Itch Mite
Several biological races of Sarcoptes scabiei (DeGeer), Sarcoptidae, ASTIGMATA


DESCRIPTION

Adult -- Though there are several biological races of the itch mite, they cannot be differentiated on the basis of appearance. The adult has a round body 0.3 to 0.5 mm in diameter with four pairs of short legs. The first two pairs of legs in the female and pairs one, two and four in the male have long, stalked, terminal suckers. The other pairs of legs terminate with long, ship-like setae.

Egg -- Each tiny, oval egg is about 0.2 mm long.

Larva -- The white, circular larva has only three pairs of legs. Too small to be seen with the naked eye, this parasitic stage is about 0.2 mm in diameter.

Nymph -- Also white and circular, the nymph has four pairs of legs. It is only slightly smaller than the adult.


BIOLOGY

Distribution -- Itch mites can occur anywhere a host is present. Infestations tend to be most common during cool weather months.

Hosts -- Each biological race of the itch mite attacks a specific host. Mammals subject to infestation by races of this parasite include horses, cattle, hogs, dogs, rabbits, sheep, and man. Mites transferred from one type of animal to another cannot survive and soon die, although they may cause some annoyance before dying.

Damage -- Itch mites are the cause of mange. They usually first establish themselves on the least hairy parts of their host's body. On man, such infestations are likely to develop between fingers, behind knees, etc.,; on animals, the mites congregate around the eyes, ears, and nose, on the inner surface of the thighs, etc. Once established, however, the mites may spread to all parts of the body.

Life History -- As a rule, itch mites spend their entire life cycle on the host. However, they can survive in moist bedding without a host for 4 to 6 weeks. In such cases, temperature is a critical factor affecting survival because the mites are most suited to the normal temperature of their host's body.

Unfertilized female adults burrow in thickened, calloused skin. They then return to the surface and mate. A few hours later, fertilized females begin laying eggs along tunnels burrowed in the skin. Egg deposition continues at 2- to 3-day intervals for a month or more. Each female deposits about 10 to 25 eggs every two weeks; however, fewer than 10% of the eggs mature into adults.

Eggs incubate 3 to 5 days before the microscopic larvae emerge. These 6-legged immatures either remain in the skin burrows or enter hair follicles where they develop 2 or 3 days before molting into nymphs. As 8-legged nymphs, the mites feed for 4 to 6 days and develop through 2 instars. These nymphs then become adults and the life cycle is repeated. A new generation can be produced about every two weeks.


CONTROL

Domesticated animals, except those only a few months old, can be dipped or sprayed to control itch mites (mange.). Treatment of infestations is best done in early fall since mite populations tend to increase during months of cool weather. Newly treated animals should be sheltered from cold weather and sunlight to prevent chilling and blistering. In addition to animals, stables and shelters may also need to be disinfested with steam, boiling water or chemicals. Diagnosis and treatment of human scabies should be done under the supervision of trained medical personnel.