At a glance
- Scabies is the result of contact with the Sarcoptes scabiei mite. The femal mite burrows into the skin and lays eggs. When the eggs hatch, the cycle repeats itself.
- Scabies is species-specific. While animal mites, such as the ones that cause canine mange, can cause pruritus in humans, the parasites cannot survive or breed.
- A scabies scrape should be performed so that proper diagnosis and treatment can be offered.
- Permethrin (Elimite) is effective when used as directed.
Scabies is an intensely pruritic skin condition caused by infestation with the microscopic mite Sarcoptes scabiei. Millions of people worldwide are affected, and in the United States, the rate of infestation has been increasing for several years. All populations are susceptible, regardless of gender, race, or age, although children younger than 15 years are most frequently afflicted. People with multiple sex partners, those who are immunocompromised, and clinicians in direct patient contact are also at high risk for contracting the disease.
Infestation occurs following contact with the S. scabiei mite. The female insect burrows into the skin, most commonly on the fingers, hands, wrists, heels, elbows, armpits, inner thighs, and waist. She proceeds to lay up to three eggs daily for about five weeks. When the eggs hatch, the new mites repeat the cycle. The intense pruritus that accompanies scabies is an allergic reaction to the mites, their eggs, or their feces.
A diagnosis of scabies can cause apprehension in the patient as well as the clinician. Patients and their families are often disgusted and frightened by the prospect of having “bugs,” and as word spreads among their circle of friends, a ripple effect is felt by the entire local medical community, with phones ringing off the wall. Two related issues stand out with regard to scabies: diagnosis and treatment. Neither is all that simple because scabies is both vastly overdiagnosed and frequently missed. This article examines the 10 most common myths surrounding this frequent condition.
Myth: Scabies is highly contagious.
Reality: Yes, scabies is contagious, but diagnosis of an acquaintance does not automatically mean your patient will contract the disease. Infection requires prolonged skin-to-skin contact, so a person cannot easily acquire the mites by shaking hands or from touching inanimate objects. If this were the case, everyone would have scabies. Scabies is often transmitted sexually but usually only in cases where skin-to-skin contact is lengthy (e.g., sleeping together all night), not from brief encounters.
A detailed history of personal contacts as well as a thorough understanding of the relative difficulty with which scabies is acquired are vital when ruling out or diagnosing scabies.
Myth: Numerous ectoparasites infest Americans.
Reality: In this country, among those who bathe daily, scabies is the only ectoparasite worth mentioning. It is vastly more common than lice infestations. Pubic lice are rare and almost always sexually transmitted. Body lice are mainly relegated to those with extremely poor hygiene and diet. And while head lice are quite common, they do not infest the rest of the body. Additional insects commonly found in the United States include fleas, chiggers, and bedbugs, but they do not reside or multiply on humans. There are a number of human ectoparasites that can be acquired in foreign countries, such as sand fleas and botflies, so it is important to ask patients about recent travel.
Knowing that scabies mites are the only “bugs” that reside and multiply on the human body and cause widespread itching makes it easier to diagnose an infestation. If scabies is ruled out, there are no other “bugs” to worry about. For concerned patients, this is a fact worth repeatedly emphasizing.
Myth: Scabies can be passed between humans and household pets.
Reality: While animal forms do exist, scabies is species-specific. Canine scabies is known as “mange.” These mites can crawl on humans, producing itching, but they will be unable to multiply and will soon die. And while human S. scabiei presumably can infest dogs and other pets, the mites cannot survive for extended periods or carry out their life cycle. So although humans may develop symptoms of an animal scabies infection, they do not have to be treated for the disease. Occasionally in our practice, a clinician will see a patient with pruritus secondary to a pet’s scabies. A recent example was a young girl who developed an itchy rash on her chest and arms after clutching a pet rabbit. In such cases, it is best to get the animal treated and/or put more distance between the person and pet. A topical steroid cream can be applied to the patient’s rash to ease the pruritus.
Myth: Scabies is easy to diagnose.
Reality: Often, patients will present with an extremely pruritic bumpy rash, which increases in intensity at bedtime. Frequently, they are quickly diagnosed with scabies, and treatment is instituted. But many of these patients never actually had scabies. Instead, they may have had one of several conditions in the differential, such as atopic dermatitis, xerosis (especially common in the elderly and during cold weather), contact vs. irritant dermatitis, or a medication reaction. All of these are exacerbated by anti-scabies medications.
