Scabies is a contagious, extremely itchy, skin disorder that leads to a rash. It is caused by an infestation with a parasite - the scabies mite. The mite lives on the skin and burrows into it. Scabies is spread to others through close skin-to-skin contact. It is easily treated with an insecticide lotion applied to the skin. Two applications of treatment are needed, one week apart.
What is scabies?
Scabies is caused by a mite (like a tiny insect) called Sarcoptes scabiei. The mite is a parasite, meaning it lives off the host (a human) with no benefit to the host.
Scabies mites are tiny. They have a cream-coloured body, bristles and spines on their back, and four pairs of legs. The female mite is bigger (about 0.4 mm x 0.3 mm) compared with the male (0.2 mm x 0.15 mm). The female mites tunnel into the skin and lay eggs. About 40-50 eggs are laid in the lifetime of a mite. The eggs hatch into larvae after 3-4 days, these then grow into adults within 10-15 days. Less than one in 10 eggs becomes an adult scabies mite.
Most of the symptoms of scabies infestation are due to the immune system response to the mites themselves, their saliva, their eggs or their faeces.
The average number of mites on an infested person is 12. Neglected children with scabies in underprivileged communities may have 100s of mites.
How common is scabies?
Scabies is common. In the UK, about 1 in 1,000 people develops scabies each month. Scabies is more common in urban (town) areas, in women and children (probably due to close contact), in the winter (again when people spend more time closer together), and in the North of the country.
How do you get scabies?
You need close skin-to-skin contact with an infected person to catch scabies. This is because the scabies mite cannot jump or fly.
Most cases of scabies are probably caught from prolonged hand-holding with an infected person. The hand is the most common site to be first affected.
Close skin-to-skin contact when having sex is another common way of catching scabies.
The skin-to-skin contact needs to be for a reasonable time to catch the mite. Therefore, you are unlikely to catch scabies from an infected person by casual short contact such as a handshake or a hug. The rate of transmission (spread) is higher the greater the number of mites.
The mites live in skin and can survive away from the host human for about 24-36 hours. You are unlikely to catch scabies from bedding and towels unless you use them immediately after being used by someone with scabies. However, due to the potential risk, it is best to treat bedding and towels by hot washing (described later).
Sometimes outbreaks of scabies occur in places such as nurseries and residential homes, where people are in regular close contact.
- 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.
- Itching. 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 have widespread itching, even with only a few mites.
- 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 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 bacteria - 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.
Note: the itch and rash of scabies are due to an allergy (reaction) to the mites (or their saliva, faeces or eggs). Scabies symptoms usually take 2-6 weeks to occur after you are first infected. The itch and rash can develop on any part of the skin, away from where the mites are actually burrowing. This means that you are infectious (and can spread scabies) before you even know you have scabies.
The picture above shows some typical mite tunnels (burrows) either side of the wrist skin crease. It does not show the typical rash that occurs as a reaction to the mites. For links to many pictures of scabies and other skin conditions see www.patient.co.uk/showdoc/1097/.
Symptoms with recurring infection
The itch and rash normally take 2-6 weeks to develop when you have a first scabies infection. However, if you have scabies, it is cleared with effective treatment and then you are re-infested, the symptoms may be slightly different. In such instances the rash and itching develop much more quickly - often within a day or two. This is because the first scabies infestation has already sensitised your immune system - which reacts much more quickly with this second bout of scabies.
How is scabies diagnosed?
Scabies tends to be diagnosed clinically. This means on the basis of typical symptoms and the typical appearance of the skin rash.
Often, a doctor will find one or more mite burrows on the skin to confirm the diagnosis.
It is sometimes difficult to tell the difference between the rash caused by scabies and some other skin conditions. Therefore, a scraping from the skin is sometimes sent to the laboratory to look for mites under the microscope if there is doubt about the diagnosis.
If itching and a rash develop in several people who live in the same home at about the same time, then scabies is a likely cause.
Who should be treated?
Scabies will persist indefinitely if not treated. Treatment is needed for:
- Anybody who has scabies AND ...
- All household members, close contacts, and sleeping/sexual partners of the affected person - even if they have no symptoms. This is because it can take up to six weeks to develop symptoms after you become infected. Close contacts may be infected, but have no symptoms, and may pass on the mite.
Note: everyone who is treated should be treated at the same time - that is, on the same day.
Scabies is curable. The usual scabies treatment is with permethrin 5% dermal cream. Permethrin is an insecticide that kills the mites. If permethrin cannot be used, an alternative is to use a lotion called malathion 0.5% aqueous liquid. (For example, some people may be allergic to permethrin.)
You can buy both of these products from pharmacies. You can also get them on prescription. They are easy to apply and normally work well if used properly.
Re-apply the same treatment seven days after the first application. This helps to make sure that all the mites are killed.
Daily hot baths, and scrubbing with soap and water will NOT cure a scabies infestation. Insecticide MUST be used.
The following is a general guide about treatment, which gives tips for success:
- Read the leaflet that comes with the product, for exact instructions as to where to apply. Some products are applied to the whole body including the scalp and face, whilst others are to be applied just from the neck down. Remember to include awkward places such as the back, soles of the feet, between fingers and toes, under fingernails, and the genitals. Pay special attention to the areas where mite burrows most commonly occur. That is, the front of the wrists and elbows, beneath the breasts, the armpits, and around the nipples in women.
