Scabies

Scabies is an infestation of the epidermis by the mite *Sarcoptes scabiei*. The mite and its products—especially saliva, eggs, and feces—activate a delayed immune response. That response, rather than the small number of mites in ordinary scabies, produces the disproportionate itching and papular rash. The itch is often most intense at night. Warmth in bed can make the sensation more noticeable, but nocturnal pruritus is also a useful diagnostic clue. A person with a first infestation may not itch immediately; a sensitised person may react much sooner if reinfested. Transmission is mainly through prolonged close skin-to-skin contact. Household members and sexual contacts are common sources, and a person can spread scabies before recognising the rash. Crusted scabies is different in degree and in infection-control importance: thick hyperkeratotic crusts contain a much larger mite burden and can spread readily through contact with shed skin or contaminated items. It is more likely in people with impaired immunity, although anyone with crusting requires prompt assessment. Scabies is not a consequence of poor personal hygiene. The relevant risk is exposure to an infested person...