- House dust mite
House dust mite Scientific classification Kingdom: Animalia Phylum: Arthropoda Class: Arachnida Subclass: Acarina Order: Acariformes Family: Pyroglyphidae Genus: Dermatophagoides Species: D. pteronyssinus Binomial name Dermatophagoides pteronyssinus
The house dust mite (sometimes referred to by allergists as HDM) is a cosmopolitan guest in human habitation. Dust mites feed on organic detritus such as flakes of shed human skin and flourish in the stable environment of dwellings. House dust mites are a common cause of asthma and allergic symptoms worldwide. The mite's gut contains potent digestive enzymes (notably proteases) that persists in their feces and are major inducers of allergic reactions such as wheezing. The mite's exoskeleton can also contribute to allergic reactions. The European house dust mite (Dermatophagoides pteronyssinus) and the American house dust mite (Dermatophagoides farinae) are two different species, but are not necessarily confined to Europe or North America; a third species Euroglyphus maynei also occurs widely.
The body of a house dust mite is just visible against a dark background in normal light. A typical house dust mite measures 0.4 millimetres (0.016 in) in length and 0.25–0.32 millimetre (0.010–0.013 in) in width. Both male and female adult house dust mites are creamy blue and have a rectangular shape. The body of the house dust mite also contains a striated cuticle. Like all acari, house dust mites have eight legs (except 3 pairs in the first instar).
The average life cycle for a male house dust mite is 10 to 19 days. A mated female house dust mite can last up to 70 days, laying 60 to 100 eggs in the last 5 weeks of her life. In a 10-week life span, a house dust mite will produce approximately 2,000 fecal particles and an even larger number of partially digested enzyme-covered dust particles.
Habitat and food
The house dust mite survives in all climates, even at high altitude. House dust mites thrive in the indoor environment provided by homes, specifically in bedrooms and kitchens. Dust mites survive well in mattresses, carpets, furniture and bedding, with figures around 188 animals/g dust. Even in dry climates, house dust mites survive and reproduce easily in bedding (especially in pillows), deriving moisture from humidity in the air.
House dust mites consume minute particles of organic matter. Like all acari, house dust mites have a simple gut; they have no stomach but rather diverticulae, which are sacs or pouches that divert out of hollow organs. Like many decomposer animals, they select food that has been pre-decomposed by fungi.
Asthma and allergies
Allergens produced by house dust mites are among the most common triggers of asthma. There are at least 15 mite allergens which are subdivided into groups. Group 1 and 2 allergens are the most problematic. Group 1 consists of proteins with a catalytic activity, for example Der p 1 (Dermatophagoides pteronyssinus group 1) allergen is a cysteine protease, as is its American counterpart Der f 1 (Dermatophagoides farinae group 1). Group 2 are proteins important for the mite. Proteins from the other groups affect only few patients. Studies have shown the mean attributable fraction of adult asthma due to atopic sensitization was 30% and 18% for sensitization to dust mites. Taken into consideration this could mean as many as 1.2 billion people could have some form of chronic sensitization to dust mites.
The allergy occurs because the immune system of allergy affected individuals, for reasons not fully understood, misinterprets a usually innocuous substance as a disease agent and begins producing a type of antibody against it, called immunoglobulin E (IgE). This is called the 'primary antibody response.' The IgE produced during this response binds to basophils in the bloodstream and to a similar type of cell called mast cells in the tissues. When the person again encounters the allergen, these basophils and mast cells that have bound to IgE release histamine, prostaglandins and leukotrienes, which causes inflammation of the surrounding tissues, resulting in allergic symptoms. Most treatment has relied so far on trying to counteract the released chemicals with anti-histamines, corticosteroids or Salbutamol. Commercial brands of these medications most commonly prescribed to treat Asthma include Ventolin and Seretide.
Newer methods to try to treat house dust mite allergy involve immunotherapy. A safety and tolerability clinical trial (Phase IIa) has been completed with positive results by Cytos Biotechnology using an immunotherapeutic (CYT003-QbG10) for treatment of house dust mite-triggered allergies. The French biopharmaceutical company Stallergenes is developing, via the Stalair Program, sublingual desensitization treatments for house dust mite allergy. The immunotherapy tablet, "Actair", has demonstrated efficacy after 4 months of treatment and the persistence of its therapeutic effect after only one year of treatment. (study VO57.07 conducted in Europe) Stallergenes is now preparing filing NDA in Germany. A phase III pediatric study has been launched.
