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Definition

Scabies is an itchy skin condition caused by a tiny burrowing mite called Sarcoptes scabiei. The presence of the mite leads to intense itching in the area of its burrows. The urge to scratch may be especially strong at night.

Scabies is contagious and can spread quickly through close physical contact in a family, child care group, school class, nursing home or prison. Because of the contagious nature of scabies, doctors often recommend treatment for entire families or contact groups.

Scabies is readily treated. Medications applied to your skin kill the mites that cause scabies and their eggs, although you may still experience some itching for several weeks.

Scabies

History

Scabies has been observed in humans since ancient times. Archeological evidence from Egypt and the Middle East suggests scabies was present as early as 494 BC. The first recorded reference to scabies is believed to be from the Bible – it may be a type of “leprosy” mentioned in Leviticus c. 1200 BC or be mentioned among the curses of Deuteronomy 28. In the fourth century BC, Aristotle reported on “lice” that “escape from little pimples if they are pricked” – a description consistent with scabies.

The Roman encyclopedist and medical writer Aulus Cornelius Celsus (25 BC – 50 AD) is credited with naming the disease “scabies” and describing its characteristic features. The parasitic etiology of scabies was documented by the Italian physician Giovanni Cosimo Bonomo (1663–1696) in his 1687 letter, “Observations concerning the fleshworms of the human body”. Bonomo’s description established scabies as one of the first human diseases with a well-understood cause.

In Europe in the late 19th through mid-20th centuries, a sulfur-bearing ointment called by the medical eponym of Wilkinson’s ointment was widely used for topical treatment of scabies. The contents and origins of several versions of the ointment were detailed in correspondence published in the British Medical Journal in 1945.

Epidemiology

Approximately 300 million cases of scabies are reported worldwide each year. Natural disasters, war, and poverty lead to overcrowding and increased rates of transmission.

In industrialized countries, scabies epidemics occur primarily in institutional settings, such as prisons, and in long-term care facilities, including hospitals and nursing homes. Scabies occurs more commonly in fall and winter months in these countries. Prevalence rates for scabies in developing nations are higher than those in industrialized countries.

A survey of children in a welfare home in Pulau Pinang, Malaysia found that the infestation rate for scabies was highest among children aged 10-12 years. The disease was more commonly evident in boys (50%) than in girls (16%). The overall prevalence rate for scabies was 31%.

Of 200 dermatology outpatients in Sirte, Libya, with scabies, the following distribution was found:

• Females – 59%
• Children – 37.5%
• Military personnel – 18%

While many accounts of the epidemiology of scabies suggest that epidemics or pandemics occur in 30-year cycles, this may be an oversimplification of its incidence, since these accounts have coincided with the major wars of the 20th century. Because it is not a reportable disease and data are based on variable notification, the incidence of scabies is difficult to ascertain.

Scabies is clearly an endemic disease in many tropical and subtropical regions, being 1 of the 6 major epidermal parasitic skin diseases (EPSD) that are prevalent in resource-poor populations, as reported in the Bulletin of the World Health Organization in February 2009. Prevalence rates are extremely high in aboriginal tribes in Australia, Africa, South America, and other developing regions of the world. Incidence in parts of Central and South America approach 100%. One report suggests the highest reported rates of the crusted scabies in the world is in remote Aboriginal communities of northern Australia.

Types of Scabies

Many people think that there are different kinds of scabies, but the truth is there is only one type of mite that causes the condition, which is the Sarcoptes scabiei mite. When talking about the classification or types of scabies, what they usually refer is the different ways that the rash can appear. These include:

Typical scabies: These are itchy rashes that appear on the hands, wrists and elsewhere; however, the scalp and face are spared.

Nodular scabies: This type appears as itchy bumps in the groin, armpits and genital areas.

Infantile scabies: A scabies infestation that appears on a child or infant, and are most often characterized by rashes on the hands and feet, as well as the face and scalp.

Another type is complicated scabies, and unlike the others, it does not specify where the rash occurs – rather, this is when scabies occurs with another skin-related condition, such as dermatitis, urticaria, or impetigo (infection).

