Being aware of the clinical features of scabies can help ensure that the affected individual receives a prompt diagnosis and effective treatment. A cycle of infection can be initiated if more than one person has scabies. There is some evidence that scabies is becoming more common and, on occasion, difficult to treat (Sunderkötter et al, 2021). Older adults are more vulnerable to scabies due to age-related changes (Nigam and Knight, 2017). This article will examine the clinical features of scabies, how it is treated and how to manage its complications.
What is scabies?
Scabies is one of the most common dermatological conditions and affects more than 200 million people at any given time. While scabies occurs worldwide, it is most common in hot, tropical countries and in areas of high population density (World Health Organization (WHO), 2020).
Scabies is caused by a small mite called Scaroptes scabei. There are two classes of scabies infection, both of which are caused by the same mite. These are: classical scabies (present in people with normal immune systems) and hyperkeratotic scabies. In classical scabies, there are 12-20 mites in the body in a typical infestation. Hyperkeratotic scabies (also known as atypical scabies, crusted scabies and Norwegian scabies) is a super infestation that occurs in people with immunodeficiencies and in some frail older adults. There can be hundreds, or even thousands, of mites. The skin can become thickened, scaled and crusted. The crusts can break off and mites can live in the crusts for some days, increasing infection risks. Hyperkeratotic scabies is highly infectious (Bernigaud et al, 2020). Figure 1 illustrates the differences between a classical scabies infection and a superinfection.
How is scabies transmitted
Scabies is spread from one person to another during prolonged skin contact. Normally, it takes 5–10 minutes of skin contact to allow the mite enough time to transfer to the other person. When the mite (usually a pregnant female) crawls from one person's skin to another, it burrows into the skin within 30 minutes of contact. The mite lays around three eggs in each burrow. The mite lays two eggs daily for up to 2 months. The eggs hatch in 2–4 days and are mature in 2 weeks, after which, the young mites mate and begin to lay their own eggs (WHO, 2020).
Scabies mites need to live in warm, moist conditions, so they do not move, unless they can transfer from one person to another. This means that scabies mites do not normally transfer from clothes, furnishings and flooring to others. Transmission of mites from the environment to others is possible but unlikely, unless there is a case of Norwegian scabies (NHS Choices, 2020; Centre for Disease Control, 2022).
Scabies normally spreads when people have prolonged skin-to-skin contact. A person who shakes the hand of a someone with scabies is not at risk. However, a person who holds hands with an affected person, or who shares a bed with them, is at risk.
Clinical features
The symptoms of scabies are itch, rash, the presence of tunnels in the skin and sometimes, secondary infection. The itch and rash of scabies are caused by an allergy to the faeces of the mites. It can take 2–6 weeks for the itching to begin. If a person has had scabies in the past, itching occurs sooner as the body has become sensitised to the allergen. The person with scabies can pass it on before he or she has been diagnosed with scabies. When people have a rash all over their body, they often believe that there are lots of mites crawling under their skin. Usually, a person with scabies has around 12–20 mites in the body. The allergy is what causes the person to itch all over and to develop a rash.
The itch is often severe and the person affected may scratch and tear the skin, causing bleeding. Scratching can open the tunnels and kill the mites. Itching tends to start in one area at first (often the hands), and then spreads to other parts of the body. The itch tends to be worse at night and after a hot bath.
A rash usually appears soon after the itch starts. It is usually a blotchy red rash that can appear anywhere on the body. On darkly pigmented skin, the rash can look brown or black. The rash is often most obvious on the inside of the thighs, parts of the abdomen and the ankles.
Mite tunnels (burrows) may be seen on the skin as fine, dark or silvery lines, about 2–10 mm long. These can be seen most easily with a magnifying glass and a torch. The most common areas where they occur are the skin between the fingers, the wrists and elbows, the groin, armpits, breasts, nipples, scrotum and penis.
Scratching usually causes skin damage and can lead to infection. Skin infected with bacteria becomes red, inflamed, hot and tender. The infected skin may make diagnosis difficult because it masks signs of tunnelling. Figure 2 shows an infected scabies rash.
History
A person normally has scabies for 2–6 weeks before itching occurs (WHO, 2020).
It is important to enquire about the onset, what makes the itch worse or provokes itching, and what helps improve or palliates symptoms. The onset of itching is important. If the itching developed suddenly, then it is likely to be caused by infestation (such as scabies), medication or an allergy.
People who have scabies will often report that itching gets worse in the evening and at night. If the patient reports this, you should ask if anyone else that the person has close contact with is showing similar symptoms. If the person is itching especially at night and has friends who are also itching, then the likely diagnosis is scabies (Primary Care Dermatology Society, 2022).
Physical examination
It is important to inspect all of the person's skin. This examination enables the clinician to check if itching and any rashes are widespread or localised.
Localised itching may indicate contact dermatitis. Common allergies include rubber (found in bra straps, and hold up and compression stockings), nickel (present in coins, buckles, belts and bra straps), fragrance (found in perfume, shampoo, soap and cosmetics), and preservatives found in toiletries, cosmetics and moisturisers. Figure 3 illustrates the distribution of the scabies rash.
