Dr Cathy Stephenson: 'There has recently been a flurry of scabies'
Apologies if you are reading this while you eat your morning cereal... it's probably not ideal breakfast reading!
But I have it on good authority that there has recently been a flurry of scabies cases in my area, hence I thought it timely to give some background information about what scabies is, how to tell when you have it, and what treatments work.
Scabies is thought to be one of the oldest recognised diseases – the parasitic mite that causes it (Sarcoptes scabiei) has been responsible for itchy rashes in humans for more than 2,500 years.
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In fact, the name scabies comes from the Latin word scabere, meaning "to itch". Since those early days, the scabies mite has thrived, and is now the cause of a massive global health problem, leading to significant morbidity and even mortality in developing countries. In more developed parts of the world, we are fortunate: although scabies infests large number of us, it is easily treated and very rarely leads to any severe complications.
Being infected by the scabies mite requires skin-to-skin contact with an infected person, and the contact need only be short-lived – for example holding hands. It can also be transmitted by sexual contact, and occasionally via bedding or furnishings, although this is a rarer mode of transmission than is commonly thought.
Because it requires close contact, scabies does tend to occur in poor or overcrowded living conditions – so outbreaks are common in places such as refugee camps, schools and institutions such as hospitals, prisons and rest homes. You are also more likely to contract scabies if you have a weakened immune system, for example through poor nutrition, long-term steroid use, immunosuppressant treatment or chemotherapy.
The female scabies mite is about 0.4mm in length, double the size of her male counterpart. They meet on the surface of the hosts skin, mate and then he dies, leaving her to burrow into the skin to lay her eggs. The eggs hatch and mature to adult mites, a process which takes 10-15 days – the adults die at around a month old. An "average" person with scabies will have about 12 mites in their skin, but this number can be much greater in immunocompromised people.
The symptoms of scabies take about four weeks to appear after initial infestation, and are not due to the mite itself – they are actually an allergic response to the mites eggs and faeces.
THE NEED TO ITCH
The symptoms can mimic other skin problems, making it difficult to detect. The overwhelming complaint in sufferers seems to be the high degree of itch all over the body – patients often describe this as the itchiest thing they have ever had, and it frequently disrupts sleep due to the incessant need to scratch. The itch seems to be worse when people are warm, so cool showers and reducing the amount of bedding can help alleviate it a little.
There is usually a rash, but this varies in appearance from person to person. It can look like raised, red bumps on the skin, scabby patches or appear more like tiny blisters just under the skin surface. Characteristically, there are lots of visible scratch marks known as excoriations around the affected areas. The scabies rash tends to spare the face and scalp, but all other body parts can be affected, most commonly limbs, trunk, armpits, breasts and groin.
Fit healthy people with scabies don't usually become seriously unwell from an infection, although it is undoubtedly unpleasant and disruptive. But the degree of scratching does pre-dispose to bacterial skin infections, which can be really serious in more vulnerable people, and need to be treated promptly. This can appear as infected spots or blisters on the skin, or larger areas of redness and warmth, known as cellulitis.
TREAT ALL FAMILY MEMBERS
Because of the time delay between getting exposed to scabies, and developing any signs or symptoms, it is crucial that when treating scabies all family members including any sexual contacts get treated on the same day.
There are a variety of "scabicides" (such a permethrin or malathion) available on prescription which kill the mite, but they do need careful application. They should be applied to the entire body and scalp, with extra care taken to get into the cracks between fingers and toes, and underneath nails. The treatment needs to be left on overnight, and repeated 7-10 days later to prevent re-infestation. For some people, treatment will be required several times over a month before it is effective.
As well as treating the body, it is crucial that all bedding and clothing be "hot-washed" or hung out in the sun to kill any lingering mites. Items that can't be washed can be placed in plastic bags for 72 hours with the same effect, and furnishings and carpets should be vacuumed.
For more information, visit www.dermnetnz.org.
Dr Cathy Stephenson is a GP and medical examiner.