Scabies mites

The image shows microscopy of a scabies mite – Sarcoptes scabiei. It was extracted with a dental probe from a scabies track on a patient. Several generations of family members were infected. A total of about ten persons were treated according to the current guidelines of the Norwegian Institute of Public Health (1).

The incidence of scabies in Norway is increasing sharply, with a tripling of the number of cases diagnosed in general practice from 2012 to 2018 (2). This tendency is continuing, and has been reported from all over the country. Scabies can be seen in all age groups, but most frequently in young adults aged 15–29 (2).

The typical scabies patient is a person without any other skin disease, but with new onset, persistent intense pruritus without known cause. Scabies comes to mind when the dominant symptom is generalised pruritus, particularly when the itching is most pronounced at night. Pruritus tends to develop 3–6 weeks after infection.

In the event of re-infection, patients who have previously had scabies experience pruritus after a few days. This is probably a form of hypersensitivity reaction (1). Scabies patients will develop excoriations and papules on large portions of the body, particularly the nates, but often not on the back. Papules on the penis are frequently called pathognomonic (1). The patients are often so excoriated that scabies burrows cannot be found. Treatment with a topical group III steroid cream can then be administered for 7–10 days. This relieves the pruritus and scratching, so that the rash is reduced and the burrows become clearer. A new examination will then allow a diagnosis to be made.

Burrows are most often found on fingers, wrists, feet and ankles. They are greyish-white, about 1 mm wide and 3–15 mm long, and may be straight or curved. With a magnifying lamp it is often possible to see a dark point where the mite is located. If tracks are not found on the hands and feet, the search must be widened to the genital and perianal areas, the armpits, elbows, knees, nipples and navel. Detection of a scabies burrow provides a basis for general practice treatment. With common scabies infestation, there tend to be 10–15 mites in the skin. A rare form, crusted scabies, for historical reasons called Scabies norwegicus, has a different clinical presentation, with hyperkeratotic crusted lesions, often with limited pruritus. There are thousands of mites in the skin, it is highly contagious and requires special treatment. The condition is seen in the elderly, patients with immune system suppression and in institutions.

In a time of accelerating incidence, we need to keep both these forms of scabies in mind. The recommended treatment is detailed on the website of the Norwegian Institute of Public Health (1).