scabies

Scabies is an itchy infestation of the skin with an incredibly tiny little bug, the scabies mite. It can't be seen without a microscope. It burrows in the top dead layer of the skin, eating the dead skin cell debris. Its fecal material provokes an allergic reaction that causes intense itching. In bygone days, when there was no effective treatment, scabies was called seven year itch - for obvious reasons. It is spread by close human contact, just like head lice - direct person-to-person, or by vectors such as clothing or bedding.

Diagnosis is by typical appearance and history of exposure. Sometimes it's necessary to scrape the little sores with the flat side of a scalpel blade (it doesn't hurt) to pop out the little bugs in a droplet of oil for the doctor to examine under the microscope.

Treatment used to be the application of 1% lindane, an insecticide (tradename Kwell®). Ordinarily it seemed harmless enough, but if applied in excess amounts repeatedly to small children, enough of the chemical got in the bloodstream to cause brain damage, leading to the usual large lawsuits. Thus it has been used less and less by pediatricians any more, although I am told it still can be used very safely if used prudently. Now we use topical permethrin 0.5% cream (Elimite®) which is a chemical analog of naturally occurring plant defenses against bugs. It must be left on overnight - 8-12 hours - to work, and should be repeated in one week. Crotamiton (Eurax®) has a failure rate of greater than 50% and is no longer recommended.

Follow the directions exactly, and realise that the itching isn't going to go right away, even though the bugs are dead. Cover the whole body from the neck down - the bumps are where the critter was, not where he is now. The little itchy sores will get gradually better and should be gone in 10-14 days, with no new sores appearing after treatment.

It is possible that a rash consisting of little pustules or vesicles will appear on the hands and feet about two to three weeks following successful treatment of scabies. This is an allergic reaction to the dead scabies mites and responds well to steroid cream. It does not require re-treatment.

Scabies can infest very small infants as well as older toddlers, children and adults. When it affects very young infants, the rash can be confusing to the doctor because it often involves the face (not usually seen in older children), involves the palms and soles with untypical blistery-looking lesions, and generally does not look quite like the classic rash on an older child. If your baby has a weird rash that is stumping the doctor and someone around the baby has had scabies (or it's in the day care center) be sure to mention that.

When we treat infants and children less than two years old, it is necessary to apply the medicine even to the face (avoiding the eyes). The medicine should even be rubbed under the child's fingernails. Failure to cover the neck, scalp and face is a common reason treatments may not work.

Scabies sores may become infected, often with Staph. germs, and this infection will of course need to be treated as well. A clue to this type of infection is larger, redder pus-containing sores.

Eradication of the mite in your household will involve treating the whole family properly and some simple hygeine measures. Launder all bedclothes and personal garments the family has worn in the 48 hours before treatment. You do not have to spray everything in the house with scabicides - the mite survives very poorly away from human skin.

In summary: failure to eradicate the infestation usually means

it isn't actually scabies
you did not cover the whole body: head to toe, including scalp, behind the ears, under the nails and in all folds and creases
you did not treat everybody in the household
it was scabies, but now it is post-scabies eczema; this condition can itch for 2-4 weeks after successful treatment of the scabies
you used Eurax®

One condition that can be confused with infant scabies is acropustulosis of infancy - worth knowing if your child has apparent infant scabies of the hands and feet that does not clear with treatment.

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