CDC — Scabies

Biology

Causal Agent:

Sarcoptes scabiei var. hominis, the human itch mite, is in the arthropod class Arachnida, subclass Acari, family Sarcoptidae. The mites burrow into the upper layer of the skin but never below the stratum corneum. The burrows appear as tiny raised serpentine lines that are grayish or skin-colored and can be a centimeter or more in length. Other races of scabies mites may cause infestations in other mammals, such as domestic cats, dogs, pigs, and horses. It should be noted that races of mites found on other animals may cause a self-limited infestation in humans with temporary itching due to dermatitis; however they do not multiply on the human host.

Life Cycle:

Sarcoptes scabiei undergoes four stages in its life cycle: egg, larva, nymph and adult. Females deposit 2-3 eggs per day as they burrow under the skin . Eggs are oval and 0.10 to 0.15 mm in length and hatch in 3 to 4 days. After the eggs hatch, the larvae migrate to the skin surface and burrow into the intact stratum corneum to construct almost invisible, short burrows called molting pouches. The larval stage, which emerges from the eggs, has only 3 pairs of legs and lasts about 3 to 4 days. After the larvae molt, the resulting nymphs have 4 pairs of legs . This form molts into slightly larger nymphs before molting into adults. Larvae and nymphs may often be found in molting pouches or in hair follicles and look similar to adults, only smaller. Adults are round, sac-like eyeless mites. Females are 0.30 to 0.45 mm long and 0.25 to 0.35 mm wide, and males are slightly more than half that size. Mating occurs after the active male penetrates the molting pouch of the adult female . Mating takes place only once and leaves the female fertile for the rest of her life. Impregnated females leave their molting pouches and wander on the surface of the skin until they find a suitable site for a permanent burrow. While on the skin’s surface, mites hold onto the skin using sucker-like pulvilli attached to the two most anterior pairs of legs. When the impregnated female mite finds a suitable location, it begins to make its characteristic serpentine burrow, laying eggs in the process. After the impregnated female burrows into the skin, she remains there and continues to lengthen her burrow and lay eggs for the rest of her life (1-2 months). Under the most favorable of conditions, about 10% of her eggs eventually give rise to adult mites. Males are rarely seen; they make temporary shallow pits in the skin to feed until they locate a female’s burrow and mate.

Transmission occurs primarily by the transfer of the impregnated females during person-to-person, skin-to-skin contact. Occasionally transmission may occur via fomites (e.g., bedding or clothing). Human scabies mites often are found between the fingers and on the wrists.

Life cycle image and information courtesy of DPDx.

www.cdc.gov

Scabies: Diagnosis and treatment

How do dermatologists diagnose scabies?

A dermatologist can often diagnose scabies by visually examining a patient’s skin from head to toe.

To make sure that a patient has scabies, a dermatologist may remove some skin. This is painless. Your dermatologist will put the skin on a glass slide and look at the slide under a microscope. If your dermatologist sees scabies mites or their eggs, it is certain that you have scabies.

How do dermatologists treat scabies?

To get rid of scabies, treatment is essential. Medicine that treats scabies is only available with a doctor’s prescription.

Who needs treatment?

The person diagnosed with scabies and everyone who has had close contact with that person need treatment. Even people who do not have any signs or symptoms must be treated. This is the only way to prevent new outbreaks of scabies weeks later. People who should be treated include:

Everyone who lives with the person

Recent sexual partners

Most people can be cured with a medicine that they apply to their skin. These medicines are often applied to all skin from the neck down. Infants and young children often need treatment for their scalp and face, too. A dermatologist will provide specific instructions to follow.

Most medicine is applied at bedtime. The medicine is then washed off when the patient wakes up. You may need to repeat this process one week later.

It is important to follow your dermatologist’s instructions. Treating the skin more often than instructed can worsen the rash and itching.

Medicines that may be prescribed include:

5% permethrin cream: This is the most common treatment for scabies. It is used to treat patients 2 months of age and older and women who are pregnant.

10% crotamiton cream

25% benzyl benzoate lotion

Sulfur (5%-10%) ointment

1% lindane lotion

Treatment for widespread scabies

Scabies that covers much of the body and crusted scabies often require stronger medicine. A patient with this type of scabies may receive a prescription for ivermectin. This medicine can be prescribed to children and patients who are HIV-positive. Some patients need only to take one dose, but many need to take two or three doses to cure scabies. The pills are usually taken once every two weeks.

