La scabies is a contagious skin condition caused by a dust mite, the sarcopte. It leads to itching predominantly nocturnal sometimes very intense and sleepless, especially in the hands, armpits, stomach and genital area.

It’s about a parasitose benign in the vast majority of cases, but which requires treatment because it does not heal spontaneously.

Contrary to popular belief, scabies is not caused by a lack of hygiene and it can be rampant in all social settings.

Causes of scabies

Scabies are caused by the colonization of the skin by a mite, Sarcoptes scabiei man, which measures approximately 0,4mm and is difficult to see with the naked eye. The female digs a furrow under the skin and lays her eggs there. Three to four days after laying the eggs, the larvae hatch and migrate to the surface of the skin where they make a new groove called the ” scabious groove », The presence of which generally confirms the diagnosis. An infected person “lodges” on their 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 feces under the skin. They generally occur three weeks after the infestation, but much more quickly (a few days) in the event of a second infection, because the organism is then “hypersensitive” to the parasite.

Scabies is a very contagious : transmission occurs mainly through direct skin-to-skin contact. It is favored by close and prolonged physical contact: family life, groups of children, community life³. Scabies is also sexually transmitted.

In some cases, indirect transmission from linen or bedding is possible, although the parasite does not survive for long outside human skin.

Course and possible complications

Scabies is not a dangerous disease, but the persistent and intense itching can strongly affect the quality of life. The lesions can sometimes become infected due to scratching, or develop, in rare cases, into so-called “crusty” or hyperkeratotic scabies.

Symptoms of scabies

The main symptom of scabies is a diffuse pruritus, that is to say diffuse itching, which gets worse at night and can disrupt sleep. We are talking about predominantly nocturnal pruritus. Itching often affects at the same time several family members (familial pruritus), several children of the school or people of the entourage.

Itching and lesions occur mainly at:

• interdigital spaces (between the fingers)
• wrists
• armpits
• breasts in women
• genitals in men especially
• belly around the navel

The most characteristic skin lesion of scabies is the scabious groove (small red groove, not always easy to spot, predominantly on the hands and wrists), but other types of lesions may also be present (such as a small button, nodule, etc.).

Usually, the doctor does not need to do an exam to diagnose scabies, but sometimes they can take a skin sample or do a skin test (dermoscopy) to view the parasite under a microscope.

Scabies can be confused with other skin conditions including atopic dermatitis, lichen planus, eczema.

The different types of scabies

Apart from common scabies, there are several types of scabies, among which we can cite:

Crusted scab formerly called “Norwegian”

It is a form most often encountered in the elderly, bedridden, immunocompromised (corticosteroid therapy, HIV, etc.), cachectic, etc. It is misleading because it appears in the form of profuse scabs, it itches little or not and it is extremely contagious because the patient is infected with thousands or even millions of parasites. In these debilitated people, scratching lesions can also promote life-threatening bacterial infections (sepsis) 4.

Gale of “clean people”

It is a common form in adults with impeccable hygiene, characterized by the presence of itching accompanied by few lesions. The doctor mentions scabies in front of an eczema rash resistant to topical corticosteroids, often after several weeks of diagnostic wandering, or even in front of the presence of scrotal scabious nodules, or itching of the environment

Infant and young child scabies

The involvement is most often only palmoplantar characterized by vesiculo-pustules (small blisters of water on the hands and feet, with clear or purulent contents). Scabies in infants and young children progresses by becoming generalized, often resembling prurigo or profuse eczema, sometimes there is involvement of the back, face or scalp, much more common than in adults, scabious nodules , an irritable and tired child, lacking sleep. 

People at risk

Anyone can be affected by scabies, but some people are more susceptible, especially6 :

• young children (in some countries, 5 to 10% of children are affected)4),     
• seniors,
• people with HIV / AIDS,
• people with a weakened immune system (immunosuppressive treatment, leukemia, transplant recipients, etc.).

These people are also more likely to suffer from scabies Norwegian7.

Risk factors

Several factors can promote the transmission of scabies:

• promiscuity (schools, daycares, hospitals, retirement homes, etc.),
• the absence of treatment of the first persons affected or of all affected contacts,
• reduced access to healthcare and drinking water,
• lack of eradication of scabies on clothing and bed sheets.

Prevention of scabies

Medical treatments for scabies

The recommendations of scabies treatment vary by country. In addition, the drugs recommended in some countries are not marketed everywhere.

However, all treatment recommendations agree on the following points:

• The treatment is done either orally or by local route, the studies not making it possible to determine which of these modalities is the most effective.
• Treatment should be started quickly, and contacts of the affected person should also be treated (depending on the proximity to the case and the type of scabies).
• The laundry must be disinfected to avoid possible recontamination.

In France, faced with the resurgence of cases of scabies, the High Council of Public Health (HCSP) established new recommendations in 20123 which are inspired by other international recommendations. Despite a “low level of evidence”, the High Council recommends to carry out “two applications for topical treatments (= local) or to make two oral administrations for ivermectin”. This precaution eliminates all the parasites which could have “escaped” during the first treatment and the larvae which would have hatched in the meantime.

Oral treatment with ivermectin

This is the only treatment against scabies reimbursed by the Health Insurance in France. In addition, its ease of administration tilts the balance in its favor in the event of an epidemic. Ivermectin acts by neutralizing the nervous system of parasites, with variable effectiveness according to the studies. It is taken as a single oral dose and is well tolerated, although 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 or hyperkeratotic scabies, at doses of 200 μg / kg. It can be used in people who are immunocompromised, but not in pregnant women or young children.

If you have a gale hyperkératosique, the HCSP recommends that the patient be hospitalized in strict isolation, in a dermatological environment. “A double treatment, general and local, is essential, and must be repeated every week 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 efficacy in a single application does not exceed 60%.
• esdepallethrin (synthetic pyrethroid) spray.
• 5% permethrin.
• Lindane lotions, effective but toxic, are generally no longer used, at least in developed countries.

Hygiene measures to prevent the spread of scabies

Linen (clothes, bed linen, towels) used for less than a week must be washed at 60 ° C (this is sufficient to decontaminate it).

According to the recommendations of the HCSP, in the event that 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 the case of common scab. However, it is essential in cases of hyperkeratotic or crusted scabies.