Scabies is a skin infection primarily characterized by a relentless itch. It is highly contagious and can easily spread through direct skin-to-skin contact.
Scabies is caused by a mite known as Sarcoptes scabei. Sarcoptes is a skin parasite that is part of a larger family of mites known as scab mites. The mites are tiny (less than 0.5 mm in size). The female mites burrow into the outermost layer of the host’s skin and deposit eggs there which may hatch into larvae in three to ten days, and mature in ten to fifteen days. A mite can lay about 40 to 50 eggs in its lifetime. The mites can live in the host’s skin for several weeks.
The movement of the mites on the host’s skin causes an itch as the host’s immune system reacts to the mites. The rash and the itching is the body’s reaction to the mites or their saliva or their feces.
Scabies is contagious but spreads largely through direct skin-to-skin contact with an infected person. It is generally spread through prolonged contact like sharing a bed as opposed to momentary contact like a handshake. It can also spread through sexual intercourse.
In some cases, scabies is spread through contact with towels, bedding and personal items that have been used by a person with scabies. However, this is not a major mode of transmission as mites cannot survive for long durations away from human skin.
Generally, scabies can easily spread among members of a family, or a school class or other groups where people are in constant touch.
The mites are also not found on animals. Thus, it is possible to get these mites only through contact with other humans.
Symptoms usually appear within two to six weeks after getting infested in persons who have not been exposed to scabies earlier. Those who have previously had scabies may start experiencing symptoms within a few days. It is also possible for symptoms to appear after several months.
A major symptom of scabies is intense itching. The itching may get worse at night or because of warmth, for instance, after a hot bath. The itching is quite severe and may possibly begin at one place before spreading to other areas.
Another characteristic symptom of scabies is the appearance of mite tunnels or burrows on the skin. These usually appear in the folds of the skin as thin, fine and silvery lines. They typically occur between fingers, inner surface of wrists, in armpits, around the waist or breasts or male genital area, on the inner elbow, knees, soles of the feet or shoulder blades. In children, the mites are typically found in the scalp, neck, face or soles of the feet.
Usually a rash also appears after itching has started. The rash is typically blotchy and lumpy and can appear anywhere on the body. The rash is sometimes confused with other skin conditions.
Severe itching because of scabies often leads to scratching which in turn, can cause minor skin damage. The damaged skin may also become infected with bacteria. Further, scabies can worsen pre-existing skin conditions like eczema and psoriasis.
It is entirely possible for a person to spread scabies before knowing that he or she is infested since symptoms occur much after infestation.
The scabies rash can usually be diagnosed simply by looking at it. Sometimes, since the rash may look like other skin conditions, a doctor may also look for the mite tunnels or burrows. The burrows are detected by rubbing ink on suspected areas and examining them to see if a burrow-like trail is formed. A portion of dry skin from the affected area may be scraped off and examined under a microscope for the presence of mites or their eggs, which would confirm the diagnosis.
If several members of a family develop itching and rashes, it is possible that they have been infested by the mites and would all have to be treated.
Scabies requires treatment and the mites do not go away on their own. The most common and effective treatment for scabies is application of permethrin cream. It is an insecticide which is usually applied at night and washed off in the morning. It is to be applied all over the skin (from the neck down) leaving no area uncovered so as to prevent mites from remaining in the uncovered spots. Usually one application is considered sufficient since permethrin kills the mites and their eggs. However, sometimes doctors may recommend a second application a few days later as a precautionary measure.
Other treatments include a liquid known as malathion, and sulfur ointments but the most common treatment, by far, is permethrin.
In elderly persons or those with weakened immune systems, the mites may spread all over the body, except the face, in a condition known as crusted scabies. Such hosts may have scaly rashes and crusts of skin with thousands of mites. For such cases, in addition to permethrin, oral ivermectin may also be prescribed.