When scabies infects many people at a nursing home, extended-care facility, and other institution, ivermectin may be prescribed to everyone who has a risk of catching scabies.

Other signs and symptoms

Some patients need other treatment, too. Your dermatologist may prescribe:

Antihistamine: To control the itch and help you sleep.

Pramoxine lotion: To control the itch.

Antibiotic: To wipe out an infection.

Steroid cream: To ease the redness, swelling, and itch.

Outcome

Treatment can get rid of the mites, eliminate symptoms such as itch, and treat an infection that has developed. For the first few days to a week, the rash and itch can worsen during treatment. Within four weeks, your skin should heal.

If your skin has not healed within 4 weeks, you may still have mites. Some people need to treat two or three times to get rid of the mites. Be sure to see your dermatologist for treatment. You should never use a scabicide used to treat crops or livestock.

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People who develop crusted scabies, also known as Norwegian scabies, often need repeat treatments to get rid of the mites.

To get rid of the mites and prevent getting scabies again, you have to do more than treat the skin or take a pill. You will need to wash clothes, bedding, and towels to get rid of mites that may have fallen off your skin. You also should vacuum your entire home.

Related AAD resources

References
Centers for Disease Control. «Scabies: Medications.» Last accessed August 2, 2017.

Chosidow O. Clinical practices. «Scabies.» N Engl J Med 2006; 354: 1718-27.

Czelusta A, Yen-Moore A, Van der Straten M et al. «An overview of sexually transmitted diseases. Part III. Sexually transmitted diseases in HIV-infected patients.» J Am Acad Dermatol 2000; 43: 409-32; quiz 33-6.

Elston DM. «Controversies concerning the treatment of lice and scabies.» J Am Acad Dermatol 2002; 46: 794-6.

Habif, Campbell, Chapman, et al. In: Dermatology DDxDeck. 2006. China. Mosby Elsevier. Card #92: «Scabies.»

Jacobson CC, Abel EA. «Parasitic infestations.» J Am Acad Dermatol 2007; 56: 1026-43.

Steen CJ, Carbonaro PA, Schwartz RA. «Arthropods in dermatology.» J Am Acad Dermatol 2004; 50: 819-42, quiz 42-4.

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Scabies Frequently Asked Questions (FAQs)

Scabies is an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The microscopic scabies mite burrows into the upper layer of the skin where it lives and lays its eggs. The most common symptoms of scabies are intense itching and a pimple-like skin rash. The scabies mite usually is spread by direct, prolonged, skin-to-skin contact with a person who has scabies.

Scabies is found worldwide and affects people of all races and social classes. Scabies can spread rapidly under crowded conditions where close body and skin contact is frequent. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks. Child-care facilities also are a common site of scabies infestations.

Crusted scabies is a severe form of scabies that can occur in some persons who are immunocompromised (have a weak immune system), elderly, disabled, or debilitated. It is also called Norwegian scabies. Persons with crusted scabies have thick crusts of skin that contain large numbers of scabies mites and eggs. Persons with crusted scabies are very contagious to other persons and can spread the infestation easily both by direct skin-to-skin contact and by contamination of items such as their clothing, bedding, and furniture. Persons with crusted scabies may not show the usual signs and symptoms of scabies such as the characteristic rash or itching (pruritus). Persons with crusted scabies should receive quick and aggressive medical treatment for their infestation to prevent outbreaks of scabies.

If a person has never had scabies before, symptoms may take 4-8 weeks to develop. It is important to remember that an infested person can spread scabies during this time, even if he/she does not have symptoms yet.

In a person who has had scabies before, symptoms usually appear much sooner (1-4 days) after exposure.

The most common signs and symptoms of scabies are intense itching (pruritus), especially at night, and a pimple-like (papular) itchy rash. The itching and rash each may affect much of the body or be limited to common sites such as the wrist, elbow, armpit, webbing between the fingers, nipple, penis, waist, belt-line, and buttocks. The rash also can include tiny blisters (vesicles) and scales. Scratching the rash can cause skin sores; sometimes these sores become infected by bacteria.

