Skin infestation by the mite Sarcoptes scabiei, causing itching.
Transmission of the mite occurs by skin–skin contact with an infested individual or contaminated clothing or bedding. The mite burrows down into the stratum corneum of the skin and then the female lays eggs.
There is often a widespread, erythematous urticating rash all over the body as a result of a hypersensitivity reaction to the mite. Patients present with severe itching usually worse at night.
On examination small papules and linear tracks, caused by burrowing mites, are seen around the wrists, finger webs and ankles (and scrotum in the male).
In immunosuppressed patients, Norwegian/crusted scabies may occur with diffuse scaly erythematous patches especially on the scalp, hands and feet.
The burrows and distribution pattern is very suggestive of the diagnosis. The mite can be visualised using a dermatoscope.
Patients are extremely infectious and require barrier nursing. The entire skin except the face should be treated with malathion or permethrin. All close contacts require treatment, and clothing and bed linen should be thoroughly machinewashed. Norwegian/crusted scabies may require repeated treatments.