• Infestation by Sarcoptes scabiei var. hominis, a mite that lives within the stratum corneum of human skin (Fig. 71.1).

• Transmission is primarily by direct contact with an infested person and occasionally by fomites (e.g. clothing); incubation period may be up to 6 weeks; in some tropical regions, scabies can infest the majority of individuals in a community.

• Asymptomatic infestation by scabies is not uncommon (‘carriers’ of scabies).

• In symptomatic cases, pruritus is severe, often worse at night or after a hot shower; secondary bacterial infections (e.g. staphylococcal, streptococcal) may occur.

• Skin lesions are variable and include erythematous papules with scale-crust, small patches of eczema, excoriations, vesicles (especially acrally in infants), and nodules; the classic burrow – a thread-like, grayish-white, wavy, 1- to 10-mm linear structure – favors acral sites (Figs. 71.2 and 71.3).

• Clinical confirmation is by mineral oil examination of skin scrapings (see Chapter 2) or dermoscopy (see Fig. 71.2D).

• Usually <100 mites, but often no more than 10–15, living on an infested individual (Fig. 71.4); there may be thousands of mites in crusted scabies (thick scale, especially acrally, with minimal inflammation), which affects immunocompromised hosts, those with altered skin sensation, and sometimes the elderly (Fig. 71.5).

• In general, the mites live off the body ≤3 days; if accompanied by sloughed skin, as in crusted scabies, the duration may be longer.

• DDx: arthropod bites, including bites of animal mites (e.g. Cheyletiella); diseases associated with generalized pruritus (e.g. atopic dermatitis; see Table 4.1); in infants, infantile acropustulosis, which may also occur following successful treatment of scabies.

• Rx: see Table 71.1.

– Two overnight applications of a topical antiscabetic medication, 1 week apart, to the entire body surface from the neck down to the toes; in infants, the elderly, and the immunocompromised, need to include the face and scalp.

– Permethrin 5% cream is the preferred topical agent.

– Oral ivermectin (200–400 microg/kg given on days 1 and 8) is increasingly replacing topical medications, especially when large groups of individuals are affected as in a nursing home.

– All clothing and bedding should be washed in hot water and dried with high heat, or stored in a bag for 10 days (3 days after the second treatment).

– All family members and close contacts should be treated simultaneously, even if asymptomatic.

– Pruritus and cutaneous lesions often last 2–4 weeks after successful treatment, but patients may feel relief within 3 days.