Tiny burrows sometimes are seen on the skin; these are caused by the female scabies mite tunneling just beneath the surface of the skin. These burrows appear as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the skin surface. Because mites are often few in number (only 10-15 mites per person), these burrows may be difficult to find. They are found most often in the webbing between the fingers, in the skin folds on the wrist, elbow, or knee, and on the penis, breast, or shoulder blades.

The head, face, neck, palms, and soles often are involved in infants and very young children, but usually not adults and older children.

Persons with crusted scabies may not show the usual signs and symptoms of scabies such as the characteristic rash or itching (pruritus).

Scabies usually is spread by direct, prolonged, skin-to-skin contact with a person who has scabies. Contact generally must be prolonged; a quick handshake or hug usually will not spread scabies. Scabies is spread easily to sexual partners and household members. Scabies in adults frequently is sexually acquired. Scabies sometimes is spread indirectly by sharing articles such as clothing, towels, or bedding used by an infested person; however, such indirect spread can occur much more easily when the infested person has crusted scabies.

Diagnosis of a scabies infestation usually is made based on the customary appearance and distribution of the rash and the presence of burrows. Whenever possible, the diagnosis of scabies should be confirmed by identifying the mite, mite eggs, or mite fecal matter (scybala). This can be done by carefully removing a mite from the end of its burrow using the tip of a needle or by obtaining skin scraping to examine under a microscope for mites, eggs, or mite fecal matter. It is important to remember that a person can still be infested even if mites, eggs, or fecal matter cannot be found; typically fewer than 10-15 mites can be present on the entire body of an infested person who is otherwise healthy. However, persons with crusted scabies can be infested with thousands of mites and should be considered highly contagious.

On a person, scabies mites can live for as long as 1-2 months. Off a person, scabies mites usually do not survive more than 48-72 hours. Scabies mites will die if exposed to a temperature of 50°C (122°F) for 10 minutes.

Yes. Products used to treat scabies are called scabicides because they kill scabies mites; some also kill eggs. Scabicides to treat human scabies are available only with a doctor’s prescription; no “over-the-counter” (non-prescription) products have been tested and approved for humans.

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Always follow carefully the instructions provided by the doctor and pharmacist, as well as those contained in the box or printed on the label. When treating adults and older children, scabicide cream or lotion is applied to all areas of the body from the neck down to the feet and toes; when treating infants and young children, the cream or lotion also is applied to the head and neck. The medication should be left on the body for the recommended time before it is washed off. Clean clothes should be worn after treatment.

In addition to the infested person, treatment also is recommended for household members and sexual contacts, particularly those who have had prolonged skin-to-skin contact with the infested person. All persons should be treated at the same time in order to prevent reinfestation. Retreatment may be necessary if itching continues more than 2-4 weeks after treatment or if new burrows or rash continue to appear.

Never use a scabicide intended for veterinary or agricultural use to treat humans!

Anyone who is diagnosed with scabies, as well as his or her sexual partners and other contacts who have had prolonged skin-to-skin contact with the infested person, should be treated. Treatment is recommended for members of the same household as the person with scabies, particularly those persons who have had prolonged skin-to-skin contact with the infested person. All persons should be treated at the same time to prevent reinfestation.

Retreatment may be necessary if itching continues more than 2-4 weeks after treatment or if new burrows or rash continue to appear.

If itching continues more than 2-4 weeks after initial treatment or if new burrows or rash continue to appear (if initial treatment includes more than one application or dose, then the 2-4 time period begins after the last application or dose), retreatment with scabicide may be necessary; seek the advice of a physician.

No. Animals do not spread human scabies. Pets can become infested with a different kind of scabies mite that does not survive or reproduce on humans but causes “mange” in animals. If an animal with “mange” has close contact with a person, the animal mite can get under the person’s skin and cause temporary itching and skin irritation. However, the animal mite cannot reproduce on a person and will die on its own in a couple of days. Although the person does not need to be treated, the animal should be treated because its mites can continue to burrow into the person’s skin and cause symptoms until the animal has been treated successfully.

Scabies is spread by prolonged skin-to-skin contact with a person who has scabies. Scabies sometimes also can be spread by contact with items such as clothing, bedding, or towels that have been used by a person with scabies, but such spread is very uncommon unless the infested person has crusted scabies.

