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Scabies Causes/Scabies is an intensely itchy dermatosis caused by the mite Sarcoptes scabiei. A patient with ordinary scabies may have an average of 12 mites; however, those with crusted scabies may have thousands of mites. The infestation occurs at all ages, but particularly in children. It is a common public health problem in poor communities and is widespread in many underdeveloped countries. Scabies is highly contagious, and person to person spread occurs via direct contact with the skin. Transfer from clothes and bedding occurs rarely and only if contaminated by infected people immediately beforehand.[rx]
Scabies is an infestation of the skin by the mite Sarcoptes scabiei. Typical sites of infestation are skin folds and flexor surfaces. In adults, the most common sites are between the fingers and on the wrists, although infection may manifest in older people as a diffuse truncal eruption. In infants and children, the face, scalp, palms, and soles are also often affected. Infection with the scabies mite causes discomfort and intense itching, particularly at night, with irritating papular or vesicular eruptions. The discomfort and itching can be especially debilitating in immunocompromised people, such as those with HIV/AIDS.
Types of Scabies
There’s only one type of mite that causes a scabies infestation. This mite is called Sarcoptes scabiei. However, these mites can cause several types of infestations.
- Typical scabies – This infestation is the most common. It causes an itchy rash on the hands, wrists, and other common spots. However, it doesn’t infest the scalp or face.
- Nodular scabies – This type of scabies may develop as itchy, raised bumps or lumps, especially in the genital areas, armpits, or groin.
- Norwegian scabies – Some people with scabies may develop another form of scabies known as Norwegian scabies, or crusted scabies. This is a more severe and extremely contagious type of scabies. People with crusted scabies develop thick crusts of skin that contain thousands of mites and eggs.
Crusted scabies can also appear
- easy to crumble when touched
Crusted scabies usually develops in people with weakened immune systems. This includes people with HIV or AIDS, people who use steroids or certain medications (such as some for rheumatoid arthritis), or people who are undergoing chemotherapy.
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 of Scabies
The onset of symptoms of scabies varies depending on whether or not a person has previously been exposed to mites. The first time a person is exposed to the scabies mite, it can take upwards of 2 to 6 weeks[rx] for symptoms to develop. This time frame is significantly shorter in subsequent infestations as the body’s immune system is quicker to react, typically within 1 to 4 days.
Signs and symptoms of scabies include:
- Itching – This is often worse at night and can be severe and intense. Itching is one of the most common scabies symptoms.
- Rash – When the mite burrows into the skin, it forms burrow tracks, or lines, which are most commonly found in skin folds, and resemble hives, bites, knots, pimples, or patches of scaly skin. Blisters may also be present.
- Sores – These occur in infested areas where a person has scratched at the skin. Open sores can lead to impetigo, commonly caused by secondary infection with Staphylococcus aureus.
- Thick crusts – Crusted scabies, also known as Norwegian scabies, is a form of severe scabies in which hundreds to thousands of mites and mite eggs are harbored within skin crusts, causing severe skin symptoms.
Most often, those affected with crusted scabies exhibit widespread, gray, thick, crumbling crusts.
Mites living in the detached crusts can live for upwards of a week without needing human contact due to the food provided by the crusts themselves.
The most common site of infestation in adults and older children include:
- in between the fingers
- around fingernails
- inner parts of the wrists
- inner elbow
- soles of the feet
- the breasts, particularly the areas around the nipples
- male genitalia
- shoulder blades
Infants and young children experience infestation in other areas of the body, including the:
- palms of the hands
- soles of the feet
Diagnosis of Scabies
Other ways to make a definitive diagnosis for scabies include:
skin scraping (scraping an oil-covered scalpel blade across a burrow and examining the sample microscopically),
a burrow ink test (covering a lesion with ink and removing it with alcohol leaves ink tracking in the burrows),
dermatoscopy (direct visualization of magnified skin). This option is not practical in many locations, especially remote communities.[rx]
Products used to kill scabies mites are called scabicides. No “over-the-counter” (non-prescription) products have been tested and approved to treat human scabies.
The following medications for the treatment of scabies are available only by prescription.
Classic scabies: one or more of the following may be used
- Permethrin cream 5% Brand name product – Elimite Permethrin is approved by the US Food and Drug Administration (FDA) for the treatment of scabies in persons who are at least 2 months of age. Permethrin is a synthetic pyrethroid similar to naturally occurring pyrethrins which are extracts from the chrysanthemum flower. Permethrin is safe and effective when used as directed. Permethrin kills the scabies mite and eggs. Permethrin is the drug of choice for the treatment of scabies. Two (or more) applications, each about a week apart, may be necessary to eliminate all mites. Children aged 2 months or older can be treated with permethrin.
- Crotamiton lotion 10% and Crotamiton cream 10% Brand name products: Eurax ; Crotan Crotamiton is approved by the US Food and Drug Administration (FDA) for the treatment of scabies in adults; it is considered safe when used as directed. Crotamiton is not FDA-approved for use in children. Frequent treatment failure has been reported with crotamiton.
- Sulfur (5%-10%) ointment (multiple brand names) Sulfur in an ointment base (petrolatum) is safe for topical use in children, including infants under 2 months of age. The odor and cosmetic quality may make it unpleasant to use (CITE KARTHIKEYAN 2007).
