The scab is a disease of contagious skin caused by a mite, mite. It causes itching of nocturnal predominance that is sometimes very intense and insomniating, especially in the hands, underarms, belly and genital area.
It is a benign parasitosis in the vast majority of cases, but requires treatment because it does not heal spontaneously.
Contrary to popular belief, scabies is not caused by a lack of hygiene and can be rife in all social circles.
Causes of scabies
Scabies is caused by colonization of the skin by a mite, Sarcoptes scabiei hominis, which is about 0.4 mm in size and is difficult to see with the naked eye. The female digs a furrow under the skin and lays its eggs there. Three to four days after spawning, the larvae hatch and migrate to the surface of the skin where they dig a new furrow called the “scabious furrow”, whose presence usually confirms the diagnosis. An infected person “hosts” on his skin about 5 to 10 mites.
The resulting itching is the result of an immune system response to the presence of the parasite and its eggs and excrement under the skin. They usually occur three weeks after the infestation, but much more quickly (a few days) in case of a second infection, because the body is then “hypersensitive” to the parasite.
Scabies is a very contagious condition: transmission is mainly by direct contact, skin against skin. It is favored by close and prolonged physical contact: family life, groups of children, community life. Scabies can also be sexually transmitted.
In some cases, indirect transmission from linen or bedding is possible, even if the parasite does not survive long outside the human skin.
Evolution and possible complications
Scabies is not a dangerous disease, but persistent and intense itching can strongly affect the quality of life. The lesions can sometimes become infected because of scraping, or evolve, in rare cases, in scabies called “crusted” or hyperkeratotic
The symptoms of scabies
The main symptom of scabies is diffuse pruritus, which is diffuse itching, which worsens at night and can disturb sleep. Pruritus is predominantly nocturnal. Itching often affects many family members (family pruritus), several schoolchildren or those around them at the same time.
Itching and lesions occur mainly at:
- interdigital spaces (between the fingers)
- breasts in women
- genitals in men especially
- belly around the navel
The most characteristic skin lesion of scabies is the scabious furrow (small red furrow, not always easy to spot, predominant on the hands and wrists), but other types of lesions may also be present (small button type, nodule, etc.).
Generally, the doctor does not need to make an examination to diagnose scabies, but sometimes he can take a skin sample or a dermatological examination (dermoscopy) to visualize the parasite under a microscope.
Scabies can be confused with other skin conditions, including atopic dermatitis, lichen planes, eczema.
The different types of scabies
Apart from common scab, there are several types of scabies among which can be mentioned:
Crusted scabies formerly called “Norwegian”
It is a form most often found in the elderly, bedridden, immunocompromised (corticosteroid, HIV …), cachectic … It is misleading because it is in the form of profuse crusts, it itches little or no and it is extremely contagious because the patient is infected with thousands or even millions of parasites. In these debilitated individuals, scratch-related lesions can also promote life-threatening bacterial infections (sepsis).
Scabies of “clean people”
It is a common form in adults with impeccable hygiene, characterized by the presence of itching accompanied by little injury. The doctor mentions scabies in the presence of an eczema-resistant eruption resistant to topical corticosteroids, often after several weeks of diagnostic wandering, or even in the presence of scabious scrotal nodules, or itching of the surrounding area.
Scabies of infants and young children
The lesion is usually only palmoplantar characterized by vesiculo-pustules (small water blisters on the hands and feet, with clear or purulent contents). Scabies of infants and young children evolve in generalizing, often resembling a prurigo or a profuse eczema, one sometimes notes an attack of the back, the face or the scalp, much more frequent than in the adult, scabious nodules , an irritable and tired child, lacking sleep.
Differences with other skin diseases
Scabies can be confused with other skin conditions, including atopic dermatitis, lichen planus, eczema …: the diagnosis of scabies is sometimes difficult; here are some benchmarks to distinguish it from other diseases of skin
Atopic dermatitis of the child, eczema, prurigos: presence of a dryness of skin, absence of itching with predominantly nocturnal,
Lichen planus: presence of purplish papules prevailing on the wrists, white patches on the inside of the cheeks, no itching at night and pruritus,
Coetaneous lymphoma: fatigue, deterioration of general condition, plaques not typical of scabies, presence of ganglia, absence of itching at night and pruritus of the family,
Body lice: poor social context (SDF …), no itching at night
Insect bites: predominant lesion of folds or open areas, no predominantly nocturnal itching
Medication rash: concept of taking a new drug or switching to a generic drug in the days or weeks before the rash, profuse patches on the entire body, no itching at night and family pruritus
People at risk for Scabies
Everyone can be affected by scabies, but some people are more fragile, including:
- young children (in some countries, 5 to 10% of children are affected source ),
- old people,
- people with HIV / AIDS,
- People whose immune system is weakened (immunosuppressive treatment, leukemia, transplant recipients, etc.).
