What Is Scabies? What Causes Scabies?

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Main Category: Dermatology
Article Date: 28 Feb 2012 - 0:00 PST


Scabies is a contagious skin condition caused by tiny mites called Sarcoptes scabiei. These mites burrow into the skin, then breed and lay their eggs, causing a rash and intense itchiness. Sufferers of scabies rarely know they have the condition until a number of weeks after initial infection; this means scabies infestations can spread quickly.

Scabies is commonly seen as a condition brought about by poor living conditions and lack of personal hygiene, but there is no evidence that suggests this to be true. Scabies can affect anyone and can be treated with certain creams and lotions. There are some groups however that are at greater risk of having the condition.

According to Medilexicon's medical dictionary, scabies is:

1. An eruption due to the mite Sarcoptes scabiei var. hominis; the female of the species burrows into the skin, producing a vesicular eruption with intense pruritus between the fingers, on the male or female genitalia, buttocks, and elsewhere on the trunk and extremities.

2. In animals, scabies or scab is usually applied to cutaneous acariasis in sheep, which may be caused by Sarcoptes, Psoroptes, or Chorioptes.

What are the signs and symptoms of scabies?

A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor, detect. For example, itchiness may be a symptom while a rash may be a sign. Sometimes the signs and symptoms of scabies do not become visible for up to six weeks after contracting the infection.

The primary symptoms of scabies are a skin rash, and intense itching that worsens at night or after a hot shower or bath.

The rash consists of small red spots that look like tiny insect bites (called burrow marks), this rash can be mistaken for other dermatological conditions, for example, eczema. Burrow marks are usually in a small line of four or more and typically appear in the following areas of the body:

• on the elbows
• round the nipples - for women
• near the genitals - for men
• in-between the fingers and toes
• on the wrists

If the rash is scratched, it can become inflamed and the patient may develop crusty sores on the scratched area. Other less common areas where the rash can appear are:

• the axillae (underarm)
• ankles
• buttocks
• genitalia - for women
• groin
• inside the elbow
• knees
• lower leg
• nipples
• shoulders
• soles of the feet
• waist

Children and infants that have contracted scabies can get burrow marks in other areas of their body including:

• the scalp
• the soles of the feet
• the palms of the hands
• the neck
• the head
• the face

What causes scabies?

Scabies occurs when the human body becomes infested with parasitic mites, known as Sarcoptes scabiei. These microscopic creatures were first discovered to cause scabies in the 18th century by Diacinto Cestoni, an Italian biologist.


Sarcoptes scabei

Infestation starts when the female burrows into the skin, the males travel between burrow sites searching for an unfertilized female to mate with. The male then dies and the female starts to lay eggs, which take around four days to hatch.

The hatchlings then surface, and approximately two weeks later mature into adults. The young mites that have matured into females create new burrows by tunneling back into the skin. The ones that mature into males will remain on the surface and begin searching for mates. Unless treated this process will repeat itself indefinitely.

Although the cause of the intense itching experienced by scabies sufferers has not been proven, experts believe it is the patient's immune system responding to the mites' movement, their eggs, their saliva and/or their feces.

How is scabies transmitted?

Scabies is most commonly transmitted through close body contact for an extended period. Holding hands for a while or sexual intercourse are typical examples. Transmission of scabies by hugging or shaking hands is less likely as it is usually too brief.

Scabies mites cannot fly or jump. They can, however, survive a couple of days after leaving the human body, meaning that people sharing clothes or a bed with someone infected are at risk. Transmission by these means is much less common than prolonged physical contact.

Environments that are enclosed, such as nursing homes or schools, pose a greater risk of scabies transmission due to their populations being in close proximity to each other. It is important that the medical staff in these environments possess the training needed to identify scabies symptoms to avoid the infestation spreading.

How is scabies diagnosed?

If someone suspects they have scabies, they can visit their GP/Doctor or GUM (genito-urinary medicine) clinic to be examined. These clinics will either perform or recommend the necessary treatment.

Diagnosis of scabies is typically performed by a doctor assessing the visual signs. In less obvious cases, some tests may need to be performed to eliminate the possibility of the patient having a different skin condition, such as eczema or impetigo.

To confirm that the visual marks on the skin are indeed burrows, ink is rubbed on the area. An alcohol pad is then wiped across this area. If burrows are present, some of the ink remains and will appear as a dark line in the skin. This process is known as an ink test.

Sometimes, instead of ink, a topical tetracycline solution can be used. This solution will glow when under a special light. Interpretation of the ink test can be difficult when the burrows are not obvious to the naked eye or are hidden under scratch marks.

For a more conclusive diagnosis, a doctor would need to find evidence of the scabies mites. To do this a sample of the affected area would need to be procured. This sample would then be searched for the following:

• the mites themselves
• mite eggs
• mite faeces

To find any traces of the above, the skin sample would be set in some potassium hydroxide and examined under a microscope or dermatoscope.

How is scabies treated?

The mites are able to resist hot water and soap and scrubbing the skin does not remove them either. Special creams or lotions have to be applied.

When someone has been diagnosed with scabies it is vital that all members of that person's household and any recent sexual partners be treated as well. This will prevent re-infection and should be done even if the other parties treated are showing no signs or symptoms.

The two most common creams or lotions used to treat scabies are permethrin cream, which is generally the first treatment recommended, and malathion lotion, which is used when permethrin cream has no effect. Both treatments incorporate insecticides capable of killing the scabies mite.

• Permethrin cream - needs to be taken with caution if the patient is younger than 2 years of age or a pregnant woman; a doctor should always be consulted before the cream is used. Side effects can include itching, skin irritation and a stinging or tingly sensation.
• Malathion lotion - although melathion lotion does not have the same effects on pregnant or breastfeeding women as permethrin cream, doctor consultation is still recommended. Side effects can include skin irritation.

It is important to machine wash all clothing, towels and bedding on a high temperature (above 50 degrees C/122 degrees F) as this will kill any mites. Oral antihistamines or steroid creams may be prescribed to help relieve the itchiness.

What are the complications of scabies?

One complication of scabies is a more severe form of the condition called crusted scabies. It is less common and affects people with a reduced immune system, such as:

• women who are pregnant
• people with Down's syndrome
• individuals with neurological disorders
• infants and very young children
• individuals with a condition causing immunodeficiency (HIV or AIDs)
• the elderly
• patients taking steroids for treatment of other conditions
• those having chemotherapy

Having a healthy immune system interferes with the reproductive cycle of scabies mites. If a patient's immune system is weaker than normal, they would be a more suitable breeding ground for the mites. Someone with typical scabies may only have 10-15 mites in their skin, whereas with crusted scabies the number of mites present can be in the thousands or millions.

The mites spread across the host's body, with exception of the face, and lead to the following symptoms:

• thick crusts of skin that can be host to thousands of mites
• scaly rashes
• less itching than regular scabies

The crusts protect the mites to a degree, making the condition much more difficult to treat. Crusted scabies is regularly misdiagnosed as psoriasis. Insecticide creams or ivermectin can be used to treat the condition.

Scabies can worsen existing dermatological conditions such as eczema, which after the scabies is treated should return to normal. Another complication of scabies is the development of a secondary infection like impetigo, which can occur when the skin is scratched excessively, causing it to break and become vulnerable to the infection.





Written by Mike Paddock
Original article date: 28 November 2004
Article updated: 28 February 2012
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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