Abstract and Introduction
Pediculosis and scabies are caused by ectoparasites. Pruritus is the most common presenting symptom. Head and pubic lice infestations are diagnosed with visualization of live lice. Nits (lice eggs or egg casings) alone are not sufficient to diagnose a current infestation. A "no-nit" policy for return to school is not recommended because nits can remain even after successful treatment. First-line pharmacologic treatment for pediculosis is permethrin 1% lotion or shampoo. Newer treatments are available but costly, and resistance patterns are generally unknown. Noninsecticidal agents, including dimethicone and isopropyl myristate, show promise in the treatment of pediculosis. Extensive environmental decontamination is not necessary after pediculosis is diagnosed. In adults, the presence of pubic lice should prompt an evaluation for sexually transmitted infections. Body lice infestation should be suspected in patients with pruritus who live in crowded conditions or have poor hygiene. Scabies in adults presents as a pruritic, papular rash in a typical distribution pattern. In infants, the rash can also be vesicular, pustular, or nodular. First-line treatment for scabies is permethrin 5% cream. Clothing and bedding of persons with scabies should be washed in hot water and dried in a hot dryer. Counseling regarding appropriate diagnosis and correct use of effective therapies is key to reducing the burden of lice and scabies.
Pediculosis and scabies are caused by ectoparasites. Pruritus is the most common presenting symptom with both conditions. Determining the specific etiology of pruritus based on history and physical examination findings is important. Lice in particular may be overdiagnosed by anxious patients and treated using over-the-counter medications without an office evaluation. Seeking an appropriate clinical diagnosis may help reduce treatment-resistant lice. Although the diagnosis of pediculosis and scabies has not changed substantially, there are new developments in treatment since this topic was previously covered in American Family Physician.[2–4]
Lice are obligate, blood-sucking parasites that can infest the human head (Pediculus humanus capitis; Figure 1), body (Pediculus humanus corporis), and pubic region (Phthirus pubis; Figure 2). Body and head lice are approximately 1 to 3 mm long, about the size of a sesame seed, and are flattened dorsoventrally. The pubic louse is much shorter. Because lice cannot jump or fly, transmission requires close contact. The female louse can survive for up to one month on the scalp and lay up to eight to 10 eggs per day at the skin-hair junction. The eggs hatch and mature into adults in 20 days. Viable eggs may be difficult to see but can be found attached to the base of hairs. The yellow to white empty egg casings are easier to visualize.
Adult Pediculus humanus capitis (head louse). Body and head lice are approximately 1 to 3 mm long and are flattened dorsoventrally.
Illustration by Myriam Kirkman-Oh
Reprinted with permission from Flinders DC, De Schweinitz P. Pediculosis and scabies. Am Fam Physician. 2004;69(2):341.
Adult Phthirus pubis (pubic louse). An egg can be seen within the body cavity. Pubic lice are much shorter than head lice.
Reprinted from the Centers for Disease Control and Prevention's Laboratory Identification of Parasites of Public Health Concern.
Am Fam Physician. 2019;99(10):635-642. © 2019 American Academy of Family Physicians