House dust mites


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House dust mites
House dust mite

House dust mite

Systematics
Subclass : Mites (acari)
Superordinate : Acariformes
Order : Sarcoptiformes
Subordination : Oribatida
Family : Pyroglyphidae
Genre : House dust mites
Scientific name
Dermatophagoides
Bogdanov , 1864

The house dust mite ( Dermatophagoides ) are a genus of mites belonging to the arachnids include. The most common house dust mite species are Dermatophagoides pteronyssinus and Dermatophagoides farinae . Another species widespread in Europe , Dermatophagoides microceras , has so far been confused with farinae .

To date, 49 species of the Pyroglyphidae family have been identified worldwide, 13 of which live in house dust, only six or seven more frequently. But there are other types of mites that can live in houses, particularly numerous in the tropics. The original habitat of the house dust mites are bird nests, from there they have been transferred to human dwellings and have been spread around the world.

features

Dust mites are about 0.1 to 0.5 mm in size and white. Their bodies have hair-like bristles. They differ from other mite species that live in houses in Central and Northern Europe in their finely striped body shell ( cuticula ) (in the species of the Glycyphagidae family it is smooth or covered with papillae, in the Tarsonemidae with overlapping plates). They differ from the genus Euroglyphus (with the species Euroglyphus maynei ), which also lives in houses, in the length of two bristles on the trunk (idiosoma) and the lack of a sclerotized plate (tegmen) on its front end.

Overview

The scientific name Dermatophagoides means 'skin eater'. Dust mites feed on the flakes of skin that have fallen off, of which humans lose around 0.5 to 1 gram per day. Older, moist skin flakes are preferred to freshly fallen ones. There are contradicting statements as to whether scales infested with molds of the genus Aspergillus are preferred. In one study, the fungus reduced the mites' lifespan and reproduction. This effect was reversed in the long term, however, and mite populations without contact with the fungus could not survive in the long term. Presumably essential nutrients are provided by the fungus .

Life cycle and reproduction

House dust mites have separate sexes, with the males being significantly smaller than the females (females reach a live weight of 5.8 micrograms, males only 3.5). After the copula, the females lay the eggs, but not as a clutch, but individually over a long period of time. The lifespan of females is heavily dependent on temperature and humidity and also varies somewhat from species to species, it ranges from around 30 to 100 days. During this time they lay between 40 and 80 eggs. A deutonymph (also known as a larva) hatches from the eggs. This transforms into a tritonymph, from which the adult animals emerge (two larval stages). Each conversion step is associated with a period of rest of different length, during which the animals are considerably more resistant to adverse environmental conditions. The entire life cycle from egg to sex animal is very variable, it lasts about 30 to 50 days under favorable conditions, but can be extended to 120 days at low temperatures. Animals ready to mate can be found through sexual pheromones . In addition, the animals form aggregations that are brought together by another pheromone.

Way of life and habitat

House dust mites are found almost exclusively in human dwellings; they usually cannot survive outdoors. There is little information about outdoor life, e.g. B. Occurrence in bird nests. Dwellings are being repopulated by mites that are carried in clothing. Most of the dust mites are in bed. There the mattress and the duvet are equally affected. Upholstered furniture is also found; there are usually only a few house dust mites in carpets. High population densities can also occur in other substrates such as older books. The highest concentration is found in mattresses and pillows, because there are plenty of flakes of skin as food and a lot of moisture: A sleeping person excretes around 40 g of water per hour with the breath and in sweat, estimated transition rates for skin to mattress are: 180– 220 g / per night and person, for skin to pillow 15–20 g / per night and person.

Air humidity and temperature are essential factors for the frequency of mites in houses. There is hardly any food shortage due to the extremely low requirement (no increased mite infestation in people with psoriasis ). The tiny creatures also take up little space: if flakes of skin have penetrated the inside of foam mattresses, the animals can easily live in them. Population- reducing factors: Attracted by the sexual attractant , the mite-eating mite Cheyletus can appear. Another natural enemy is the book scorpion . Also silverfish feed on, among others, dust mites. In the normal habitat of house dust mites, none of these species play a role because they are far too rare for a population control.

