Classical scabies is a parasitic infection that is caused by the presence of mites on the skin. The microscopic human itch mites burrow shallow tunnels into the upper layer of the skin.1 The human itch mite is an eight-legged bug that is less that 1mm large, and is nearly impossible to view without a microscope.3 The mites then live and lay eggs in those burrows. An infected person will experience itching and a rash to the affected area. Scabies is transmitted via prolonged skin-to-skin contact with someone who has the infection. The infection can spread quickly under crowded conditions. Sites with lots of people in a small space, such as nursing homes, childcare centers, and prisons, are more susceptible to outbreaks because of the close personal conditions.1

Norwegian (Crusty) Scabies

Norwegian scabies is a form of scabies that is transmitted much more easily because of the greater number of mites found in the skin, as opposed to the 10 to 15 that are found on a regularly infected person. It is the result of a weakened immune system that allows for hundreds of scabies mites to burrow, live, and reproduce in the upper layer of the skin. It is much more common among the elderly, people with acquired immunodeficiency syndrome (AIDS), cancer, or any autoimmune disorder. Symptoms of Norwegian scabies are more severe than classical scabies and can develop sites that can be predisposed to secondary bacterial infections. Just like scabies, Norwegian scabies can be treated with a topical lotion and an oral medication, as prescribed by a physician.2

Symptoms

A person with scabies may not exhibit any symptoms for 4 to 6 weeks, but can still transmit the infection to other people during this asymptomatic period. Some symptoms include itching, especially at night, and a papular rash. A papular rash is composed of small, raised bumps on the skin.1 The itching itself is not painful, but rather irritating and relentless, similar to that of a mosquito bite. It generally is not incessant enough to prevent sleep or wake people up in the middle of the night.2 Common sites of infection are at the wrists, elbows, and armpits, in between the fingers, nipples, penis, waistline, and buttocks. In order to prevent another infection, it is important to try not to scratch the rash, as it can develop sores that are open to bacteria and can lead to infection. The burrows may be difficult to find because they are so small and narrow. However, they can be identified as narrow, raised, white or grey lines on the skin.1 Continuous itching of the affected areas may lead to a secondary skin infection because of the constant irritation. It is estimated that there are about 300 million cases of scabies a year throughout the world and is more common in nursing facilities, hospitals, and other care institutions.2

Transmission and Cause

Generally, scabies is spread to others via prolonged skin-to-skin or fabric-to-skin contact with someone who already has scabies. This prolonged exposure can include sexual interactions with partners, as well as indirectly sharing clothing or bedding.1 A simple handshake is not enough skin-to-skin contact for scabies to transfer from one person to another.2 Scabies cannot be spread from an animal to a human because mites on animals cannot survive on human skin. Animals can become infected with another kind of mite, and produce an infection that does need to be treated under a veterinarian’s care. Although scabies can be spread from fabric, the mites cannot survive more than a couple of days away from human skin. However, it is recommended to thoroughly clean any potentially infected towels, clothing, and especially bedding in hot water. Dry cleaning is also recommended.1 Because sexual contact is the most common form of transmission, scabies is often classified as a sexually transmitted infection (STI).2

Diagnosis and Treatment

Scabies can be easily diagnosed from the visible burrows on the skin in conjunction with a rash to the affected area. Doctors may also use a microscope to check the skin for mites, eggs, or mite fecal matter. However, a person can be infected with scabies even if there is no evidence of mites, eggs, or mite fecal matter. Scabicides are used to directly kill scabies mites and eggs, but are only available with a doctor’s prescription. This scabicide cream or lotion is applied to the entire body, not just the physically affected area, in order to cover any area that may be infected but may not show symptoms yet. It is also recommended that other people in the household adhere to the same treatment, in order to treat any asymptomatic infection and prevent a further outbreak. Itching should cease two to four weeks after the initial application, although it may be necessary to reapply if symptoms persist.1

Concluding Remarks

Scabies is a parasitic infection caused by human mites that burrow under or into the upper layer of the skin. It is treatable and curable with topical and oral medications, after a doctor’s consultation. Since scabies is highly contagious, it is recommended to abstain from any prolonged physical contact with anyone that may exhibit symptoms of scabies.

References

1. “FAQs of Scabies,” 2018, Center for Disease Control.
2. Melissa Conrad, Stoppler, “Scabies,” 2017, WebMD.
3. “Scabies,” 2018, American Academy of Dermatology.

Last Updated: 17 April 2018.