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Pediculosis
Key Points
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Blood-sucking parasites specialized to certain types of human hair.
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Body but not hair lice transmit typhus and trench fever.
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Highest prevalence is in Caucasians owing to their more cylindrical hair structure.
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Nits are cemented to hair shafts predominantly on the retroauricular occiput.
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Lice combs are useful for diagnosis.
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Intense pruritus is common.
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Body and crab lice may cause maculae ceruleae.
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Treatment with topical permethrin, ivermectin, and dimethicones is successful.
Introduction
Infestation by sucking lice causes pediculosis. Pediculus humanus capitis , P. humanus humanus , and Pthirus pubis are the three types of lice that commonly parasitize humans. They are in the phylum Arthropoda, class Insecta, order Phthiraptera, suborder Anoplura, and family Pediculidae or Pthiridae. P. humanus humanus , the body louse, and P. humanus capitis , the head louse, are variants of the same species.
History
Lice have infested humans for thousands of years, and pediculosis remains a prevalent disease in affluent suburban schools as well as in inner-city populations. Despite the similarities between body lice and head lice, body lice (but not head lice) transmit typhus, trench fever, and relapsing fever. Interestingly, Rickettsia prowazekii and Bartonella quintana can be isolated from body lice and used not only in the epidemiologic study of epidemic typhus and trench fever but also in the prediction of disease outbreaks in refugee populations. Human DNA extracted from lice can be used as forensic evidence.
Epidemiology
Pediculosis Capitis
P. humanus capitis infests the scalp of humans and affects 6–12 million people per year in the USA alone. Infestation occurs in all seasons, but may be increased in warmer months. Head lice predominantly affect females aged 3–12 in the pediatric population. Close head-to-head contact is thought be the most important mode of transmission, but contact with infested fomites can also spread lice. The anatomy of head lice adapts them to grasp better the more cylindrical hairs of Caucasians. This fact, in combination with factors such as the use of hair pomades, results in a lower incidence of pediculosis in African–Americans.
Pediculosis Corporis
P. humanus humanus is the cause of pediculosis corporis. Body lice transmit three diseases: louse-borne relapsing fever, epidemic typhus, and trench fever. R. prowazekii , the organism of epidemic typhus, has been isolated from body lice in Burundi, France, Peru, Russia, and Zimbabwe ; Russia and Burundi have both documented outbreaks. In the USA, a natural endemic reservoir of R. prowazekii is found in North American flying squirrels ( Glaucomys volans and sabrinus ). Following a natural disaster, typhus has the potential to spread from an endemic source and become a louse-borne epidemic. Body lice can carry and transmit both R. prowazekii and B. quintana simultaneously. In developed countries, pediculosis corporis most commonly affects the urban homeless, and infestation correlates with blood serologies for B. quintana .
Pediculosis Pubis
Infestation with Phthirus pubis is commonly acquired sexually. Patients should be screened appropriately. Infestation is year-round, but slightly increased in colder months.
Pathogenesis and Etiology
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