Last Updated: September 11, 2017

Scabies

Overview

Scabies is a fully treatable skin rash caused by the microscopic human mite Sarcoptes scabiei. It is transmitted by direct skin-to-skin contact or by contact with infested clothing and bedding. The mites burrow into the upper skin layer (epidermis) to live and lay eggs, causing raised itchy bumps along the way.

Sarcoptes scabiei mite (source: Alan R Walker)

The elderly and those with a weakened immune system may develop a severe form of scabies called crusted scabies, also called Norwegian scabies. Crusted scabies is highly contagious because of thick brittle crusts that form on the skin, each carrying hundreds to thousands of mites and eggs.

Mites are species-specific, which means mites that infect other animals cannot infect humans, and vice versa. Other species of mites may cause a minor skin reaction in humans, but they cannot reproduce.

Human scabies is very common worldwide and can affect anyone regardless of age, gender, race and ethnicity. It spreads easily in places where there is close human-to-human contact, such as hospitals, childcare centers, prisons and nursing homes. Scabies is fully treatable using medicated creams/lotions. The most common complication associated with scabies is infection of open sores due to excessive itching.

Causes and Risk Factors

Human scabies is caused by the mite Sarcoptes scabiei. Pregnant females burrow into the upper epidermis, where they lay their eggs and remain for future reproductive cycles. New mites develop and mate under the skin, then travel to the surface where they can infect a new host. In a typical infection, there are fewer than 20 mites per person and they are typically found on the hands, wrists, knees, penis, breasts and shoulder blades. The itchy skin rash that develops is caused by an allergic reaction to mite proteins, eggs and feces.

Transmission primarily takes places during prolonged, direct skin-to-skin contact (e.g. sexual contact) with an infected person. Hospitals, nursing homes and other extended care facilities are especially prone to a mite infestation. A less common means of transmission is through contact with infested clothing or linens. Crusted scabies is the most contagious form of scabies because of thick crusts on the skin that can carry thousands of mites and mite eggs. These crusts can also shelter and nourish mites for up to a week when they shed. Risk factors for acquiring scabies are:

Risk factors for crusted scabies are:

Symptoms

The most common symptoms of scabies are severe inching and body rash, which are caused by an allergic reaction to the mites. Those infected for the first time may not develop symptoms for up to two months; however, they are still contagious and able to transmit scabies. Repeat infection can produce symptoms within days. The symptoms of scabies are:

Scabies can affect any area of the body, but mites favor the following sites:

The most common areas of infestation in young children and infants are:

Diagnosis and Treatment

Doctors diagnose scabies by examining the skin for evidence of mites and/or mite burrows. The burrows are hard to find and appear as tiny greyish or skin-colored raised lines on the skin. Scrapings from the affected skin can also be studied under a microscope to find mites or eggs.

The goal of treating scabies is to alleviate the symptoms and eliminate the parasite. Since scabies is very contagious, doctors usually recommend treatment for anyone living with the infected person, as well as recent sexual partners. Scabies is treated with prescription medications (called scabicides) that kill mites and mite eggs. In most cases adults and children can resume normal activity the day following treatment, although the itch can persist for a few more weeks. If itching and rash reappear after four weeks, retreatment is needed. Treatment for scabies includes:

Prevention

Repeat infestation or a scabies outbreak can be prevented by avoiding contact with an infected person and laundering all contaminated linens and clothing in hot water. Items that cannot be washed can be sealed in a bag for 2-3 days to starve the mites.

Sources

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Authored by: Tina Shahian, PhD