Scabies is a skin disease caused by the mite Sarcoptes scabiei, which is a parasite that burrows into, resides and reproduces in human skin. It affects people of all ages, but the elderly or people with weakened immunity are more susceptible. Scabies can spread rapidly in crowded conditions, hence outbreaks of scabies have been reported in institutional settings such as hospitals, child-care facilities, hostels and elderly homes.
The most common symptom of scabies is intense itchiness which is more severe at night or after a bath. Rashes, thread-like lesions or vesicles may also be seen on the skin. The commonly affected areas are finger webs, wrists, elbows, armpits, nipples, lower abdomen, external genitalia, buttocks and shoulder blades. The face and scalp are usually spared, except in infants, young children and immunocompromised persons.
A severe form of scabies known as Norwegian or crusted scabies can occur in the elderly, people with weakened immunity or disabilities. The skin lesions appear as marked scales and crusts, which contain large number of scabies mites and eggs. The nails may thicken, with debris in the nail bed. Face and scalp can also be affected. However, persons with crusted scabies may not show the usual signs and symptoms of scabies such as rash and itchiness. This type of scabies is highly contagious because an infested person may harbour thousands of mites, compared to 10 to 15 mites in typical scabies.
Mode of transmission
Scabies usually spreads through direct skin contact with an infested person. Clothing and bedding contaminated by an infested person may also carry the mites or eggs and transmit the disease. Transmission within household and institutional settings is common.
Incubation period is about 2 to 6 weeks for people with new infestation. For people who have previously been infested with scabies, symptoms develop sooner, usually within 1 to 4 days after re-exposure. Infested people can spread scabies even if they have no symptoms.