Two kinds of mites infest the skin of human beings, but the results of these associations are remarkably different. One frequently causes intense irritation and is a medical and a public health pest, and the other is virtually always inconsequential.
Sarcoptes scabiei var. hominis is a tiny (microscopic) mite that burrows into the skin. The human scabies mite solely infests people and causes a condition known as scabies. Their close relatives that infest non-human animals do not survive long or cause chronic infestations of people.
Scabies mites live in the stratum corneum, the outermost – and non-living - layer of the skin. This infestation affects some people worldwide, and frequently causes intense itching of the skin, but only after the person has been infested for a month or more already. The itching is caused by an allergic reaction to the proteins within or excreted by the mites. The mites, themselves, are usually restricted to small burrows in the skin, and these most commonly occur on the webbing between the fingers and in skin around wrists, but may be found elsewhere on the body.
Scabies mites are mainly acquired by direct and prolonged skin contact with another infested person. On occasion, one or more mites may be deposited on bed linens. These may pose some risk to others, but for just a brief interval (hours or perhaps a day or so). This is a good reason to launder bed linens frequently, particularly in health care facilities, homeless shelters, prisons and hospitality settings.
The diagnosis of scabies is often problematic, particularly in many developed parts of the world where physicians tend not to receive relevant training and also rarely encounter or recognize this condition. Indeed, most ‘diagnoses’ of scabies cases in North America are rendered on subjective or symptomatic bases (the patient complains of itchy skin), and then are treated presumptively. Ideally, a clinician who suspects a scabies infestation will endeavor to find a mite or mite egg in the skin, and confirm this microscopically before prescribing treatment. This may involve a skin scraping, biopsy or yet other procedure that should be performed solely by a medical professional, and the harvested material evaluated microscopically by a parasitologist. Health care providers are encouraged to contact us for guidance and assistance.
In the absence of a genuine mite, the itching may be caused by other kinds of infections, metabolic disorders, dry skin, drug interactions, physical irritation or chemical exposure. When diagnosed objectively and treated appropriately, the patient may be rendered free of the infestation within a day, but the itching may continue for nearly a month, thereafter, because of continued allergic reactions to the dead mites within the skin.
Sarcoptes scabiei - human scabies mite
