Symptoms
Scabies is a parasitic skin disease caused by mites that burrow into the skin and multiply. The primary lesion is found to be a comma-shaped reddish duct up to one centimeter long, at the end of which the mite is visible as a black dot. Due to an allergic reaction to the type IV mites, the so-called scabies exanthema with redness, papules, vesicles and crusting develops three to four weeks after the initial infestation. Typical is the strong and unpleasant itching, which worsens in the warmth of the bed, because heat lowers the threshold for itching. Scratching further aggravates the rash. Scabies occurs mainly on warm skin areas between the fingers and toes, on the wrist, ankle, genital area, buttocks, breasts, elbows, armpits, and navel. The head is usually left out, but in infants the face and the soles of the hands and feet are also affected.
Cause
The trigger of the disease is the scabies mite var , which is between 0.2 to 0.5 mm in size and belongs to the class of arachnids. The mites cannot fly or jump but can crawl relatively quickly on the skin (2.5 cm per minute). Their life cycle begins with the fertilization of the female on the skin surface. During this process, the males die. Only the female burrows into the stratum corneum of the skin, where she survives between 30 and 60 days, laying 2 to 4 eggs daily. The eggs develop into larvae within a few days, which work their way back to the surface of the skin, where they mature into sexually active mites over various stages for a maximum of two weeks. In normal immune status, only about 5 to 15 burrowed mites are found on the skin at any one time.
Transmission
Once on the skin, mites can burrow within minutes. They are mainly transmitted from person to person through close and prolonged (possibly repeated) skin contact, for example, during cuddling, sexual intercourse, breastfeeding, or nursing (nursing homes). Scabies is therefore also counted among the sexually transmitted diseases. A handshake or a short hug is not enough. Transmission via objects, clothing and bedding is possible, but is considered rare. This is because the mites have a limited viability outside the body and die after only 24 to 36 hours. Immunocompromised individuals with scabies norvegica (see under Complications) are highly contagious and can lead to greater spread in a group.
Complications
The body’s immune response restricts infestation and, in some cases, prevents reinfection. If this response fails to occur in immunosuppressed individuals, a massive multiplication with millions of mites can occur (scabies norvegica). Other complications include skin damage and secondary bacterial infections.
Risk factors
- Poor hygienic conditions
- Poverty, overpopulation
- Close physical contact with other people
- Retirement and nursing homes
- Immunosuppression
- Cool season
Diagnosis
Some clues can already be obtained from the medical history (nocturnal itching, itchy skin disease, simultaneous infestation of family members). The clinical picture also provides clues, but the mite ducts are often no longer easily recognizable due to the skin rash. Due to the small size of the mites, the tissue is examined by light and dermatoscopy. Numerous skin diseases come into question as differential diagnoses and must be excluded in medical treatment. Crabs can cause a similar picture in the genital area. However, crabs do not live in the skin but in the pubic hair.
Non-drug treatment
Scratching may remove the mites mechanically, but at the same time it may make the skin condition worse. Without medication, it may take years for all pathogens to be eliminated by the immune system or by scratching.
Drug treatment
So-called antiscabiosa, i.e. agents effective against scabies mites, are used for drug treatment of scabies. The instructions in the corresponding package inserts should be followed exactly. Generally, the agent is spread over the entire body from the lower jaw downwards and left to take effect overnight. It is best to have a partner or family member help, otherwise not all areas will be reached.For some drugs, a single application is sufficient, others are applied every evening for 3 to a maximum of 5 days. After 10-14 days, the treatment can be repeated if a persistent infestation is suspected. Close contacts should be treated if possible, even if no infestation has been detected. It should be noted that skin afflictions and itching may persist for weeks to months after successful treatment. This is not due to treatment failure. Permethrin (Scabi-med) is considered the agent of choice according to the literature. The cream is applied to dry skin in the evening and left to act overnight for at least 8 hours. As a rule, a single treatment is sufficient. The application can be repeated after one to two weeks. See under permethrin cream. Benzyl benzoate is a possible alternative to permethrin and is approved in Germany. The emulsion is applied to the entire body from the neck down for three consecutive days and not washed off until the 4th day. It is also not available in many countries. In Germany, it is available under the brand name Antiscabiosum (10% or 25%). Crotamiton (Eurax) is reported to be additionally effective against itching and bacteria and was approved for treatment in adults in many countries. The entire skin surface (excluding face and scalp) is rubbed in the evening. The duration of treatment is 3-5 days. According to some sources, it is significantly less effective than permethrin. Eurax has been off the market in many countries since 2012. Ivermectin is administered internally as a single dose and is another possible treatment alternative. It is used, for example, in highly contagious Scabies norvegica, where there is a large-scale infestation. Ivermectin is not approved as a human drug in many countries and must be imported from abroad (Stromectol, e.g. from France). Treatment of skin afflictions includes the use of anti-inflammatory topical glucocorticoids and, for secondary infections, antibiotics. Various agents are available for itching (see under the article Itching). Other options: Allethrin, mesulfen, sulfur (10% in petroleum jelly), Peru balsam, and tea tree oil are effective against scabies but are not among the first- or second-choice remedies. Other treatments (including herbal) are conceivable but have been insufficiently studied. Lindane (Jacutin) is out of commerce and should no longer be used because of the potential adverse effects. Malathion (Prioderm) is also no longer available in many countries.
