse samples were positive by polymerase chain reaction (PCR) for Bartonella quintana (Rydkina et al. 1999).
In contrast to the head louse, the body louse is an extremely important vector of human-pathogenic microorganisms. In Russia, louse-transmitted diseases have caused more deaths than any other infectious disease in recent centuries (Rydkina et al. 1999). Louse infestations are promoted by wars and natural disasters when people are forced into crowded, unhygienic conditions. Thus, outbreaks of louse-borne diseases is a constant threat to people living under primitive conditions such as those prevailing during conditions of war, in refugee camps and in prisons in poor countries. The body louse is the vector of three medically important infections, namely, epidemic typhus caused by Rickettsia prowazekii, trench fever caused by Bartonella quintana, and epidemic relapsing fever caused by Borrelia recurrentis.
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