Scabies may also be classified according to where the infestation breaks out. For example, scabies that affects occupants of a residential facility, such as boarding schools, rest homes, hospitals, prisons and camps is called institutional scabies.

The most severe type of scabies is crusted scabies. Also known as Norwegian scabies, as it was first identified in Norway during the mid-19th century, this severe condition usually occurs in people who are immunocompromised, particularly the elderly, disabled or debilitated.

Risks factors

Scabies can infest any human who comes in contact with the mites, including people in good health. The only known risk factor is direct skin contact with someone who is infested. Good hygiene and health practices cannot prevent transmission if there is close contact with an infected person. The contact one experiences in social or school settings is not likely to be sufficient to transmit the mites. Sexual or other close contact (such as hugging) is required to spread the condition. The condition does appear in clusters, so outbreaks may occur within a given community.

Life cycle

Life cycle of scabies

Causes of Scabies

Scabies is an infestation of the Sarcoptes scabiei mite, also known as the human itch mite.

After burrowing under the skin, the female mite lays its eggs in the tunnel it has created. Once hatched, the larvae move to the surface of the skin and spread across the body or to another host through close physical contact.

Humans are not the only species affected by mites; dogs and cats can also be infected. However, each species hosts a different species of mite, and while humans may experience a mild, transient skin reaction to contact with non-human animal mites, a full-blown human infection with animal mites is rare.

Scabies is highly contagious and spread via direct skin-to-skin contact or by using a towel, bedding, or furniture infested with the mites. As such, some of the most likely people to become infested with mites include:

• Children attending day care or school
• Parents of young children
• Sexually active young adults (and people with multiple sexual partners)
• Residents of extended care facilities
• Older adults

People who are immunocompromised (including those with HIV/AIDS, transplant recipients, and others on immunosuppressant medications)

Symptoms

Itching: This is the main symptom of scabies. This is often severe and tends to be in one place at first (often the hands), and then spreads to other areas. The itch is generally worse at night and after a hot bath. You can itch all over, even with only a few mites, and even in the areas where the mites are not present.

Mite tunnels (burrows): These may be seen on the skin as fine, dark, or silvery lines about 2-10 mm long. They most commonly occur in the loose skin between the fingers (the web spaces), the inner surface of the wrists, and the hands. However, they can occur on any part of the skin. You may not notice the burrows until a rash or itch develops.

Rash: The rash usually appears soon after the itch starts. It is typically a blotchy, lumpy red rash that can appear anywhere on the body. The rash is often most obvious on the inside of the thighs, parts of the tummy (abdomen) and buttocks, armpits, and around the nipples in women. The appearance of the rash is often typical. However, some people develop unusual rashes which may be confused with other skin conditions.

Scratching: Scratching due to intense itching can cause minor skin damage. In some cases the damaged skin becomes infected by other germs (bacteria). This is a secondary skin infection. If skin becomes infected with bacteria it becomes red, inflamed, hot, and tender.

Aggravation of pre-existing skin conditions: Scabies can worsen the symptoms of other skin conditions, particularly itchy skin problems such as eczema, or problems such as psoriasis. Scabies can be more difficult to diagnose in these situations too.

Scabies in hand

Complications of Scabies

Vigorous scratching can break your skin and allow a secondary bacterial infection, such as impetigo, to occur. Impetigo is a superficial infection of the skin that’s caused most often by staph (staphylococci) bacteria or occasionally by strep (streptococci) bacteria.

A more severe form of scabies, called crusted scabies, may affect certain high-risk groups, including:

People with chronic health conditions that weaken the immune system, such as HIV or chronic leukemia

• People who are very ill, such as people in hospitals or nursing facilities
• Older people in nursing homes
• Crusted scabies, also called Norwegian scabies, tends to be crusty and scaly, and to cover large areas of the body. It’s very contagious and can be hard to treat.

Diagnosis and test

Most diagnoses of scabies infestation are made based upon the appearance and distribution of the rash and the presence of burrows. Some common testing methods are:

Microscopic exam of scrapings from suspicious lesions – Scrapings are placed on a slide and examined under a microscope for S. scabiei mites

Burrow Ink Test (BIT) – The suspicious area is rubbed with ink, which is then wiped off. If infestation has occurred, the characteristic zigzag or S pattern of the burrow across the skin will appear.

