Lice

Louse infestations comprise head lice (Pediculusis humanus capitis), body lice (Pediculusis humanus humanus), and pubic lice (Pthirus pubis) (10). The dorsoventrally flattened animals lack wings and infest only humans, although humans may be transiently affected by lice from other animals. The louse mouth is a toothed tubular structure that emerges from the head only when feeding begins; blood, the sole nutritional source, is obtained through a pair of stylets; a third stylet injects antigenic and antihemostatic saliva into the skin. During feeding copious defecation occurs, permitting transmission of louse-borne infectious diseases, such as typhus.

Head and body lice bear three clearly demarcated body regions, including a central thorax with six clawed legs and seven abdominal segments with lateral lobes. The crablike pubic louse, about as broad as it is long, is shorter than other lice, bears a more-fused body, and has slender claws on its forelegs, enabling it to grasp pubic hairs with ease; but they can also grasp eyelash, facial, axillary, and, rarely, scalp hairs.

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