Scabies: Itchy global scourge is often misdiagnosed

Most people expect to return from vacation with fond memories of a relaxing or exciting time and perhaps photos to document it. That wasn't exactly the case for one 25-year-old man who took a trip to a Brazilian beach. Five weeks after returning to his home in Spain, he began to itch. He itched everywhere, intensely, and especially at night, which made sleep almost impossible.

After two months of this torment, with pimples and the sores from scratching them on his abdomen, buttocks and genitals, he sought help from a dermatologist. The diagnosis was scabies, an infestation of tiny mites he had most likely contracted from a sexual encounter during his vacation.

In describing this case in the July issue of the Cleveland Clinic Journal of Medicine, Dr. Sergio Vañó-Galván and Dr. Paula Moreno-Martin of Madrid called medical attention to a worldwide public health problem that each year affects more than 300 million people.

Scabies is frequently misdiagnosed and mistreated, partly because most physicians are unfamiliar with it and partly because its symptoms mimic so many other skin diseases.

A correct diagnosis is further complicated by the fact that symptoms can often appear six to eight weeks after a person becomes infested with the microscopic arthropod, making it seem as if the problem came from nowhere. But unlike other skin diseases, scabies is usually accompanied by a tell-tale sign: one or more burrows in the skin where female mites lay their eggs.

Scabies is easily cured, but only if patients and their close contacts conscientiously follow directions for medical treatment and environmental cleanup. However, even after a person is rid of the mites and their eggs, itching can persist for up to four weeks.

The scabies mite, Sarcoptes scabiei, can afflict a number of animals. In dogs and sheep, the infestation is commonly called mange.

Each species of animal has a specific variant of the mite, which cannot reproduce in other hosts. If your dog gets mange, as mine once did, you may be itchy for a while if the mites get into your skin, but the condition will cure itself when the adult mites die.

It's not so easy if you acquire the human scabies mite. At 0.4 millimeter in length, the mite is barely visible to the naked eye. But just 10 adult females breeding in a person's skin are enough to cause bodywide torment, as they defecate and lay eggs that then hatch into larvae and develop into more adult mites. The itching is due to an allergic reaction to the mite, its excrement and burrows, though an antihistamine alone is rarely enough to squelch the desire to scratch.

Scratching, however, can cause sores that become infected with bacteria like staphylococci or streptococci, prompting a diagnosis of impetigo and perhaps missing the underlying cause.

Scabies spreads most often through direct, prolonged skin-to-skin contact, like that between sexual partners and members of a household.

As the U.S. Centers for Disease Control and Prevention put it in a fact sheet on scabies, "A quick handshake or hug will usually not spread infestation." But the mite can also be acquired from contaminated bedding, clothing or towels recently used by a person with scabies.

Although an adult female mite can live on a person for up to a month, the mite rarely survives more than three days apart from a living body.

According to the American Academy of Dermatology, scabies has become a common problem among elderly people living in nursing homes and extended care facilities, where it can spread easily to attendants who in turn spread it to other residents. In the elderly, scabies is often mistaken for senile pruritus, itching caused by degenerative changes in aging skin.

Although taking a shower or bath soon after contact with live mites can wash them away, an attack of scabies is not a symptom of poor hygiene. Literally anyone can get it, regardless of age, sex or social class. The mites can neither fly nor jump but rather crawl at a rate of 2.5 centimeters a minute on warm skin, Dr. Olivier Chosidow of the Université Pierre et Marie Curie in Paris reported in The New England Journal of Medicine in April 2006.

When a doctor is familiar with scabies, as most dermatologists should be, the diagnosis is relatively simple. The scabies mite has favored sites in which it lives, generally areas on the body that are warm or where clothing is tight: between fingers and under nails; in the folds of the wrist, elbow and knee; on the buttocks; around the belt line and nipples; and on the penis

When children get scabies, the lesions tend to appear bodywide, including the scalp, palms and soles. A particularly severe, highly contagious form called crusted, or Norwegian, scabies can affect the elderly, AIDS patients and people on immunosuppressants. While people with ordinary scabies usually have no more than 5 to 15 live female mites on their bodies, those with crusted scabies can harbor hundreds, even millions, of adult mites.

The usual treatment is to apply a 5 percent permethrin cream to cool, dry skin from the neck to the bottom of the feet. The cream must be applied everywhere, including the groin, palms and soles and between fingers and toes. The medication, an insecticide, should be left on for 8 to 14 hours, with a possible second application a week or two later in case some eggs survived and had hatched.

Permethrin, a synthetic form of pyrethrin, a natural insect-killing plant chemical, is considered safe for infants and pregnant women, though a 10 percent sulfur ointment and crotamiton cream may be used for infants. To treat the crusted form, an oral medication, ivermectin, is usually prescribed, with a second dose given two weeks later.

In addition to mite-killing medicine, antihistamines and calamine lotion are commonly used to relieve the itching.

To ensure successful eradication of the mites, all members of the household, close friends and sexual contacts must be treated simultaneously. In institutional settings like nursing homes or day care centers, all residents and workers must be treated at the same time. All bedding, towels and clothing used by those infested or potentially infested within three days before treatment must be washed in hot water and dried on high heat or dry-cleaned.

source: herald tribune