Scabies is a contagious, parasitic infestation of the skin caused by human itch mites. These microscopic parasites burrow into the superficial skin layer. The presence of the mites and their eggs causes an inflammatory reaction in the skin that manifests as an intensely itchy rash. Scabies is highly contagious and spreads almost exclusively via skin-to-skin contact with someone who has the condition. Scabies does not go away without prescription antiparasitic medication. Left untreated, a scabies infestation progresses and transmission to other people remains a persistent risk. Bacterial infection and other complications may also develop.
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Mite Infestation Progression
Scabies provokes itching and a crusty, pimple-like rash caused by an immune reaction to various human itch mite proteins. The rash develops 2 to 6 weeks after the initial infestation. If scabies is left untreated, the mites reproduce and the area of infestation enlarges and can spread to skin not previously affected. Areas commonly involved include the skin between the fingers and the skin folds of the elbows, wrists, armpits, knees, buttocks, breasts, waist and groin. Excessive scratching can cause open wounds that might result in scarring. Seniors, disabled people and those with a weakened immune system sometimes experience less severe itching but more skin crusting. This is known as crusted scabies.
Localized Bacterial Infection
Intense itchiness typically occurs with scabies, which is often worse at night. Repeated scratching can lead to breaks in the skin and a secondary bacterial skin infection, usually caused by staphylococcal or streptococcal bacteria. Areas of the scabies rash with a superimposed bacterial infection commonly demonstrate increased redness, warmth and pain. Open sores may be present and ooze pus. A fever can occur if the bacterial infection spreads to the deep skin layers or the tissues beneath the skin. People with scabies who have a superimposed bacterial infection usually require antibiotics to kill the bacteria along with antiparasitic medication to eliminate the human itch mites.
People with an untreated streptococcal infection superimposed on scabies may sustain kidney damage. This condition, known as postinfectious glomerulonephritis (PIGN), manifests as mildly impaired kidney function to full-blown kidney failure. PIGN occurs due to inflammation of small blood vessels in the kidneys. Signs and symptoms of severe PIGN include bloody or brown urine, decreased urination, high blood pressure, swelling of the hands, feet, lower legs and face, and possibly fever.
Additionally, a localized bacterial skin infection superimposed on scabies can spread to the bloodstream. This condition, known as septicemia, can be extremely dangerous and difficult to treat once it reaches an advanced stage. Life-threatening shock might occur with multiple organ system failure, which can be fatal. Signs and symptoms include fever, rapid heart and breathing rate, sweating, falling blood pressure, and decreased alertness or confusion.
Tansmission to Others
Adults and children with untreated scabies can spread the condition to others. People who live in the same home and sexual partners are most likely to contract scabies from someone with the infestation. People with crusted scabies are more contagious than those with ordinary scabies because their skin can be infested with up to 2 million live mites.
Most cases of scabies occur due to skin-to-skin contact with someone with the condition. However, adult female itch mites can survive for up to 2 to 3 days outside the human body in hot, humid conditions. In tropical environments, therefore, furniture, towels, sheets and clothes contaminated with living human itch mites can potentially lead to transmission to others.
Warnings and Precautions
See your doctor as soon as possible if you suspect you or your child might have scabies. Prescription medication is needed to eradicate the infestation. No over-the-counter or home remedies have been proven effective.
Seek urgent medical care if you develop signs or symptoms of a secondary bacterial infection. If any signs or symptoms of kidney failure or sepsis develop, seek emergency medical care.
Reviewed and revised by: Tina M. St. John, M.D.
- Centers for Disease Control and Prevention: Parasites -- Scabies
- Merck Manual Professional Version: Cellulitis
- Clinical Microbiology and Infection: Scabies in the Developing World -- Its Prevalence, Complications, and Management
- Clinical Infectious Diseases: Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America
- Merck Manual Professional Version: Postinfectious Glomerulonephritis
- Merck Manual Professional Version: Sepsis and Septic Shock