- Lindane lotion 1% Brand name products: None available insane is an organochloride. Although FDA-approved for the treatment of scabies, lindane is not recommended as first-line therapy. Overuse, misuse, or accidentally swallowing lindane can be toxic to the brain and other parts of the nervous system; its use should be restricted to patients who have failed treatment with or cannot tolerate other medications that pose less risk. Lindane should not be used to treat premature infants, persons with a seizure disorder, women who are pregnant or breast-feeding, persons who have very irritated skin or sores where the lindane will be applied, infants, children, the elderly, and persons who weigh less than 110 pounds.
- Ivermectin Brand name product: Stromectol Ivermectin is an oral antiparasitic agent approved for the treatment of worm infestations. Evidence suggests that oral ivermectin may be a safe and effective treatment for scabies; however, ivermectin is not FDA-approved for this use. Oral ivermectin should be considered for patients who have failed treatment with or who cannot tolerate FDA-approved topical medications for the treatment of scabies. If used for classic scabies, two doses of oral ivermectin (200µg/kg/dose) should be taken with food, each approximately one week apart. The safety of ivermectin in children weighing less than 15 kg and in pregnant women has not been established.
Note that although ivermectin guidelines recommend taking on an empty stomach, scabies experts recommend taking with a meal to increase bioavailability (CITE NEJM Currie article).
Crusted scabies: both oral and topical agents should be used
- Ivermectin – Brand name product: StromectolIvermectin is an oral antiparasitic agent approved for the treatment of worm infestations. Evidence suggests that oral ivermectin may be a safe and effective treatment for scabies; however, ivermectin is not FDA-approved for this use. The safety of ivermectin in children weighing less than 15 kg and in pregnant women has not been established.
For crusted scabies, ivermectin should be administered together with a topical agent. Oral ivermectin (200µg/kg/dose) should be taken with food. Depending on infection severity, ivermectin should be taken in three doses (approximately days 1, 2, and 8), five doses (approximately days 1, 2, 8, 9, and 15), or seven doses (approximately days 1, 2, 8, 9, 15, 22, and 29).
- Permethrin cream 5% – Brand name product: ElimitePermethrin is approved by the US Food and Drug Administration (FDA) for the treatment of scabies in persons who are at least 2 months of age. Permethrin is a synthetic pyrethroid similar to naturally occurring pyrethrins which are extracts from the chrysanthemum flower. Permethrin is safe and effective when used as directed. Permethrin kills the scabies mite and eggs. Permethrin is the drug of choice for the treatment of scabies. Topical permethrin should be administered every 2-3 days for 1-2 weeks to treat crusted scabies.
- Benzyl benzoate 25% (with or without tea tree oil) – Benzyl benzoate may be used as an alternative topical agent to permethrin. However, this agent may cause immediate skin irritation. Lower concentrations may be used in children (10% or 12.5%).
- Keratolytic cream – A topical keratolytic cream may also be used to help reduce the crusting of the skin and aid in the absorption of the topical permethrin or benzyl benzoate.
Topical benzyl benzoate versus topical sulfur ointment:
- We found one systematic review (search date 2010), which identified one RCT (158 adults and children) comparing topical benzyl benzoate with topical sulfur ointment.
- Topical benzyl benzoate compared with topical sulfur ointment We don’t know how topical benzyl benzoate and topical sulfur ointment compare at reducing the proportion of people with treatment failure at 15 days (low-quality evidence[Rx].
|Treatment||Application period||Repeat||Age restrictions||Caution(s)||Other comments|
|5% permethrin cream (Nix Dermal Cream*, Kwellada-P Lotion†)||Leave on for 12–14 h, followed by bathing||7 days||>3 months of age||Consider as first-line treatment|
|10% crotamiton lotion/cream (Eurax Cream)||24 h||May be repeated in 24 h; wash off 48 h after last application||Skin irritation and contact dermatitis||Consider as second-line treatment|
|Sulphur (8%–10%) precipitated in petroleum jelly (compounded)||Daily for 3 consecutive days||No||Safe in pregnancy and for infants||Effective but not commonly used due to messy application and odour|
|Benzyl benzoate 28% in adults, 10%–12.5% in children||24 h||May be repeated 1 day apart||Caution in pregnancy||Not available in North America but widely available elsewhere|
|1% Lindane cream||Apply 8–12 h for adults, 6–8 h for children, followed by bathing||Only if new mites or papules after 7 days of treatment||Use with caution in small children||Associated with neurotoxicity, ataxia, tremors and bone marrow suppression||Consider as second-line treatment only|
|Ivermectin (oral) for outbreak (Stromectol, Mectizan‡)||Single dose oral 200 mcg/kg||May need to be repeated in 2 weeks||Safety not established in infants <15 kg, pregnant or lactating women||Not licensed in Canada§|
|Ivermectin (oral) for crusted scabies (Stromectol, Mectizan‡)||Single dose oral 200 mcg/kg||Multiple repeat doses with keratolytics¶ and consider combination with 5% permethrin||Safety not established in infants <15 kg, pregnant or lactating women||Not licensed in Canada§|
How can I keep from getting scabies
- Abstinence (not having sex) is the best form of prevention.
- Mutual monogamy (having sex with only 1 uninfected partner who only has sex with you) is effective.
- Limit the number of sexual partners to reduce exposure to all STDs.
- Use latex condoms for all types of sexual penetration (oral, vaginal, anal). Note: Latex condoms, when used consistently and correctly, can reduce the risk of transmission of other STDs, but are not considered effective against scabies.
- Know your partner(s). Careful consideration and open communication between partners may protect all partners involved from infection.
- Have regular check-ups if you are sexually active.
- If you have an STD, don’t have sex (oral, vaginal, or anal) until all partners have been treated.
- Prompt, qualified, and appropriate medical intervention and treatment and follow-up are important steps in breaking the disease cycle.