Scabies is a parasitic infection, although it does not feel this way perhaps to the patient.
It is caused by a mite, called Sarcoptes scabei, which has the nasty habit to create mini tunnels underneath the skin surface, called burrows. Eggs are deposited there and within a few days larvae are hatched and the cycle begins anew. The body reacts to the foreign protein with an inflammatory skin papule, which is very itchy.
These typical scabies lesions throughout the body and the burrows that look like fine lines may be a bit scaly, would be up to 1 cm (1/3 inch) long and are the hallmarks for the clinical diagnosis.
Distribution of scabies lesions
Here is a scabies picture regarding scabies lesions in the web between the base of two adjacent fingers and on the volar aspect of the wrist (typical locations). On close inspection you can see a burrow with inflammation around it.
These burrows are found mainly in the soft skin of the flexor side of the wrists, finger webs, in the pigmented soft skin of female breasts, in male genital skin, in the elbows and the arm pits. The skin in the area of the belt line and in the lower buttock region is also frequently infested. The dermatologist can take scrapings and examine the sample under the microscope. The appearance of the mite under the microscope in the lab, the shape and size of the ova and the fecal pellets of the mites are the signs, which lead to the specific diagnosis.
Adults and children alike tolerate topical treatment with permethrin (brand name: Kwellada or Nix). This is therefore the treatment of choice. It is applied from head to toes with particular attention to skin creases, finger webs, perianal regions, genitalia as well as toe webs. It should stay on for 12 to 24 hours. This will very quickly kill the mites. However, the dead mites in the skin are still allergenic and the allergic rash and skin itch can still last for 1 or 2 more weeks. The physician treats this with topical fluorinated corticosteroid creams.
More severe scabies cases
In severe scabies cases with a lot of itchy papules the patient may have to take oral prednisone for 7 to 10 days to help cope with the itch. However, the side effects of the systemic corticosteroids can by themselves be devastating (avascular necrosis of hips etc.). On the other hand, topical corticosteroids are quite safe. In the past physicians recommended Lindane cream or shampoo, but children are very sensitive (seizures, neurotoxicity, also skin irritant), which precludes use of this medication in children. Now physicians use it only rarely in adults. Sulfur medications are now also obsolete (Ref. 4, p. 806 and Ref. 2, p. 445).
1.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 265.
2.James Chin et al., Editors: Control of Communicable Diseases Manual, 17th edition, 2000, American Public Health Association
3.The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 112.
4. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 115.
5. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 113.