How Are Scabies Transmitted?

Itch Mite

Scabies is an itch mite that burrows under the skin of humans as well as animals including cats, dogs, horses and pigs. Human scabies (Sarcoptes scabiei var. hominis) are found worldwide, in "...all races and social classes," according to the Centers for Disease Control and Prevention (CDC). The American Academy of Dermatology estimates that more 300 million cases of scabies infestation occur every year in the world.

Life Cycle

The scabies mite, part of the arthropod class Arachnida, begins life as an egg laid by the female mite that hatches in three or four days. The egg turns into a larva after three or four more days. The larva then molts into a nymph by adding a leg, and with the four legs grows into a larger nymph. The nymph then develops into an adult mite. The CDC states that adult female mites are 0.35 to 0.45 mm long and 0.25 to 0.35 mm wide. The mites are "round, sac-like" and eyeless, according to the CDC, and live under the top layer of the human skin. The female moves along the surface of the skin before burrowing to lay eggs. The complete life cycle of the mite is one to two months.

Breeding

The male mite mates once with the female who then travels over the body to locate a prime area to burrow. The genital and buttocks regions are usual burrowing areas, but the mites may move to any area of the body, including the skin between the fingers or on the wrists. Thousands of female mites may be found on the skin before the burrowing process. In some mite species (Norwegian), this mass will appear as a crusty layer composed of female mites. Two to six weeks are required for tiny mite burrows to be visible to the human eye. Itching and red, raw skin are typically the first symptoms of human infestation.

Transmission

The females attach to the skin using the four anterior legs before they begin to burrow. The female mite is easily transferred to other humans during this time through physical contact, including casual contact such as shaking hands. Female mites can also be transferred on bedding or bath towels from an infected person, although human touch is the most common method of movement, according to the DPDx (CDC's Division of Parasitic Diseases). The Norwegian mite variety may be transferred by sitting on furniture where mites have dropped from a human host. Mites are able to live for two days outside a host.

Outbreaks

Parasitic diseases are tracked by local health departments, and outbreaks of scabies are considered serious. Nursing homes, child care, school and private gyms and hotels are common locations for outbreaks. The mite is contained by cleaning all clothing, and by application of prescription scabicide lotions to delouse persons in an infested household.