Scabies is very unlikely to be spread by water in a swimming pool. Except for a person with crusted scabies, only about 10-15 scabies mites are present on an infested person; it is extremely unlikely that any would emerge from under wet skin.

Although uncommon, scabies can be spread by sharing a towel or item of clothing that has been used by a person with scabies.

Scabies mites do not survive more than 2-3 days away from human skin. Items such as bedding, clothing, and towels used by a person with scabies can be decontaminated by machine-washing in hot water and drying using the hot cycle or by dry-cleaning. Items that cannot be washed or dry-cleaned can be decontaminated by removing from any body contact for at least 72 hours.

Because persons with crusted scabies are considered very infectious, careful vacuuming of furniture and carpets in rooms used by these persons is recommended.

Fumigation of living areas is unnecessary.

Scabies mites do not survive more than 2-3 days away from human skin. Items such as bedding, clothing, and towels used by a person with scabies can be decontaminated by machine-washing in hot water and drying using the hot cycle or by dry-cleaning. Items that cannot be washed or dry-cleaned can be decontaminated by removing from any body contact for at least 72 hours.

The rash and itching of scabies can persist for several weeks to a month after treatment, even if the treatment was successful and all the mites and eggs have been killed. Your health care provider may prescribe additional medication to relieve itching if it is severe. Symptoms that persist for longer than 2 weeks after treatment can be due to a number of reasons, including:

  • Incorrect diagnosis of scabies. Many drug reactions can mimic the symptoms of scabies and cause a skin rash and itching; the diagnosis of scabies should be confirmed by a skin scraping that includes observing the mite, eggs, or mite feces (scybala) under a microscope. If you are sleeping in the same bed with your spouse and have not become reinfested, and you have not retreated yourself for at least 30 days, then it is unlikely that your spouse has scabies.
  • Reinfestation with scabies from a family member or other infested person if all patients and their contacts are not treated at the same time; infested persons and their contacts must be treated at the same time to prevent reinfestation.
  • Treatment failure caused by resistance to medication, by faulty application of topical scabicides, or by failure to do a second application when necessary; no new burrows should appear 24-48 hours after effective treatment.
  • Treatment failure of crusted scabies because of poor penetration of scabicide into thick scaly skin containing large numbers of scabies mites; repeated treatment with a combination of both topical and oral medication may be necessary to treat crusted scabies successfully.
  • Reinfestation from items (fomites) such as clothing, bedding, or towels that were not appropriately washed or dry-cleaned (this is mainly of concern for items used by persons with crusted scabies); potentially contaminated items (fomites) should be machine washed in hot water and dried using the hot temperature cycle, dry-cleaned, or removed from skin contact for at least 72 hours.
  • An allergic skin rash (dermatitis); or
  • Exposure to household mites that cause symptoms to persist because of cross-reactivity between mite antigens.

If itching continues more than 2-4 weeks or if new burrows or rash continue to appear, seek the advice of a physician; retreatment with the same or a different scabicide may be necessary.

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No. If a person thinks he or she might have scabies, he/she should contact a doctor. The doctor can examine the person, confirm the diagnosis of scabies, and prescribe an appropriate treatment. Products used to treat scabies in humans are available only with a doctor’s prescription.

Sleeping with or having sex with any scabies infested person presents a high risk for transmission. The longer a person has skin-to-skin exposure, the greater is the likelihood for transmission to occur. Although briefly shaking hands with a person who has non-crusted scabies could be considered as presenting a relatively low risk, holding the hand of a person with scabies for 5-10 minutes could be considered to present a relatively high risk of transmission. However, transmission can occur even after brief skin-to-skin contact, such as a handshake, with a person who has crusted scabies. In general, a person who has skin-to-skin contact with a person who has crusted scabies would be considered a good candidate for treatment.

To determine when prophylactic treatment should be given to reduce the risk of transmission, early consultation should be sought with a health care provider who understands:

www.cdc.gov

How to Know if That Rash Is Scabies

Good hygiene alone won’t stop the mites that cause the itching of scabies, but it’s a treatable condition.

Sometimes an itch is just a temporary annoyance, but if that itch persists, begins to show as a rash, or gets worse at night, you may have scabies.

