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A-Z of Skin: Scabies

When Should I Expect I have Scabies?

  • Recent onset of an itchy rash (weeks to months)
  • Other friends, partners or family members are also itchy
  • Itchy pustules on the hands or feet of young children and infants
  • Development of an itchy rash after contact with someone diagnosed with scabies

What is Scabies?
Scabies is due to infestation with a mite called sarcoptes scabei var hominis. This mite can only live on man; and is different to the mites that cause similar conditions in animals. It is a highly contagious condition that causes an itchy rash, often in several members of the same household. The itchy rash is due to the development of allergy to the mite. This may take a month or more after being first infested or exposed to the scabies mite. Thus people with recent infestation may not be itchy.

How can I Catch Scabies?
Scabies can be caught by close contact (eg. skin to skin) with someone with scabies. This includes childhood games, sharing the same bed, clothing, or even just living in the same house as a person with scabies. Any close physical contact such as nursing, or caring for an individual can spread the mite. Occasionally shared objects such as clothes and bedding can transmit the mite. Mite movement is temperature dependent with the mite almost immobilised below 20 degrees centigrade. Thus the transmission of mites is increased in warm environments such as northern Australian communities.

How is Scabies Dignosed?
Scabies should be suspected in anyone with an unexplained itch of recent onset (weeks to months). Itch due to scabies is often worse at night. You cannot see the mite without magnification. The mite however leaves squiggly burrows in the skin, which are usually less than a centimetre long. These are most commonly found on the hands (particularly between the fingers), wrists and feet. Scrapings from a number of burrows will reveal the mite, eggs or faeces when examined under magnification. Itchy lumps or nodules can occur on the penis and are characteristic of scabies.

Who Should be Treated to Cure Scabies?
All close contacts of a person who has scabies should be treated, to prevent reinfestation and recurrence of the itchy rash. All members of an affected household should be treated, not just those that are itchy, plus anyone else who has been in close physical contact with members of an infested household. In extended families this will include grandparents, uncles, aunts and other relatives who have had significant physical contact with affected people.

Infestations in nursing homes, other institutions and large close-knit communities can be a major logistic challenge to eradicate

How do I Treat Scabies?
All members of the same house should be treated at the same time.

If you are pregnant, or there is a chance you could be pregnant, this should be discussed with your doctor before you use any cream or tablet to treat scabies. Similarly discuss treatment of babies, young infants and the old and frail with your doctor, as special precautions may be required.

Permethrin is the treatment of choice in Australia because of its effectiveness and decreased toxicity. Other treatments such as ivermectin may be considered in severe and complicated cases.

Scabies treatment involves:

  1. Before going to bed apply 5% permethrin (Quellada or Lyclear) to the whole body from the neck down (infants and adults over the age of 55 years should also treat the head and neck). It takes around 30mL’s to cover the average adult. Permethrin is available over the counter at chemists. Make sure the cream is applied to all body parts paying particular attention to the elbows, breasts, groin/genitals, hands and feet (including under the nails). If one burrow is spared then the infestation will persist.
  2. The cream should be left on for at least 8 hours before washing. If you wash your hands during this eight-hour period, reapply cream to the hands.
  3. All bed linen and clothes should then be changed and washed (wash with hot water this kills the mite and its eggs). Dry cleaning, ironing, or hot clothes drying are also effective.
  4. Any clothing or bedding that can’t be washed should be put aside for 7 days before using (e.g. placed in a plastic bag). The mite and eggs will die during this time.
  5. The treatment of all household members (steps 1-4) is often repeated at 7-10 days to maximise chance of eradication of the infestation. This should be discussed with your doctor.

Establish with your doctor if any of your household may have a high mite count. If a member of your household has a very high mite count (known as Norwegian, crusted or hyperinfested scabies), it is possible to be reinfested from the home environment such as lounge suites. Extra cleaning measures will be required in such a situation, and special treatments may be required.

Permethrin cream can sting and irritate, this is normal, but if this is severe, wash off the cream and contact your dermatologist to discuss other options.

Why am I Still Itchy After This Treatment?
There are several reasons why an itch and rash may continue after treatment.

Persistent antigen / memory - The allergic reaction to the mite and its products usually takes several weeks to totally settle even when all the mites have been killed. Nodules (lumps) due to scabies occasionally take up to several months to totally resolve, and can be injected by your dermatologist to speed their disappearance.
You have developed an irritant dermatitis - The treatment for scabies can also irritate the skin. The use of moisturizer (eg. sorbolene and glycerine and emulsifiable oil baths (eg. Alpha keri, QV or Dermaveen bath oil) can help settle this type of itch.

You have been re-infested - Reinfestation with scabies is common if a close contact has not been adequately treated. This is why all household members plus all close physical contacts should be treated at the same time.

You have not eradicated the mite - Rarely, treatment fails to entirely eradicate scabies infestation. You should be re-examined by your dermatologist if your itch fails to progressively settle over a few weeks after treatment of your household.


Acknowledgment
This information is based on a publication of the Australasian College of Dermatologists.
Last Modified October 2001 by Drs Christopher Commens and John R Sullivan.