The truth is that scabies is often difficult to diagnose. It frequently presents with minimal and/or atypical findings. However, there are certain signs for which clinicians should remain alert: persistent constant itching despite application of numerous medications; suboptimal patient hygiene; patient age and history of sexual activity; vesicular rash on the hands, especially between the fingers or on the volar wrists, thenar/hypothenar skin, and suprapubic skin; edematous red papules on the scrotum and/or penis; and additional family members similarly affected. The presence of burrows (thin, dark, wavy lines created by the female mites as they tunnel under the skin) is extremely helpful when making a diagnosis, but such obvious signs often are not seen.
The trouble with the aforementioned findings is that mites usually aren’t noticed unless one is looking specifically for them, and they usually aren’t looked for unless scabies is considered part of the differential in a not-so-obvious case.
Myth: Bedtime exacerbation of itching is pathognomonic for scabies.
Reality: Virtually all pruritic conditions worsen when the patient lies down to sleep. During the day, patients are distracted from the itching, so it does not become a problem until their only task is getting to sleep.
Myth: Presumptive diagnosis and treatment of scabies is reasonable in primary care.
Reality: In many primary-care settings, scabies is diagnosed and treated presumptively without consideration for other diagnostic possibilities. This can cause problems, not only for the patient but eventually for the patient’s circle of contacts. When treatment for scabies fails in a patient with one of the differential conditions, the person feels compelled to consult another provider who, most likely, will try another empirical treatment. It is best for everyone involved if a specific diagnosis can be obtained, and in the case of scabies, that means performing a scabies scrape.
Myth: Scabies scrapes are difficult and time-consuming to perform.
Reality: This is a common myth in primary care. Often, scabies scrapes aren’t performed because clinicians don’t know how to do them or they don’t see the necessity. In truth, performing and reading scrapes is simple and no less important than obtaining an x-ray to rule out pneumonia or urinalysis to confirm a bladder infection.
This procedure takes a maximum of four to five minutes. When you find what you’re looking for, you can return to the exam room and tell your patient what he or she has with complete confidence.
Myth: Scabies is often resistant to treatment.
Reality: While lindane is no longer uniformly effective for treating scabies, permethrin (Elimite) is effective when used as directed. Treatment failure is usually the result of how the treatment was performed rather than what medication was used. As previously mentioned, the single most common cause of treatment failure is the fact that the patient never had scabies in the first place. When the patient actually is diagnosed with recurrent scabies, attention must be given to the treatment details outlined below.
Myth: Environmental cleanup is a crucial component of treatment.
Reality: When most patients hear the word “scabies,” their only frame of reference is fleas. In contrast to fleas, which can live in or on such inanimate objects as carpets, scabies mites will only survive for a short time off the human body (usually less than two days). They typically do not lay eggs on or reside in inanimate objects, so even though cleaning the surrounding environment makes some sense, it is more important to identify the source of the infestation and thoroughly treat all contacts.
Clinicians should emphasize treatment over environmental cleanup because many patients pay so much attention to steam-cleaning their entire house that they neglect treatment issues. It should be noted that dealing with scabies in an institutional setting (nursing home, mental hospital, etc.) requires increased emphasis on environmental cleanup because the exposure time is greater.
When cleaning the environment, make sure to change the bedding, towels, and sleepwear; vacuum the couch; and place any stuffed toys in the freezer for a week or two.
Myth: Adequate treatment results in the immediate cessation of symptoms.
Reality: Treatment regimens must be followed specifically. All contacts should be treated twice, at the same time, seven days apart (to allow any eggs to hatch). During this period, suspicious contacts should be avoided (especially children and sexual partners). Permethrin should be applied to every skin surface below the neck, including under freshly cleaned fingernails. This site is often overlooked, and scratching can cause the condition to spread. On babies, unlike older children and adults, scabies can infest scalps and soles, so these areas must also be treated.
Unfortunately, the pruritus associated with scabies can and often does persist for weeks following treatment, although the intensity does decrease with time. Patients frequently call back within a week or two to complain about the itching, so it’s important to be completely certain about the diagnosis. Without certainty, treatment is often changed, usually to a steroid, which will make scabies worse, if in fact the patient has it. It is important to educate the patient about the likelihood of continuing symptoms.