Scabies

Scabies is a contagious skin disease caused by mites. Scabies mites are parasites that specialize in humans. That means they can only survive and multiply on human skin. The female mites burrow into the upper layer of the skin and deposit their eggs and excretions in the burrows. The body’s immune response to this causes a rash. In addition to the visible burrows and rash, scabies is typically characterized by severe itching that is often worse at night.

The word scabies is derived from the Latin word scabere, meaning “to scrape”. Scabies can be treated effectively with medication, which is usually applied to the skin in the form of creams.

It takes an average of 2 to 5 weeks after an initial infestation with scabies mites for the itchy rash to develop as an immune response. However, a person who has been infected can already infect others before the rash is noticeable. In people who have had scabies before, the rash appears after just a few days. This is because the body’s immune system recognizes the mites and therefore responds to them quicker.
 
Severe itching, which occasionally affects the entire body and becomes worse at night, is typical for scabies. The itching involves a rash that is characterized by small lumps, blisters and pustules. This itchy rash (eczema) is triggered by the immune system’s reaction to the mite infestation.
 
The mite burrows manifest themselves as fine, irregular raised areas on the skin. These are up to a centimeter long and resemble a comma with their curved shape. They cannot be easily made out with the naked eye, and the mites themselves can only be seen with a microscope or certain magnifying glasses (dermatoscope). 

The burrows are often located:

• between fingers and toes
• on ankles, wrists and elbows
• on armpits, nipples and the navel
• in the groin and buttocks
• on the penis

In rare cases, especially with babies and small children, the head (when it has grown hair), face, palms and soles can also be affected.

People with a weakened immune system often have an especially virulent form of scabies in which extensive scaly areas of redness and thick scabs develop on the skin. This is more particularly known as crusted scabies (Scabies crustosa). The otherwise so typical itching is sometimes absent in this form of the disease.

Scabies is an infectious disease that is primarily transmitted from person to person through direct skin contact. As the scabies mites move very slowly, however, continuous and extensive contact for at least 5 to 10 minutes is needed, for example when playing, cuddling or sleeping in the same bed. A simple handshake or short hugs on the other hand do not cause infection as a rule.

An exception to this rule is crusted scabies (Scabies crustosa), in which patients’ skin is colonized by thousands or even millions of parasites. In this case, brief skin contact or contact with flakes of shed skin is sometimes enough to contract the condition.

Along with the scabies mites that specialize in humans, there are other types of mites that infest pets. These mite diseases in animals are called mange.

While the animal mites occasionally migrate to humans, they die off quickly on human skin without multiplying there. The skin irritation that they sometimes cause (“pseudoscabies”) usually disappears by itself after a short time.

Scabies occurs in all age groups throughout the world. However, it is especially prevalent in children and sexually active people with changing partners. The elderly and people with restricted mobility or an immune deficiency are prone to highly contagious crusted scabies.

Scabies outbreaks can also occur in community facilities such as kindergartens, rest homes, hospitals, homeless shelters or prisons.

However, there are no verified figures about how common overall this parasite infestation is in Germany, because there is no broad obligation to notify the authorities. Despite this, scabies is one of the most widespread infectious diseases and may affect several hundred thousand people in Germany every year. This conclusion can be reached on the basis of studies such as the 2018 study by the Robert Koch Institute on the morbidity rate (the prevalence of the condition). At the same time, the morbidity rate may fluctuate from region to region over the course of many years.

Scabies mites are often transmitted to other people unnoticed before the symptoms of the disease appear. In such cases, it is hardly possible to prevent infection.

But if, on the other hand, the disease has already been discovered in a patient, close contacts should be examined and all of them treated, preferably at the same time. If physical contact with sick people cannot be avoided, for example when caring for relatives, long-sleeved clothing and disposable gloves provide protection.

To stop mites spreading via objects in a shared household, the clothes and towels of the infected person should be washed every day at a minimum temperature of 50 degrees Celsius, bed linen should be freshly changed following treatment and upholstery should be vacuumed with a powerful vacuum cleaner.

Contaminated items can also be stored in sealed plastic bags for 3 days at a minimum temperature of 21 degrees Celsius, for example close to a radiator. This kills off the scabies mites. The same applies to freezing the affected items for 2 hours at minus 25 degrees Celsius if dealing with conventional scabies and not crusted scabies (Scabies crustosa). 

People who have scabies or are suspected of having it should not visit community facilities like schools or kindergartens or work in them until the treatment has finished.

Experienced doctors can often diagnose scabies based on the typical symptoms and a physical examination. The diagnosis is confirmed by using a microscope to detect the mites in skin particle scrapings or a special kind of magnifying glass (dermatoscope) to detect them directly on the skin. Lab tests are not necessary for a scabies diagnosis.

Scabies can usually be treated with medication that is applied externally to the skin. Permethrin is usually used as the active ingredient here. Alternatively, benzyl benzoate or crotamiton can be used, for example. Taking tablets with ivermectin as the active ingredient is possible in certain cases. However, ivermectin should not be used for pregnant women or small children.

In most cases, scabies patients treated with permethrin are no longer contagious following initial thorough treatment of the entire body. To be on the safe side, however, the treatment should be repeated after a week.

After treatment, the itching subsides within 1-2 weeks.

With severe crusted scabies (Scabies crustosa), repeated treatment and more prolonged avoidance of unprotected contact with others are required.

The Robert Koch Institute (RKI) provides a great deal of further information about scabies on its website.