Scabies

Scabies is an infestation of the skin with the microscopic mite Sarcoptes scabei. Infestation is common, found worldwide, and affects people of all races and social classes. Scabies spreads rapidly under crowded conditions where there is frequent skin-to-skin contact between people, such as in hospitals, institutions, child-care facilities, and nursing homes.

The mites that cause scabies burrow into the skin and deposit their eggs, forming a characteristic burrow that looks like a pencil mark. Eggs mature in 21 days. The itchy rash is an allergic response to the mite. Caused by the mite Sarcoptes scabiei, variety hominis, it produces intense, itchy skin rashes when the impregnated female tunnels into the stratum corneum of the skin and deposits eggs in the burrow. The larvae, which hatch in 3-10 days, move about on the skin, molt into a "nymphal" stage, and then mature into adult mites. The adult mites live 3-4 weeks in the host's skin.

The motion of the mite in and on the skin produces an intense itch which may resemble an allergic reaction in appearance. The presence of the eggs produces a massive allergic response which, in turn, produces more itching. Once away from the human body, mites do not survive more than 48-72 hours. When living on a person, an adult female mite can live up to a month. Scabies is transmitted readily, often throughout an entire household, by prolonged skin-to-skin contact with an infected person (e.g. bed partners), and thus is sometimes classed as a sexually transmitted disease. Spread by clothing, bedding or towels is a less significant risk, though possible.