Scabies
(Mite Infestation · Body Lice)
In this condition factsheet:
The Facts on Scabies
Scabies is caused by a mite (a tiny insect-like organism) that's hardly visible without a microscope. The mite is disc-shaped, pearly-white in colour, with 4 pairs of brown legs, and reaches an adult size that is less then 0.5 mm.
Scabies mites can infest warm and moist folds of skin, such as armpits, buttocks, or groin. They can be found behind the knees, on the inside of elbows and wrists, or between fingers. Scabies usually isn't seen on the scalp or on the palms of hands or the soles of feet. It is possible, however, for young children or people who harbour very large numbers of mites to be susceptible in those areas. Seniors might also find mites at the hairline, neck, temple, and forehead regions.
Scabies is quite a common condition, affecting 200 million people worldwide.
Causes of Scabies
Scabies is a highly contagious condition. If you have close contact with a person infested with the scabies mite, your chances of catching it are fairly high. Crowded living conditions, close body contact (e.g., sleeping in the same bed), even holding hands for a while can easily allow the mite to spread from one person to another.
Since the scabies mite won't live away from a human body for more than a few days, direct contact is a much more likely source of transmission than clothing, bedding, or towels. The mites that cause scabies live specifically on humans–they can't be transmitted to or caught from animals, such as dogs.
A female mite lays 2 to 3 eggs per day, just under the surface of the skin. It takes about 2 weeks for these eggs to develop into larvae and finally adults, after which the adults emerge to the surface of the skin to mate. Once mating is complete, the adults reinvade the skin of their host or another person. The presence of the burrowing adult mite, eggs, and larvae cause a terrible itch. The number of infesting mites averages 10 to 15 but varies depending on the person's hygiene.
There is a severe variant of scabies called Norwegian scabies (crusted scabies). It is usually seen in people with weakened immune systems (such as people with AIDS), or can occur in outbreaks in nursing homes or hospitals. In these cases, the number of infesting mites may be in the millions.
Another form of scabies, called scabies incognito, causes an extensive infestation due to corticosteroids (e.g., betamethasone*, hydrocortisone, desonide) applied to the skin.
Symptoms and Complications of Scabies
Scabies causes an intense itching that's worse at night or after bathing. The itching results from an allergic reaction the body has to the mites' feces or excrement. From 2 to 6 weeks after the initial contact, a person will develop a rash, even on parts of the body that aren't infested. Scratching gives no relief from the itch, but can cause bleeding and open sores that are then susceptible to bacterial infections.
The burrow where the mite lives appears as a slightly raised, greyish-white thread on the skin. The female mites lay their eggs at the closed end of these burrows.
In Norwegian scabies, thick crusts form on the skin. Patches of these crusted areas can be found on the palms, soles, buttocks, and ears. Even the nail beds can be infested and appear crusted and thickened. The number of mites associated with this is particularly high, but the itching isn't as intense as in other infestations.
