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What is scabies?
Scabies is a common contagious skin condition. About 300 million people of all ages and walks of life are affected around the world.  Outbreaks in school-aged children are common.
Scabies is caused by the tiny parasitic mite Sarcoptes scabiei. It cannot be seen with the naked eye and is passed on through close physical contact, especially skin-to-skin contact. Less commonly, long-term contact with an infested person's bedding or clothes can also cause scabies.
Scabies normally causes severe itching and rash. Small burrows can often be identified in the skin. Scabies is treatable using prescription medicine. Further exposure and spread can be prevented using good hygiene measures. If left untreated, scabies can spread rapidly throughout a community.
Signs and symptoms
The first signs of scabies can take up to four weeks to appear. If you have been exposed to scabies in the past, the signs will appear more quickly, within one to 4 days, as the immune system has a quicker reaction to a previous infestation.
The first sign of scabies is typically an intense itch, especially at night or after a hot shower. This is a reaction of the immune system to the burrowing mites. The skin will typically appear reddish. A close look at the itchy area may reveal the mite burrows, appearing as short, silvery-grey and raised tracks. These tracks can look straight or squiggly. You may also notice small itchy lumps (nodules) on your skin that look like pimples or blisters.
Scabies most commonly shows up in skin creases and folds, including:
- Between the toes or fingers;
- The groin area and genitals;
- Soles of feet, and;
In infants and very young children, scabies tends to appear on the:
- Head, face and neck;
- Palms of the hands, and;
- Soles of the feet.
The cause of scabies is a microscopic mite called Sarcoptes scabiei. These mites and their eggs survive on clothes or bedding for one to 3 days. The scabies mite cannot fly or jump; it moves between people, mostly through direct physical contact. Forms of close contact, such as parents holding or hugging their children, can pass on the mite. Scabies can also be a sexually-transmitted disease (STD). In rare cases, scabies may also be transmitted without direct contact through shared household items. The scabies mite cannot carry other diseases from one human to another.
Mites meet and mate on the skin. After mating, the male dies and the female digs a burrow under the skin's surface to lay the eggs. A single female can lay one to 3 eggs per day for several weeks. The eggs hatch within three to 4 days. After hatching, the new mites dig back up to the skin's surface. They mature on the skin within ten to 15 days and the cycle starts again.
Risk factors for scabies include:
- Age - being a young or school-aged child;
- Weak immune system;
- Crowded living conditions;
- Poor hygiene, and;
- Physical or sexual contact with someone with scabies.
Methods for diagnosis
Most of the time the diagnosis is made by a clinical assessment. However, scabies can sometimes be tricky to diagnose as other skin conditions, such as eczema, can often mimic a scabies infestation. Once your doctor suspects scabies, there are two common tests they may wish to perform to confirm the diagnosis.
Visual microscope examination
Your doctor will take a scraping of your skin and examine it under a microscope to look for the mites, eggs or mite faeces.
Burrow ink test
Your doctor will mark an area of skin with a marker pen or a few drops of ink, then wipe the area off with a little alcohol. If mite burrows are present, some ink seeps into the mite burrows and they appear as short dark lines.
It is important to note that mites often do not show up on these tests. Rarely, your doctor may wish to perform additional tests, such as histopathology. Your doctor may recommend a treatment even when they find no positive evidence of scabies.
Types of treatment
Scabies can be difficult to clear without a full course of treatment prescribed by your doctor. The most common treatment option is the permethrin cream. If an alternative treatment is required, benzyl benzoate emulsion is generally used. A treatment course may last several weeks, until no eggs or mites remain. Steroid creams and antihistamines are also sometimes prescribed to help calm the inflammation and itch.
For more complicated types of scabies, different treatment options may be required as follows:
Serious infestations and crusted scabies
For serious or long-term cases of scabies, your doctor may prescribe ivermectin pills. This medication is also used in patients with a weakened immune system.
Treatment of associated bacterial infections
Scabies can allow for bacteria to enter the skin and cause associated bacterial skin infections. These will need additional treatment with antibiotics.
Highly irritating as it may be, scabies is normally not a serious or life-threatening condition. However, in a person whose immune system is weakened by factors such as old age, serious illness or malnutrition, scabies can sometimes develop into more severe forms. In addition, scratching the itching skin can lead to secondary infections.
When the immune system is too weak to fight a scabies infestation, the mites can reproduce more quickly. The mites can spread to all areas of the body, numbering in their thousands within an affected area. This causes the skin to thicken and take on a crusty, scaly appearance.
A case of crusted scabies is more difficult to correctly diagnose and treat than regular scabies. It is also highly contagious, due to the large number of mites on the skin.
In a small number of cases, especially in children and young adults, reddish-brown nodules can appear. These are non-infectious small growths or lumps of tissue, located particularly around the pelvis and thighs. Nodular scabies can persist for many months, even after the mites have been successfully treated. It is thought that they are the result of a person having a particularly sensitive immune system, which is still reacting to the scabies even after it has been treated.
Scratching the itchy skin can break the skin and increase the risk of developing a bacterial infection, such as impetigo.
If you have an existing skin condition, you may find that it becomes worse during scabies. The situation should return to normal once the scabies is successfully treated.
Treatments for scabies are generally effective at clearing the mites from the skin. However, you may still continue to feel itchy for several weeks after treatment. This can be because the inflammation caused by the mites requires a longer period of time to completely disappear. There are creams available to help with the itching.
Not all courses of treatments are successful; you may find new burrows and bite marks, indicating that some mites have survived, or a reinfection has occurred.
You can prevent catching scabies by practicing good hygiene measures, including:
- Cutting and cleaning fingernails;
- Avoiding ongoing physical contact with people who have scabies;
- Washing clothing and bedding thoroughly with hot, soapy water, then drying them with high heat;
- Thorough vacuuming of carpets and other surfaces, and disposing of the vacuum bag with care, and;
- Treating all household members and other close contacts at the same time.