Scabies
An intensely itchy skin condition

Scabies, also known as the seven year itch, is a skin disease caused by the human itch mite. The adult female burrows through the skin and lays eggs resulting in complaints of persistent itching and a rash. A superimposed bacterial infection can worsen the condition. A severe form of scabies called crusted or Norwegian scabies can occur in some people with a compromised immune system.

Though scabies has a worldwide occurrence, the highest incidence is found in places with a hot tropical climate and its spread is aided by overcrowding. About 200 million cases of scabies are reported each year.

What causes Scabies

Scabies is caused by the human itch mite, Sarcoptes scabiei hominis. It is transmitted by prolonged skin-to-skin contact and can spread to household and sexual contacts of the infested person. Transmission can occur even when the infested person has no symptoms. Contact with personal items of a person may not cause spread unless it’s a case of crusted or Norwegian scabies. Animals are unlikely to transmit human scabies.

The Italian biologists Giovanni Cosimo Bonomo and Diacinto Cestoni showed in the 17th century that scabies is caused by Sarcoptes scabiei. This discovery of the itch mite in 1687 marked scabies as the first disease of humans with a known microscopic causative agent.

Image: Sarcoptes scabiei or scabies mite. Electron micrograph.

Where is Scabies found

Scabies is found worldwide and more commonly in hot tropical climates seen in parts of Africa, Central and South America, Southeast Asia and Australia. Factors like poverty, overcrowding, and inaccessible healthcare lead to increase in incidence of the disease.

Scabies is one of the three most common skin disorders in children, along with ringworm and bacterial skin infections It affects about 200 million people or 2.8% of the world population.

 

Image: Prevalence of scabies. Few countries have data.

What are the symptoms of Scabies

Children and elderly are more commonly affected by scabies. A person who is infested for the first time may not have any complaints for about 2-6 months while a person who has been affected before can show symptoms within a few days. Symptoms appear due to hypersensitivity (an “allergic reaction”) to the mite and its faeces.

The characteristic symptoms of a scabies infection include intense itching that is worse at night and superficial burrows. The superficial burrows of scabies usually occur in the area of the finger webs, feet, ventral wrists, elbows, back, buttocks, and external genitals.

In most people, the trails of the burrowing mites are linear or S-shaped tracks in the skin often accompanied by rows of small, pimple-like mosquito or insect bites. These burrows can be difficult to find since only about 10-15 mites are present in a person. Vesicles filled with clear fluid may also be seen. Persistent scratching due to an intense itch can lead to superimposed bacterial infection. If untreated, this can lead to entry of bacteria into the blood and damage to the heart and kidneys in some individuals.

Photo: Scabies burrow. The large scaly patch at the left is due to scratching. The scabies mite traveled toward the upper right and can be seen at the end of the burrow.

How can Scabies be prevented

Avoid skin-to-skin contact with an infested person and refrain from using their personal items. If someone in the household is affected, all members are treated in order to prevent spread. Scabies mites usually do not survive for more than 2-3 days away from human contact.

As with lice, a latex condom is ineffective against scabies transmission during intercourse, because mites typically migrate from one individual to the next at sites other than the sex organs.

Healthcare workers are at risk of contracting scabies from patients, because they may be in extended contact with them.

How is Scabies diagnosed

Diagnosis is mostly based on clinical findings of an itchy rash with burrows. Examination under a microscope may reveal mites, eggs or their faeces. A black dot at the end of a burrow may indicate the presence of a mite. Sometimes a skin scraping may be taken and visualised under a microscope.

How is Scabies treated

It is imperative to treat all people who have had prolonged skin-to-skin or sexual contact with the infested person. Everyone should be treated at the same time to prevent recurrence. Scabies mites don’t survive for more than 2-3 days in the absence of human contact. So, all clothes, bedding and towels used in the last 3 days by the infested person, their household and sexual contacts should be washed in hot water. Non-washable items should be dry-cleaned or sealed in plastic bags for at least 3 days.

Medications for scabies (scabicides) kill the mites. The itching may persist for a couple of weeks even after full treatment since it occurs due to an allergic reaction. A doctor’s advice should always be taken when it comes to application of anti-scabies medication and it is important to strictly follow the instructions. Most medicines are in the form of a lotion or cream (eg: permethrin, benzyl benzoate, sulphur ointment, crotamiton) and need to be applied from neck down to the toes. In infants and small children, head and neck can also be affected and the medication should also be applied on those regions. Wash the body only after the recommended time for that product is over and wear clean clothes after that. More than one application may be required. Ivermectin is an oral medicine that is effective against scabies mite.

Not all medicines are considered safe for administration in children, pregnant women and nursing mothers. Therefore, a doctor’s advice is very important. Antibiotics may be required in case a superimposed bacterial infection has occurred.

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