Scabies mite – Sarcoptes scabiei
An Itchy Contagious Parasite That Lives On Skin and Burrows
The scabies mite, Sarcoptes scabiei, comes from a family of parasitic mites that cause scabies, or mange, in humans and animals.
The scabies mite, Sarcoptes scabiei, is also known as the itch mite, or mange mite. Scabies mites live on, and in, the skin—they are parasites. The unpleasant condition caused by the mites is usually called scabies; other names are sarcoptic mange or the seven-year itch.
A person afflicted with sarcoptic mange usually has a number of inflamed, incredibly itchy lesions, typically located in creases and folds in the skin—between fingers, in creases of knees and elbows, and in the groin area—and on the backs of the hands, shoulder blades and buttocks. Typically, the victim scratches causing weeping, scabbing, and sometimes infection. Scabies does not clear up on its own, hence the name seven-year itch.
On close inspection, a lesion that has not scabbed over may appear to be a delicate little trail in the skin—the lesions of sarcoptic mange are actually tiny tunnels in the outer layers of skin created by the burrowing activities of female mites.
Females chew their way through the surface and excavate a tunnel beneath, feeding on skin cells and producing a trail of eggs and fecal pellets. The inflammation and itching typical of a scabies infestation is caused by the body’s response to the activities and fecal debris of mites.
Upon hatching, scabies larvae make their way to the surface where they feed and mature, consuming dead skin cells, skin secretions, fungal spores, and bacteria. Eventually they mate; then the females quickly borrow back into the skin to tunnel and lay eggs. Females live about two months and never return to the skin surface.
Immature mites living on the skin are probably the stage of the parasite that is most easily transferred from person to person. Close contact is required, and scabies is well known for its tendency to spread in crowded conditions such as prisons, army barracks, and overcrowded housing. This association has led many people to believe that people afflicted with scabies are dirty or otherwise socially undesirable. This is incorrect: anyone can catch scabies.
Other species of mites that are visually indistinguishable from Sarcoptes scabiei infect various species of animals, causing mange. They typically infest hairless areas on animals and the lesions often become infected with bacteria. Though these mites will readily transfer to human skin and cause symptoms of scabies, they do not tend to cause ongoing infection when they are not on their preferred host.
Here are some other interesting facts about scabies mites:
- Larvae and eggs are microscopic but the mature females are large enough to be just barely visible at the end of their shallow tunnel. A common way to diagnose scabies is to put a drop of mineral oil on a lesion and then scrape the skin with the edge of a sharp blade. If the scraping is vigorous enough, the specimen obtained will contain eggs, fecal pellets, and the female mite.
- In a few individuals Sarcoptes scabiei mites multiply to huge numbers causing a highly contagious condition called crusted or Norwegian scabies.
- Scabies mites have no respiratory system—they breathe through the skin.
- Mites are not insects but arachnids, related to spiders and scorpions.
Read about other burrowing parasites, the Chigoe Flea, and the Screwworm Fly.
Other topics in Fish and Insects:
Sources:
Garcia, Lynn S. and David A. Bruckner. Diagnostic Medical Parasitology 3rd ed. Washington: ASM Press, 1997.
Knutson, Roger M. Furtive Fauna: A Field Guide to the Creatures Who Live on Us. New York: Penguin Books, 1992.
Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th Ed. Boston: McGraw Hill, 2000.
