Signs Symptoms and Diagnosis

Head lice primarily infest children but do affect all ages (19). Of interest, in the Americas, blacks are less affected than others, whereas the reverse is true in Africa (20). A red, maculopapular rash on the scalp, the nape of the neck, and the shoulders may occasionally result, but most infestations lack symptoms. Excoriation may yield crust, matted hair, and bacterial infection. Eggs or nits are more easily found than lice; hair casts, seborrheic material, and other debris can closely mimic nits (21). Direct contact, not shared headgear and grooming implements, now appears to be the primary means of louse transfer. Treatment should only be performed when live lice are discovered; if live nits are found by a specialist (primary care physicians should not attempt to discriminate live from dead nits), treatment should also be initiated.

Body lice mainly infest indigent people who remain clothed for extended periods. The lice remain sequestered in the seams and between layers of clothing except when feeding (22). They are transmitted both by direct contact and by exchange of contaminated clothing and bedding. Body louse saliva induces an intensely pruritic, red, maculopapular eruption hours to days after feeding, often resulting in hives complete with flare and wheal formation. Excoriation can yield crusts, regional adenopathy, and bacterial infection. The saliva can itself induce a hemorrhagic reaction. Chronic infestation can incite lichenification with generalized hyperpigmentation, known as vagabond's disease.

Pubic louse saliva yields a pruritic rash mainly in pubic, inguinal, and lower abdominal sites, and occasionally also axillae and eyelids. The rash may present as blue-gray macules known as maculae ceruleae (23). Excoriation can yield crusts, but infection is less likely than with other lice. Nits are always present, and the lice can usually be seen with a magnifying lens. Infested eyelids have blepharoconjunctivitis with occasional serosanguinous discharge, and occasional adult lice at the eyelash roots. The diagnosis mandates considering other venereal diseases and evaluating all sex partners.

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