Diagnosing scabies
Sometimes, older adults do not have all the classical signs and symptoms of scabies, which makes diagnosis difficult (Berger and Steinhoff, 2011). Older adults may not have any signs of finger webbing and can have facial lesions (Raffi et al, 2019). Diagnosing scabies in older people in care homes who are unable to give a clear history due to cognitive impairment can also be difficult (Cassell et al, 2018). An ink test can be used to identify the burrows of scabies mites. Ink is rubbed around an area of itchy skin before being wiped off with an alcohol wipe. If scabies burrows are present, some of the ink will remain and will have tracked into the burrows, showing up as a dark line (NHS Inform, 2022).
Scabies can only be diagnosed with absolute certainty if a scabies mite is obtained from the skin and observed under a microscope. The mite is usually acquired by scraping the skin over a lesion with a blunt scalpel and transferring the skin scraping to a microscope slide (Figure 4).
Some clinicians are not highly experienced in obtaining skin scrapings. In this case, they can identify a skin lesion, press sellotape firmly over the lesion and peel it away. This is then sent to the dermatologist or the laboratory for confirmation of scabies (Katsumata and Katsumata, 2006). Normally, diagnosis is made without microscopic confirmation.
Treatment
Scabies treatment varies according to the type of scabies and whether the person is at home, in a care home or hospital. The way scabies is treated depends on whether there is a single case or an outbreak. If there is a single case of classical scabies, the individual and any close contacts may be treated.
The usual treatment is either a cream containing permethrin 5% or a lotion containing malathion 0.5%. These kill the scabies mite (UK Government, 2022).
Normally, people who have a confirmed case of scabies are treated twice: following the initial treatment, the second treatment is reapplied 7 days later. The reason the treatment is repeated is because scabicides are more effective at killing mites than eggs. The second treatment aims to kill any eggs that survived the first treatment and hatched into mites.
It is not necessary to give someone a hot bath before treating scabies. Scabies treatments are more effective when applied to cool skin. Staff should wear gloves and avoid prolonged skin contact when treating a person with scabies. The cream or lotion should be applied to all parts of the body (and not just the areas with a rash). It is important to ensure that the cream or lotion is applied to areas such as the webs between fingers, under the breasts and in skin folds. An adult will require at least one 30 g tube of cream and larger adults may require two tubes. If a lotion has been prescribed, an adult will require at least 100 ml of lotion. The lotion comes in a 500 ml bottle, so you may find it helpful to measure out 100 ml to ensure that you have used enough.
The cream or lotion should be left on for the recommended time, usually 24 hours, and the person should have a bath or shower after to remove the cream/lotion and prevent skin irritation.
Norwegian scabies is normally treated by specialists. It may be treated with a combination of an oral product such as ivermectin and 2–3 applications of topical treatment on consecutive days (UK Government, 2022).
The usual advice is for the person to launder bedding, clothing that is currently worn and towels that are in use. NHS Choices (2020) and the UK Government (2022) advise people with scabies to wash all bedding and clothing in the house at 50°C or higher on the first day of treatment and put clothing that cannot be washed in a sealed bag for 3 days until the mites die.
Infection control measures
In hospitals and care homes, infection control measures should be used to reduce the risks of infection. Normally, bed linen, towels and clothing are treated as infected and sent to the laundry in a red bag. The person should not have close physical contact with others until treatment is completed. This is especially important when dealing with hyperkeratotic scabies and staff should seek expert advice from infection control and public health staff.
At home, the person should not share a bed or have close physical contact with other people until treatment is completed. The person should not share towels or clothing with others. Figure 5 outlines how scabies can be managed in a care home.
Treating contacts
Usually, anyone living in the same house—partners and others—who have significant contact will require treatment. Contacts can be infected with scabies but remain asymptomatic for several weeks. All contacts need to be treated; people who do not have symptoms will only require one treatment and those who have symptoms will require two (Primary Care Dermatology Society, 2022).
Work and school
Adults and children who have been treated for scabies can return to work and school 24 hours after their first scabies treatment, respectively.
Treating itch
An itch occurs because C fibres in the skin pass signals to the dorsal horn of the spinal cord. These travel to the thalamus, where there are specific itch fibres. The itch signals also stimulate the motor cortex in the brain and produce the urge to scratch (Ward and Bernhard, 2005) (Figure 6). Certain naturally occurring chemicals such as serotonin, histamine and prostaglandins stimulate C fibres and cause itching (Chung et al, 2020).
People who have scabies can continue to itch for 2–3 weeks after successful treatment. If the rash has become infected, then an antibiotic may be required. Itching can be treated with an antihistamine tablet or with a cream containing hydrocortisone 1%. The hydrocortisone treats the allergy that causes the itch. This is only given for a week as it can damage the skin if used long-term. Itching is often worse at night and can disturb sleep. Older antihistamines such as Chlorphenamine, which are given at night, promote drowsiness and can help a person get a good night's sleep.
Conclusion
Scabies may be more common than in the past. It can be difficult to diagnose and treat. Diagnosis and effective treatment is essential to avoid recurrence as this can affect physical and mental health.
Key points
- Scabies is associated with over-crowding and living in institutions such as care homes, prisons and homelessness
- Infection occurs some weeks before people develop symptoms such as an itch
- Topical treatment, washing clothing, towels and bedding normally eliminate scabies
CPD reflective questions
- What symptoms would make you suspect that a person had scabies?
- Will this article affect the way you provide patient care and treatment?
- What would you do to prevent the spread of scabies in a hospital ward?