This skin condition that causes itching and, typically, raised red spots starts when human itch mites (called Sarcoptes scabiei) burrow under your skin and lay eggs there. In most healthy adults, just 10 to 15 mites can cause scabies.

According to the American Academy of Dermatology, immunocompromised or elderly patients are at greater risk for contracting crusted, or Norwegian, scabies — a form of scabies involving an extreme infestation of thousands of mites — and as a result can become highly contagious.

Scabies can spread quickly in nursing homes, dormitories, camps, and other places where people are crowded together and come in contact with each other. Of course, it can also spread among families and cohabitants once one person brings it into the house. Scabies spreads from person to person, but you don’t get it from pets. Your doctor can help you distinguish scabies from other causes of a rash.

Scabies spreads through contact, not because of a lack of personal hygiene. But doctors say it can be difficult to inform people they have mites because of the stigma associated with them.

“I think a common misconception is that only people who are filthy or dirty get scabies,” says Robin P. Gehris, MD, the chief of pediatric dermatology at the Children’s Hospital of Pittsburgh, part of the University of Pittsburgh Medical Center. “Even royalty, with the right exposure, can get scabies.”

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“It doesn’t present [show up] with symptoms immediately,” says Dr. Gehris. “Unless you’ve had it before, it takes about a month between when the mites set up shop and when it shows up in your skin.”

What It Feels Like to Have Scabies: Signs and Symptoms

Scabies typically starts with itching and a pimple-like rash, often in areas around your wrists, finger webs, elbows, armpits, waist, knees, ankles, or groin. Sex is a common route of infection.

One of scabies’ more distinctive effects happens when it worsens.

“It keeps people up at night — they don’t sleep well, and mentally they get very anxious,” says Adam Goldstein, MD, MPH, a professor of family medicine at the University of North Carolina (UNC) School of Medicine in Chapel Hill.

If you think you may have scabies, a trip to your primary care doctor or dermatologist will often resolve the mystery. Under a microscope, a slide with a sample from the irritated area will typically show the mites.

Solve the Problem: Scabies Treatment That Works

“Primary care doctors can absolutely treat it, but sometimes it doesn’t present as straightforward, so you might end up seeing a specialist,” says Beth Goldstein, MD, a dermatologist in private practice in Chapel Hill and an adjunct at UNC. Dr. Beth Goldstein and Adam Goldstein, MD, MPH, have coauthored guides for physicians on recognizing and treating scabies.

“I have had people with absolutely no rash who are just itchy,” says Amy Kassouf, MD, a dermatologist at the Cleveland Clinic in Ohio. “It’s really an allergic reaction to the mite that makes you so itchy. Not everyone shows that as a rash.”

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While the itching may be unpleasant, treating it is usually fairly straightforward, as long as you follow the recommended steps. When you go to your doctor for treatment, they may recommend an antihistamine and permethrin, which is applied to the skin to kill the mites. Usually, you apply it at bedtime.

“People can itch even if treated, but they will feel progressively better,” says Beth Goldstein.

Two applications of permethrin are recommended. Five to seven days after the first treatment, you’ll need a second treatment with permethrin to kill off mites that have hatched in the interim. This second step is important to prevent having to start the treatment cycle again.

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Getting the Entire Household Scabies Free

In families or households where one person has scabies, you’ll need to be proactive about treating everyone for scabies — even if they don’t have symptoms. That goes for babysitters or frequent visitors like grandparents, too.

“When one family member in a household gets diagnosed, in order to effectively treat that household, you have to treat everyone who lives there — not just the people who have rashes or are itchy,” says Gehris.

“If you don’t successfully treat it, it’s going to continue,” says Dr. Adam Goldstein.

That’s especially important for families to keep in mind. In addition to treating the person with scabies, the bedding, clothes, and towels need to be washed in hot water and dried on a hot setting, or dry-cleaned to rid them of the parasites.

Items that cannot be washed should be sealed in a plastic bag for 72 hours or more to kill the mites. This effectively decontaminates things like toys and other objects handled by the infected person or household members, in order to keep the mites from continuing to spread, notes the Centers for Disease Control and Prevention.

Additional reporting by Deborah Shapiro.

www.everydayhealth.com

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