Effect of humidity on survival

The optimal conditions of the two common species Dermatophagoides pteronyssinus and Dermatophagoides farinae are somewhat different. D. farinae prefers somewhat warmer places and can withstand somewhat higher drought (optimum at 25–30 ° C and 70–75% relative humidity, compared to 15–20 ° C and 75–80% relative humidity in D. pteronyssinus ). This species is therefore more common in many parts of the USA - therefore occasionally called "American house dust mite", while its sister species z. B. dominated in cool and damp England. However, both species regularly occur together and, depending on the habitat, one or the other can dominate anywhere. Both species need a relative humidity of 73% or higher to live. You can then absorb contact water or water vapor from the environment. However, due to the large surface they also lose a lot of water. They cannot survive long in areas below 50% relative humidity and also show reduced reproduction and vitality above this. For a long time it has therefore seemed plausible to reduce the mite density by drying out. However, there is plenty of evidence that even very short periods of high humidity of around three hours a day are sufficient for the animals to live permanently. If scientifically strict standards are applied, no method of direct mite control (neither dehydration nor supposedly mite-safe mattresses or the like) has an effect on the suffering of asthmatics. However, according to numerous studies, the mite density and the relative humidity are closely correlated. The humidity of the ambient air is in any case completely sufficient for the species to survive, so control by ventilation is not possible. There are indications that a reduction in air humidity through technical devices is effective, but only if it takes place over very long periods of time without a break. The relative humidity in winter is presumably decisive for the mite density.

Temperatures and humidity above the optimal range cause a population decrease. Heating (a few minutes to 50 ° C or longer time to 40 ° C) can reduce the mite density and has been suggested as a control method.

In the winter months, the drying out of the air due to heating should worsen the living conditions for house dust mites. In fact, it has been observed that the mite density is significantly higher in summer and autumn than in winter. The animals can often reproduce slowly under the suboptimal conditions and otherwise survive in one of the more resistant permanent stages. Mattresses that are regularly moistened by the sleeper also offer a possible refuge. The conditions for survival are not optimal while the sleeper is still in bed, because the body heat causes the relative humidity to drop.

According to popular opinion, mites do not have favorable living conditions at over 1200 meters, according to other statements at over 1700 meters. Staying in high mountains can therefore provide relief for allergy sufferers. However, a study by the University of Amsterdam in 2010 found that staying at high altitude helps all people with asthmatic symptoms, regardless of whether they are induced by an allergy to mite allergens or not.

Allergenic effect

The mites' allergy-triggering factors are their faeces, eggs and mite remains, including the main allergens Der p 1 , Der p 2 and Der p 23 in the case of the European dust mite, as well as Der f 1 and Eur m 1 . These substances are distributed as fine dust (particle size: approx. 35 µm), are inhaled and can cause allergies , the house dust allergies. Four species are known to cause allergies , in particular D. pteronyssinus , but also D. farinae , D. microceras and D. siboney . About 10% of the population and 90% of asthmatics are allergic to house dust mites or household storage mites (collectively referred to as domestic mites ). In addition to the close association with asthma, house dust mites are also the cause of year-round (perennial) allergic rhinitis . The usual therapy options (removal of the allergen) and the use of special bedding and dust protection have so far proven to be ineffective. Although the methods that have an influence on the indoor climate (lowering the temperature, lowering the air humidity) only reduce the population, the reduced exposure can already have positive effects on the course of the disease. Immunotherapy (by subcutaneous injection and sublingual tablets) is now considered to be a working therapeutic approach for patients with severe symptoms.

According to laboratory findings, a house dust mite produces around 20 globules of feces per day (6 to 40). One gram of house dust can contain more than 250,000 such globules.

Numerous allergenic components of the mite faeces have now been identified, the most important allergens being some of the mite digestive enzymes.

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Individual evidence

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literature

  • Peter Brookesmith: Little monsters: the secret world of tiny living things . Gondrom Verlag, 1999, ISBN 3-8112-1735-6 , pp. 122-128.
  • PC Gøtzsche, C. Hammarquist, M. Burr: House dust mite control measures in the management of asthma: meta-analysis. In: Br Med J. 317, 1998, pp. 1105-1115.
  • David Crowther, Jane Horwood, Nick Baker (The Martin Center, Cambridge University), David Thomson (Medical Entomology Center, Cambridge), Stephen Pretlove (School of Construction, South Bank University), Ian Ridley, Tadj Oreszczyn (The Bartlett, University College London): House Dust Mites and the Built Environment: A Literature Review. EPSRC project “A Hygrothermal Model for Predicting House-Dust Mite Response to Environmental Conditions in Dwellings”. First interim report. 2000.

Web links

  • Pyroglyphidae in the National Library of Medicine, Medical Subject Headings (accessed August 31, 2010)