Worldwide, there are approximately 300 million human cases of scabies each year. It is a parasitic infestation of the human itch mite, Sarcoptes scabiei variant hominis. Animals such as dogs, pigs, cats, and horses may acquire the condition; however, different races of the scabies mite causes it in them, and these other forms of mites do not reproduce or cause disease in humans.
The disease affects people of all races, socioeconomic levels, and ages, and it transmits via skin-to-skin contact. The female mite burrows into the skin of humans who acquire the disease, and they lay eggs there. The mite will survive for one or two months as long as she is in contact with human skin, but away from human skin, it will not survive more than a few days.
Male mites do not form burrows in the skin, but they do wander on the surface of the human host. Infestation in humans causes intense itching, and there may be skin lesions which look like pimples. Most cases are classic scabies and involve only 10 to 15 mites on the human.
People who experience contact or exposure to the mite will develop symptoms within a few days or weeks, but they are capable of spreading the disease before they know they have it. More severe cases of the infestation involve several thousand to a couple million mites on the human, and these patients are highly contagious. This severe form of scabies is crusted or Norwegian scabies and requires aggressive medical therapy as well as infection control prevention measures.
The rash and itching of scabies may occur on the webbing between the fingers, wrist, elbow, knee, breasts, shoulder blades, armpit, waist, buttocks, and male genitalia. In small children and infants, the itching and rash may occur on the head, face, neck, palms, and soles of feet.
Groups at risk for Scabies
Several groups of people are at risk for the acquisition of scabies. The infestation occurs in crowded situations where contact with others who have the disease is likely to take place. This may be the case with refugees who leave their country during times of political strife, social upheaval, or war.
It is well known that the occurrence of sexually transmitted diseases rises when there is war, and scabies certainly transmits in this fashion both in heterosexual and homosexual relationships. Scabies infestations occur in nursing homes, residential facilities, extended care facilities, hospitals, and child care centers. Socially disadvantaged people such as those who are homeless are prone to acquire the disease.
Household contacts of people who have scabies are at great risk of the disease as the mites are in clothing, furniture, and towels.
Norwegian scabies may occur in patients with immune system compromise, elderly patients, and debilitated or disabled individuals. In these cases, it is necessary that one vacuum the carpet and furniture in rooms that the patient uses in order to prevent disease transmission to others who live there or visit the home.
Another useful infection control measure is decontamination of bedding, clothing, and towels that the patient uses. This is possible through machine wash in hot water and dry with the hot cycle or dry clean. Since the mites do not survive more than a few days off human skin, another approach is to keep the bedding, clothing, and towels away from the person who has the infestation for several days.
Naturally, people without the infestation should avoid contact with anyone who has it.
Diagnosis and Management
Physicians can diagnose the disease with clinical history, physical examination, and microscopic identification of the mite, eggs of the mite, and feces from the mite. However, since most cases of classic scabies only carry 10 to 15 mites, the microscopic examination may not show any of these findings even though the patient already has the disease.
The medical management of this disease requires a prescription from a physician for the appropriate drug to eliminate the mites from the human. Over-the-counter medications are not sufficient to control the infestation. Several agents are available to treat it, and the choice will depend on the individual patient's condition.
References
Centers for Disease Control. (2010). Parasites—Scabies. Retrieved December 28, 2010.
Olivier Chosidow, “Scabies,” New England Journal of Medicine 354 (2006): 1718-1727.
Michael Koger - Dr. Koger obtained his medical education at Meharry Medical College and specialized in Internal Medicine.
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