What Is Scabies?

Human scabies is a skin condition caused by infestations of mites. Once diagnosed, the patient will experience itchiness and inflammatory changes on the skin. It is highly contagious and can be transmitted to close contacts very quickly through skin-to-skin contact or shared items. Globally, up to 200 million people will suffer from scabies. Although less common in Australia, less developed communities are at a higher risk of scabies. For example, up to 50% of children and 25% of adults from the Northern Territory's indigenous community will face this condition at some point in their lives.

What Causes Scabies?

The infestation of microscopic insects causes scabies. The bug is called itch mites or medically known as "Sarcoptes scabiei ". After mating, female mite(s) will burrow through the epidermis or the skin lining, where they will begin to lay eggs for their whole life (1-2 months). Within 2 weeks, these eggs develop into adults and usually live between 4-6 weeks. Once infected, symptoms will begin to appear around 3-6 weeks later.

Immune Reaction

During this process, by-products from the scabies mites (e.g. faeces, dead bugs, eggs, etc.) will begin to collect under the body's skin. The build-up of these by-products will cause the body to react abnormally (also known as immediate or delayed hypersensitivity reaction). These reactions occur due to an overreaction of the immune system when a foreign substance enters the body. For scabies, this will cause redness, itchiness and other symptoms detailed below. A similar type of reaction can be seen in those with hay fever due to pollen and pollutants.

Classical vs Crusted Scabies

There are 2 main presentations of scabies: classical and crusted. Whilst they are both caused by the same mite infestation, the crusted variant tends to be more severe. The main difference between these two presentations is that roughly 5-15 mites infest those with classical scabies compared to up to 2 million for those with crusted scabies. In many situations, those who develop crusted scabies already have pre-existing immune deficiencies (e.g. HIV, cancer, etc.).

How Do You Get Scabies?

Scabies Transmission

The transmission of scabies occurs most frequently in children and older adults, particularly in more tropical and busy areas (e.g. hospitals, nursing homes, schools, etc.). Interestingly, scabies can also be transmitted from animal to animal, but not directly from animal to humans. The main transmission paths are person-to-person contact or through shared objects (e.g. clothes, towels, etc.).

Is scabies contagious?

Infections are highly contagious and can occur rapidly and may only need 20 minutes of close contact to occur. Those living in the same household, particularly in overcrowded environments, are at a higher risk.

Scabies Symptoms

The symptoms from a scabies infection are mainly because of the host's allergic reaction to mite's infestation. The appearance of inflammatory papules (red bumps on the skin) and accompanying itchiness are typical symptoms associated with scabies. Other more general symptoms include the urge to itch/scratch, eczema and skin infection. In many cases, these features won't begin to occur until 6 weeks after the mite has entered the body.

How to Identify Scabies

This condition can be further broken down into 'classical' and 'crusted' scabies. Despite the similarity in symptoms, they have some subtle differences, which can be highlighted in the table below.

Classical Scabies	Crusted scabies
Papules, red spots or rashes throughout the body, especially the stomach, waist, genitals, breasts and webbing between the fingers and toes Extreme itchiness, particularly at nighttime	Scaly and crusty plaques in various locations on the body. In more severe cases, deep fissures or cracked skin can develop. Bony areas, such as the elbow and knuckles, can produce more brown and yellow plaques. Mild or no itchiness

Complications

One of the most common complications of scabies is developing secondary bacterial infections (e.g. streptococcus pyogenes, staphylococcus aureus, etc.). Due to the itchiness of the condition, those infested can begin to scratch excessively, leading to skin sores. If not managed appropriately, these sores can rarely lead to bacterial infections and more severe complications, including:

Cellulitis
Kidney failure
Acute Rheumatic fever
Death

To prevent further risk of complications, you should see a GP as soon as possible.

Scabies Diagnosis and Tests

Typically, a diagnosis can be made after a thorough assessment by a GP. They will be able to determine the presence of scabies based on your symptoms and signs. GPs will look out for specific signs of scabies, including the location of the scabies rash or plaques and the severity of the itchiness and whether anyone else in the household has symptoms. For more evidence of mite infestations, a skin sample can also be examined under a microscope. Alternatively, a handheld dermatoscope can also be directly used on patients to inspect the skin thoroughly. Features of mites, eggs or faeces can be identified using the devices' ability to magnify the area.

Scabies Treatment

Treatment for scabies will vary depending on the affected person's age, severity, location of the symptoms and the presence of any bacterial infections. As scabies is highly contagious, close contacts and household members will also require treatment to prevent re-infestations. GPs play a crucial role for providing strategies regarding scabies prevention.

How to Get Rid of Scabies

For classical scabies, most doctors will initially prescribe specific creams (e.g. Permethrin 5%, Crotamiton, etc.) depending on your situation. Usually, these creams are applied throughout the whole body (except the head and neck) and washed off after approximately 8 hours. Although one application is usually enough, additional doses or alternative treatments may be recommended depending on the persistence of the symptoms. Close contacts will also have to undergo the same treatment. However, those with bacterial infections and crusted scabies may require further treatment. As these more serious conditions can lead to more severe complications, seeking a medical opinion is crucial for receiving appropriate treatment. Examples of additional treatments include scabies medication, antibiotics and hospital admission.

Scabies Recovery

Most people with scabies will fully recover from itchiness and skin irritation with the correct treatment. However, those in overpopulated or in less hygienic environments can experience re-infestations. On the other hand, those with crusted scabies can be difficult to manage and may need multiple treatments.

References

Hardy, M., Engelman, D., & Steer, A. (2017). Scabies: a clinical update. Australian family physician, 46(5), 264-268.
Johnston, G., & Sladden, M. (2005). Scabies: diagnosis and treatment. BMJ (Clinical research ed.), 331(7517), 619–622. https://doi.org/10.1136/bmj.331.7517.619
Salavastru, C. M., Chosidow, O., Boffa, M. J., Janier, M., & Tiplica, G. S. (2017). European guideline for the management of scabies. Journal of the European Academy of Dermatology and Venereology, 31(8), 1248-1253.

Scabies – Symptoms, Diagnosis, and Treatment