Topical tetracycline solution – A topical tetracycline solution may be applied to the suspicious area as an alternative to the BIT. The excess solution is wiped off the area with alcohol and examined under a special light to identify the characteristic zigzag or S pattern of the burrow.

Shave biopsy – A fine layer of skin is shaved off at the possible site of infestation and examined under a microscope for evidence of mite infestation.

Needle extraction of mites – A needle is inserted into the length of the burrow and the mite is extracted with the needle and placed on a slide to be examined under a microscope.

The diagnosis of scabies can be especially difficult in elderly persons living in long term care facilities. Their skin is generally dry and scaly and there may be preexisting, chronic dermatological conditions for which oral or topical steroids have been prescribed. Usually, the first indication that a scabies infestation is evolving is complaints of itching and new onset of a rash by one or more residents within a period of 5-12 days.

Exposed health care workers, volunteers and frequent visitors may also complain of itching and rash at about the same time. Skin scrapings, when Georgia Scabies Manual 10 revised: 6/21/12 performed properly, will almost always be positive in persons suspected of having atypical or crusted scabies. However, newly infected persons are more likely to have typical scabies and skin scrapings, even when repeated several time at different sites, may be negative. However, even if a skin scraping or biopsy is negative, it is possible that a person is still infested. Typically, there are fewer than 10-15 mites on the entire body of the infested person, which makes it easy for an infestation to be missed.

Common sites for scabies rash

Scabies can develop anywhere on the skin. The mites, however, prefer to burrow in certain parts of the body. The most common places to have itching and a rash are:

Itching and rash may affect much of the body or be limited to common sites such as:

• Between the fingers
• Wrist
• Elbow
• Armpit
• Penis
• Nipple
• Waist
• Buttocks
• 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.

Common sites for scabies

Treatment and medications

Scabies treatment involves eliminating the infestation with medications. Several creams and lotions are available with a doctor’s prescription. You usually apply the medication over all your body, from your neck down, and leave the medication on for at least eight hours. A second treatment is needed if new burrows and rash appear.

Because scabies spreads so easily, your doctor will likely recommend treatment for all household members and other close contacts, even if they show no signs of scabies infestation.

Medications commonly prescribed for scabies include:

Permethrin cream, 5 percent (Elimite): Permethrin is a topical cream that contains chemicals that kill scabies mites and their eggs. It is generally considered safe for adults, pregnant women, and children ages 2 months and older. This medicine is not recommended for nursing mothers.

Lindane lotion: This medication also a chemical treatment is recommended only for people who can’t tolerate other approved treatments, or for whom other treatments didn’t work. This medication isn’t safe for children younger than age 2 years, women who are pregnant or nursing, the elderly, or anyone who weighs less than 110 pounds (50 kilograms).

Crotamiton (Eurax): This medication is available as a cream or a lotion. It’s applied once a day for two days. This medication isn’t recommended for children or for women who are pregnant or nursing. Frequent treatment failure has been reported with crotamiton.

Ivermectin (Stromectol): Doctors may prescribe this oral medication for people with altered immune systems, for people who have crusted scabies, or for people who don’t respond to the prescription lotions and creams. Ivermectin isn’t recommended for women who are pregnant or nursing, or for children who weigh less than 33 pounds (15 kg).

Although these medications kill the mites promptly, you may find that the itching doesn’t stop entirely for several weeks.

Doctors may prescribe other topical medications, such as sulfur compounded in petrolatum, for people who don’t respond to or can’t use these medications.

Prevention of Scabies

To prevent re-infestation and to prevent the mites from spreading to other people, take these steps:

Clean all clothes and linen: Use hot, soapy water to wash all clothing, towels and bedding used within three days before beginning treatment. Dry with high heat. Dry-clean items you can’t wash at home.

Starve the mites: Consider placing items you can’t wash in a sealed plastic bag and leaving it in an out-of-the-way place, such as in your garage, for a couple of weeks. Mites die after a few days without food.