- An adult needs at least 30 g of cream or 100 ml of lotion to cover the whole body. So, for two applications you will need at least 60 g of cream or 200 ml of lotion per adult.
- Apply cream or lotion to cool dry skin (not after a hot bath).
- The cream or lotion should be left on for the full recommended time. Permethrin cream should be left on for 8-12 hours. Malathion lotion should be left on for 24 hours.
- Children should stay off school until the first application of treatment has been completed.
- If you wash your hands or any other part of your body during the treatment period, you should re-apply the cream or lotion to the washed areas.
- Breast-feeding mothers should wash off the lotion or cream from the nipples before breast-feeding, and re-apply treatment after the feed.
- Put mittens on babies to stop them licking the cream or lotion off their hands.
- Clothes, towels, and bedlinen should be machine washed at 50°C or above after the first application of treatment. This kills the scabies mites. Keep any items of clothing that cannot be washed, in plastic bags for at least 72 hours to contain the mites until they die. Alternative options to kill any mites on clothes and linen are: ironing the item with a hot iron, dry cleaning, or putting items in a dryer on the hot cycle for 10-30 minutes. It is not necessary to fumigate living areas or furniture, or to treat pets.
- Some people who develop a secondary skin infection may also need antibiotics. If you suspect this is the case, you should consult a doctor.
See a doctor if the itch persists longer than 2-3 weeks after treatment. Sometimes the first treatment does not work, and a different one is then needed. The most common reasons why treatment fails (and scabies recurs) are:
- The cream or lotion is not applied correctly for the recommended time.
- A close contact is not treated at the same time, and the infection is passed back.
Note: you will still be itchy for a while after successful treatment
It is normal to take up to 2-3 weeks (and sometimes up to six weeks) for the itch to go completely after the mites have been killed by treatment.
Also, even after successful treatment, in a small number of cases there remain some itchy brownish-red lumps (nodules) up to 2 cm in diameter. If these remain, they most commonly occur on the genitals and armpits. These lumps are neither infectious, nor mean that the mite is still present. They occur in some cases as a prolonged skin reaction to the scabies mite. If they occur, they usually go within three months, but occasionally last up to one year.
Treatment for itching
Itching can be a distressing symptom. It can be eased either with topical treatments that you apply to the skin (such as creams or lotions), or with medication taken by mouth. Your GP or pharmacist can usually advise regarding suitable products. Even cold moisturisers (emollients), especially if they contain menthol, can provide temporary relief. Avoid applying strong steroid creams, especially if the diagnosis of scabies is uncertain.
- Crotamiton cream or lotion has soothing qualities and may help to relieve itch. Apply crotamiton 2-3 times a day (but only once a day for children under three years old).
- Hydrocortisone cream. This is a mild steroid cream that may ease any inflammation and help to ease itch. It can be applied once or twice per day, for up to a week.
- An antihistamine medicine that makes you drowsy, such as chlorphenamine (brand name Piriton®). This does not ease the itch directly, but can help you to sleep if itching is a problem at night (particularly for children). It is not licensed for this use, but can be safely used under the direction of a doctor.
Crusted scabies (Norwegian scabies)
This type of scabies is unusual, and most people who develop scabies do not get Norwegian scabies.
It is a more severe form of scabies with a hyperinfestation of scabies mites. This means that there are thousands or millions of the mites, causing excessive flaking of the skin. Because there are so many mites, and because the skin is flaking off, it is very highly contagious. The rash is crusting (and looks a bit like psoriasis). It can be very extensive and can, if severe, lead to serious secondary bacterial skin infections.
Crusted scabies mainly occurs in people who are immunocompromised (have a poor immune system). This includes people with HIV/AIDS, people having chemotherapy and frail people who are elderly or ill with other conditions. Other people at risk are those who are malnourished, have learning difficulties (meaning they cannot comprehend or respond to the itch) or nerve-related problems (meaning they cannot feel the itch.
Crusted scabies is more easily transmitted through contact with towels, bedding and upholstery. In crusted scabies, the mites can survive for up to a week. Even minimally exposed people, such as cleaners and laundry personnel, are at risk from crusted scabies and need insecticide treatment if they are working in an institution with an outbreak. An outbreak in a institution with many vulnerable people, such as a nursing home, can be extremely challenging. It is likely that all residents and all staff would require treatment.
A healthy person with a normal immune system would develop 'normal' scabies if infested with the scabies mite following contact with someone who had crusted scabies.Crusted scabies may be impossible to eradicate in people with HIV infection, and recurrences are common.
- Scabies; DermNet NZ
- Scabies, DermIS (Dermatology Information System)
- Scabies, Prodigy (December 2011)
- Page TL, Eiff MP, Judkins DZ, et al; Clinical inquiries. When should you treat scabies empirically? J Fam Pract. 2007 Jul;56(7):570-2.
- Strong M, Johnstone PW; Interventions for treating scabies. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD000320.
|Original Author: Dr Tim Kenny||Current Version: Dr Katrina Ford||Peer Reviewer: Dr Tim Kenny|
|Last Checked: 15/03/2012||Document ID: 4325 Version: 42||© EMIS|
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