These people are also more likely to suffer from Norwegian scabies.
Several factors can promote the transmission of scabies:
- promiscuity (schools, daycares, hospitals, retirement homes …),
- the lack of treatment of the first affected individuals or all affected contacts,
- reduced access to care and clean water,
- The absence of eradication of scabies on clothes and bed sheets.
Prevention of scabies
|Can we prevent?|
|It is not possible to prevent infection by parasites when in close contact (sleeping in the same bed, having sex, exchanging clothes …) with people with the disease. Only rapid care of affected people can help limit parasite transmission.|
|Basic preventive measures|
|Once a case of scabies appears, the following measures must be applied:
Medical treatments for scabies
Treatment recommendations for scabies vary by country. In addition, the recommended drugs in some countries are not marketed everywhere.
However, all the treatment recommendations agree on the following points:
- Treatment is either oral or local, as studies fail to determine which of these modalities is most effective.
- The treatment must be put in place quickly, and the contacts of the affected person must also be treated (depending on the proximity to the case and the type of mange).
- The laundry must be disinfected to avoid possible recontamination.
Note: itching may persist for one to two weeks after treatment.
In France, faced with the recrudescence of cases of scabies, the High Council of Public Health (HCSP) has made new recommendations in 2012 that are inspired by other international recommendations. In spite of a “low level of evidence”, the High Council recommends proceeding with “two applications for topical treatments (local) or two oral administrations for ivermectin”. This precaution eliminates all parasites that could have “escaped” the first treatment and larvae hatched in the meantime.
Oral treatment with ivermectin
This is the only treatment against scabies refunded by the Health Insurance in France. In addition, its simplicity of administration tipped the balance in its favor in case of epidemic. Ivermectin acts by neutralizing the nervous system of parasites, with varying efficacy depending on the studies. It is given as a single oral dose and is well tolerated, even if it sometimes causes dizziness and lightheadedness.
A second dose may be offered two weeks after the initial dose.
Ivermectin is also indicated for the treatment of Norwegian scabies or hyperkeratosis at doses of 200 μg / kg. It can be used in immunocompromised people, but not in pregnant women or young children.
In case of hyperkeratotic mange, the HCSP recommends that the patient be hospitalized in strict isolation, dermatological environment. “A double treatment, general and local, are essential, and must be repeated weekly until the parasitological samples are negative”.
Local treatment (topical)
Two local treatments for scabies are available in France:
- Benzyl benzoate / sulfiram, which seems to be the preferred local treatment, although its effectiveness in single application does not exceed 60%.
- Esdepallethrin (synthetic pyrethroid) spray.
- Permethrin at 5%.
- Lindane lotions, effective but toxic, are generally no longer used, at least in developed countries.
Hygiene measures to prevent the spread of scabies
The laundry (clothes, bed linen, towels) used for less than a week must be washed at 60 ° C (this is sufficient to decontaminate).
According to the recommendations of the HCSP, in the case where the laundry cannot be machine washed at this temperature, the use of an acaricide product is recommended.
The laundry should be left in contact with the acaricide in a bag for at least 72 hours at room temperature.
Environmental treatment (house, furniture, etc.) is not necessary in case of common scab. It is however essential in case of hyperkeratotic or crusted scab.
According to the World Health Organization, scabies affects about 300 million people every year, especially in poor countries where it can affect 50% of the population during epidemics. But it can affect people of both sexes, of all ages, including infants, and all walks of life.
In industrialized countries, scabies occurs mainly in communities (schools, crèches, prisons, health facilities) or long-stay institutions, especially for the elderly .
From 2008 to 2010, the French Institute for Public Health Surveillance conducted an epidemiological study which concluded that the number of cases has increased . In early 2013, several epidemics were reported in France, particularly in Burgundy and Charente. According to the High Council for Public Health (HCSP), there would be at least 328 annual cases per 100,000 inhabitants, and the estimated incidence of scabies in France has increased by 10% since 2002, as in the other western countries .