The human itch mite, Sarcoptes scabiei var. hominis.
Through prolonged skin-to-skin contact with a person with conventional scabies or via brief skin-to-skin contact with a person with crusted (Norwegian) scabies (a more severe form of scabies in which a person is infested with a large number of mites). Indirect transmission may occur through contact with objects contaminated by a person with crusted (Norwegian) scabies but is rare if the person has conventional scabies.
Scabies occurs worldwide. It is transmitted most easily in settings where skin contact is common. Crusted (Norwegian) scabies most commonly occurs among elderly, disabled, debilitated, or immunosuppressed people.
Symptoms occur 2–6 weeks after a person is first infested. However, if someone has had scabies before, symptoms appear much sooner (1–4 days after exposure). Conventional scabies is characterized by intense itching, particularly at night, and by a papular or papulovesicular, erythematous rash. Crusted (Norwegian) scabies is characterized by widespread crusts and scales that contain large numbers of mites, although itching may be less than in conventional scabies.
Generally diagnosed by identifying burrows in a patient with itching and by observing the characteristic rash. Diagnosis can be confirmed by microscopically identifying mites, mite eggs, or scybala (mite feces).
Permethrin (5%) cream is considered by many to be the drug of choice. Ivermectin is reported to be safe and effective to treat scabies, including crusted (Norwegian) scabies. It is not FDA-approved but should be considered for patients in whom treatment has failed or who cannot tolerate other approved medications.
Avoid prolonged skin-to-skin contact with people who have conventional scabies and even brief skin-to-skin contact with people who have crusted (Norwegian) scabies. Contact with items such as clothing and bed linens that have been used by an infested person should be avoided, especially if the person has crusted (Norwegian) scabies.
American Academy of Pediatrics. Scabies. In: Pickering LK, editor. Red Book: 2012 Report of the Committee on Infectious Diseases. 29th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2012. p. 641–3.
Chosidow O. Clinical practices. Scabies. N Engl J Med. 2006 Apr 20;354(16):1718–27.