Overview

Distribution

Scabies mites have a worldwide distribution. Humans are their primary definitive host. These mites are typically found more frequently in impoverished countries, likely due to lack of sanitation, treatment, and other resources.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); antarctica (Native ); oceanic islands (Native )

Other Geographic Terms: cosmopolitan

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Physical Description

Morphology

Females are 0.30-0.45 mm long and 0.25-0.35 mm wide; males tend to be two-thirds to half that size. The body is oval-shaped, ventrally flattened, and dorsally convex, with the dorsal surfaces covered in setae. There are four pairs of legs, with the two most anterior pairs having cushion-like sucker pads (pulvilli) that are used to hold onto the host's skin. They have an anterior feeding structure called a capitulum and a posterior anus. These mites are blind.

Range length: 0.30 to 0.45 mm.

Other Physical Features: ectothermic ; bilateral symmetry

Sexual Dimorphism: female larger

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Ecology

Habitat

Scabies mites are human skin parasites, burrowing into the upper skin layer, never below the stratum corneum (the outermost layer of skin, consisting of only dead cells). Scabies mites penetrate and burrow into the skin more easily where the skin is thin and are found in highest concentrations there, with 63% of mites found on the hands and wrists, 11% on elbows, 9% on feet and ankles, 12% in genital areas, and 2% in armpits. These mites are not typically found in desert areas. They are most commonly transmitted through skin-to-skin contact and, if not on a host, can only survive for a few days.

Habitat Regions: temperate ; tropical ; polar ; terrestrial

Terrestrial Biomes: tundra ; taiga ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Other Habitat Features: urban ; suburban

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Trophic Strategy

Scabies mites ingest cell liquids and skin cells from their hosts.

Animal Foods: mammals

Primary Diet: carnivore (Eats body fluids)

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Associations

There are many variants of scabies mites which infect different types of hosts. For example, Sarcoptes scabiei var. canus, infects dogs and Sarcoptes scabiei var. Suis infects pigs. In humans, their secretions and excretions, in particular, cause allergic reactions and intense itching, often with a blister-like rash. Secondary bacterial skin infections may be caused from scratching areas of infestation, particularly to individuals with compromised immune systems.

Ecosystem Impact: parasite

Species Used as Host:

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There are no known predators of these human skin parasites.

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Life History and Behavior

Behavior

Some variants of scabies mites are capable of detecting odor and thermal stimuli, enabling them to find a host again quickly should they be removed. They may also be attracted to lipid compounds found on host's skin.

Communication Channels: tactile ; chemical

Perception Channels: infrared/heat ; tactile ; chemical

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Life Cycle

Females deposit 2-3 eggs per day for their entire lives (1-2 months). Eggs are oval and 0.10 to 0.15 mm in length. Eggs hatch into larvae with three pairs of legs within 3-4 days. They go to the surface of the host's skin and tunnel back in, creating short burrows called molting pouches. After another 3-4 days, larvae molt into nymphs with four pairs of legs, and continue to molt until reaching adulthood (determined mainly by size). Nymphs and larvae may be found in molting pouches or hair follicles. Under ideal conditions, 10% of eggs reach adulthood.

  • Bush, A., J. Fernandez, G. Esch, J. Seed. 2001. Parasitism: the diversity and ecology of animal parasites. New York: Cambridge University Press.
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Life Expectancy

Scabies mites that are not attached to a host will die within 2-3 days at 25°C and within 10 minutes at 49°C. Survival when not attached to a host varies depending on temperature and humidity. Expected lifespan of mites on a host is 1-2 months.

Typical lifespan

Status: wild:
1 to 2 months.

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Reproduction

Males burrow into female molting pouches, where mating occurs. Once a male has mated with a female, she will remain fertile and capable of laying eggs for the rest of her life.

Mating System: polygynous

Females lay eggs throughout their lifetime (1-2 months), all along their burrows in their host's skin. They typically lay 2-3 eggs per day. Eggs hatch within 3-4 days. Hosts do not generally feel the effects of infestation for 6 weeks, at which time their bodies react, typically with intense itching, to excretions and secretions from the mites.

Breeding interval: A female scabies mite will mate once in her lifetime.

Breeding season: Scabies mites will lay eggs throughout their lifetimes.

Range number of offspring: 60 to 90.

Range gestation period: 3 to 4 days.

Key Reproductive Features: semelparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing

This species exhibits no parental investment.

Parental Investment: no parental involvement

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Conservation

Conservation Status

The worldwide population size of this species is very large and dispersed. It has not been considered for conservation status by any agency.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

  • IUCN, 2012. "The IUCN Red List of Threatened Species" (On-line). Accessed March 02, 2013 at www.iucnredlist.org.
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Relevance to Humans and Ecosystems

Benefits

This skin parasite is harmful to humans, causing severe dermal allergic reactions. Individuals with compromised immune systems may develop what is known as "Norwegian scabies," in which thick crusts form over the infected skin. Different variations of scabies affect many other animals, including livestock.

Negative Impacts: injures humans (bites or stings, causes disease in humans )

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Research is ongoing to find effective treatments and prevention of scabies mite infections.

Positive Impacts: research and education

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Wikipedia

Sarcoptes scabiei

"Itch mite" redirects here. For other uses, see Itch mite (disambiguation).

Sarcoptes scabiei or the itch mite is a parasitic arthropod that burrows into skin and causes scabies. The mite is cosmopolitan, meaning can be found in all part 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.[1]

The discovery of the itch mite in 1687 marked scabies as the first disease of humans with a known cause.[2] The Italian biologist Diacinto Cestoni showed in the 18th century that scabies is caused by the mite 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.

Clinical significance[edit]

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 fertilised, 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.[citation needed]

The best conditions in which to harbour 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 taken.

Morphology[edit]

Adult scabies mites are spherical, eyeless mites with four pairs of legs (two pairs in front and two pairs behind).[3] They are recognizable by their oval, ventrally flattened and dorsally convex tortoise-like bodies and multiple cuticular spines.[4] 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 size.[3]

Lifecycle[edit]

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 life.[3]

See also[edit]

References[edit]

  1. ^ D. B. Pence & E. Ueckermann (2002). "Sarcoptic mange in wildlife" (PDF). Scientific and Technical Review of the World Organisation for Animal Health 21 (2): 385–398. PMID 11974622. 
  2. ^ Orkin, M. (25 August 1975). "Today's Scabies". JAMA 233 (8): 882–885. doi:10.1001/jama.1975.03260080044019. PMID 1173898. Retrieved 30 November 2012. 
  3. ^ a b c "Scabies". Laboratory Identification of Parasites of Public Health Concern. Centers for Disease Control Division of Parasitic Diseases. 5 December 2008. Retrieved 9 February 2009. 
  4. ^ L. Arlian (1989). "Biology, host relations and epidemiology of Sarcoptes scabiei". Annual Review of Entomology 34: 139–161. doi:10.1146/annurev.en.34.010189.001035. PMID 2494934. 
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