Sarcoptes scabiei or the itch mite is a parasitic mite (an arthropod)
that burrows into skin and causes scabies. The mite is found in all
parts of the world. Humans are not the only mammals that can become
infected. Other mammals, such as wild and domesticated dogs and cats
(in which it is one cause of mange) as well as ungulates, wild boars,
bovids, wombats, koalas, and great apes are affected.
Human scabies sarcopte seen under an optical microscope (x20)
The discovery of the itch mite in 1687 marked scabies as the first
disease of humans with a known cause. The Italian biologist
Diacinto Cestoni showed in the 18th century that scabies is caused by
Sarcoptes scabiei, variety hominis. The disease produces
intense, itchy skin rashes when the impregnated female tunnels into
the stratum corneum of the skin and deposits eggs in the burrow. The
larvae, which hatch in three to 10 days, move about on the skin, moult
into a nymphal stage, and then mature into adult mites. The adult
mites live three to four weeks in the host's skin.
1 Clinical significance
4 See also
The action of the mites moving within the skin and on the skin itself
produces an intense itch that may resemble an allergic reaction in
appearance. A delayed type IV hypersensitivity reaction to the mites,
their eggs, or scybala (packets of feces) occurs approximately 30 days
after infestation. The presence of the eggs produces a massive
allergic response that, in turn, produces more itching. Individuals
who already are sensitized from a prior infestation can develop
symptoms within hours.
Sarcoptes is a genus of skin parasites, and part of the larger family
of mites collectively known as "scab mites". They are also related to
the scab mite Psoroptes, also a mite that infests the skin of domestic
animals. Sarcoptic mange affects domestic animals and similar
infestations in domestic fowls causes the disease known as "scaly
leg". The effects of S. scabiei are the most well-known, causing
"scabies", or "the itch". The adult female mite, having been
fertilized, burrows into the skin (usually at the hands or wrists, but
other parts of the body may also be affected), and lays its eggs.
The burrowing is carried out using the mouth parts and special cutting
surfaces on the front legs. While these are being used, the mite
anchors itself with suckers on its feet. Eggs are laid in small
numbers as the mite burrows, and, as these hatch, six-legged larvae
climb out on to the skin and search for hair follicles, where they
feed and moult (discard old cuticles to grow). In the hair follicles,
the larvae show the first nymphal stages, with eight legs.
In the nymphal stages, the creature feeds and moults, and if male,
gives rise to the adult. In the case of females, another moult occurs
before adulthood. The female has more moults than a male, so takes
longer—17 days compared to 9 to 11 days for a male—to reach
adulthood. The female is about twice the size of the male.
Although the life-cycle is only about two weeks, individual patients
are seldom found to have more than about a dozen mites on them. Even
so, this number can cause agonising itching, especially at night, and
severe damage to the skin often comes as a result of scratching, in
particular by the introduction of infective bacteria, which may lead
to impetigo or eczema.
Video of the S. scabiei mite
Video of the S. scabiei mite
The eggs are laid by the female at a rate of about two to three eggs a
day for about two months. About 2% of the British population is
thought to be infected with these mites, which take about 25 minutes
to an hour to burrow into the skin.
The best conditions in which to harbor S. scabiei is in areas with
frequent skin-to-skin contact, such as the hands and wrists, as the
mites are transmitted by skin contact with carriers, and they very
easily spread. Infestations of S. scabiei are commonly found in pigs.
They significantly depress growth and feeding rate, but usually die
out in around five days in typical farm conditions. However, once in a
herd, the mites are very difficult to eliminate without great measures
Adult scabies mites are spherical, eyeless mites with four pairs of
legs (two pairs in front and two pairs behind). They are
recognizable by their oval, ventrally flattened and dorsally convex
tortoise-like bodies and multiple cuticular spines. No demarcation
into cephalothorax or abdomen occurs, and the mite's surface has folds
covered with short bristles. The front legs end in long, tubular
processes known as suckers, and the hind legs end in long bristles.
The male has suckers on all legs except the third pair, which
distinguishes it from the female. Females are 0.3–0.45 mm
(0.012–0.018 in) long and 0.25–0.35 mm
(0.0098–0.0138 in) wide, and males are just over half that
The scabies mite
Sarcoptes scabiei var. hominis goes through four
stages in its lifecycle: egg, larva, nymph, and adult.
Upon infesting a human host, the adult female burrows into the stratum
corneum (outermost layer of skin), where she deposits two or three
eggs per day. These oval eggs are 0.1–0.15 mm
(0.0039–0.0059 in) long and hatch as larvae in three to four
days. A female can lay up to 30 eggs, then dies at end of a burrow.
Upon hatching, the six-legged larvae migrate to the skin surface and
then burrow into molting pouches, usually into hair follicles, where
vesicles form (these are shorter and smaller than the adult burrows).
After three to four days, the larvae molt, turning into eight-legged
nymphs. This form molts a second time into slightly larger nymphs,
before a final molt into adult mites. Adult mites then mate when the
male penetrates the molting pouch of the female. Mating occurs only
once, as that one event leaves the female fertile for the rest of her
life (one to two months). The impregnated female then leaves the
molting pouch in search of a suitable location for a permanent burrow.
Once a site is found, the female creates her characteristic S-shaped
burrow, laying eggs in the process. The female will continue
lengthening her burrow and laying eggs for the duration of her
Fly strike in sheep
List of mites associated with cutaneous reactions
List of parasites of humans
^ D. B. Pence; E. Ueckermann (2002). "Sarcoptic mange in wildlife"
(PDF). Scientific and Technical Review of the World Organisation for
Animal Health. 21 (2): 385–98. PMID 11974622.
^ Orkin, M. (25 August 1975). "Today's Scabies". JAMA. 233 (8):
882–85. doi:10.1001/jama.1975.03260080044019. PMID 1173898.
Retrieved 30 November 2012.
^ a b c "Scabies". Laboratory Identification of Parasites of Public
Centers for Disease Control
Centers for Disease Control Division of Parasitic
Diseases. 5 December 2008. Retrieved 9 February 2009.
^ L. Arlian (1989). "Biology, host relations and epidemiology of
Sarcoptes scabiei". Annual Review of Entomology. 34: 139–61.
doi:10.1146/annurev.en.34.010189.001035. PMID 2494934.
Diseases from arthropods and ectoparasitics (B85–B89, 132–134)
Body louse (pediculosis corporis) /
Head louse (head lice infestation)
Crab louse (phthiriasis)
Bed bug (cimicosis)
Dermatobia hominis /
Cordylobia anthropophaga / Cochliomyia
Tunga penetrans (tungiasis)
Acariasis / mange (mites)
House dust mite
House dust mite (house dust mite allergy, oral mite anaphylaxis)
Demodex brevis /
Demodex folliculorum (demodicosis, Demodex mite bite)
Trombicula (trombiculosis, chigger bite)
Sarcoptes scabiei (scabies)
Dermanyssus gallinae (gamasoidosis)
Liponyssoides sanguineus (rickettsialpox)
Linguatula serrata (linguatulosis)
Porocephalus crotali /
Armillifer armillatus (porocephaliasis)