Typical symptoms of house dust mite allergies are itchiness, sneezing, inflamed or infected eczema, watering/reddening eyes, sneezing repeatedly and frequently; e.g., on waking up sneezing 10 or more times, runny nose and clogging in the lungs.
At present, the best form of treatment for dust mite allergies is avoidance of dust mites and their allergens combined with medication such as anti-histamines, corticosteroids or Salbutamol. The environment of bedding is optimal for most dust mites, and comparative studies have shown that the density of dust mites in mattresses to be on average greater than 2500/gram of dust. Cleaning beds with most vacuum cleaners will not remove dust mite allergens, but instead throw them into the air and increase their volatility. Some polyethylene bedding is beneficial as it makes the environment difficult for the dust mites. This bedding should also be breathable and be able to withstand frequent washing. A home allergen reduction plan has been recognized as being an essential part to the management of asthma symptoms. and therefore all aspects of the home environment should be considered (proper vacuuming, use of air cleaners, etc.). The Asthma and Allergy Foundation of America as well as the Asthma Society of Canada certify products that may be used in a home allergen reduction plan in a Program called Asthma and Allergy Friendly.
Myths and misconceptions
It is commonly believed that the accumulated detritus from dust mites can add significantly to the weight of mattresses and pillows. While it is true that the fecal matter of dust mites will increase over time, there is no scientific evidence for these claims.
Allergy and asthma sufferers are also often advised to avoid feather pillows due to the presumed increased presence of the house dust mite allergen (Der p I). The reverse, however, is true. A 1996 study from the British Medical Journal has shown that polyester fibre pillows contained more than 8 times the total weight of Der p I and 3.57 times more micrograms of Der p I per gram of fine dust than feather pillows.
A simple washing will remove most of the waste matter. Exposure to temperatures over 60 °C (140 °F) for a period of one hour or freezing, exposure to temperatures below 0 °C (32 °F), will typically prove fatal to house dust mites; a relative humidity less than 50% may also be fatal. Ten minutes in a household clothes dryer at lethal temperatures has been shown to be sufficient to kill all the dust mites in bedding. House dust mites reproduce quickly enough that their effect on human health can be significant.
As dust mites like warm, fluffy furniture and materials, they are most likely to be found on beds, couches, carpets, rugs, toys, and curtains. Washing will not completely remove all mites or their droppings, but it will remove at least 90%. It is best to have a carpet free house if dust mites or any house pests are dangerous for a person (e.g., because of their allergy), as flat surfaces are easier to clean and vacuum. If a person is allergic to dust mites, anti-mite mattresses or mattresses which prevent any house pests should be used. Regular cleaning and washing of areas where dust mites thrive is necessary to keep them and their waste to a minimum.
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- ^ Epidemiology of house dust mite allergy. doi:10.1111/j.1398-9995.1991.tb00643.x.
- ^ National Heart Lung and Blood Institute. Guidelines for the diagnosis and management of asthma. National Institute of Health; 2007
- ^ Cecil Adams (April 7, 2000). "Does a mattress double its weight due to dust mites and their debris?". The Straight Dope. http://www.straightdope.com/columns/read/2545/does-a-mattress-double-its-weight-due-to-dust-mites-and-their-debris. Retrieved September 19, 2008.
- ^ T. J. Kemp, R. W. Siebers, D. Fishwick, G. B. O'Grady, P. Fitzharris, & J. Crane (October 12 1996). "House dust mite allergen in pillows". British Medical Journal 313 (7062): 916–919. PMC 2352227. PMID 8876094. http://www.bmj.com/cgi/content/full/313/7062/916. "For many years asthmatic patients have been told to avoid using feather filled pillows on their beds, although there is no evidence to support this practice. Strachan and Carey's case-control study is the first to have directly challenged this assumption.1 This study showed that, after exclusion of asthmatic subjects whose bedding had been changed because of their disease, pillows with synthetic fillings were a risk factor for severe asthma. In the light of this finding, we have compared pillows with synthetic and feather fillings for their content of Der p I, the major allergen of the house dust mite Dermatophagoides pteronyssinus."
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- ^ "Hotter is better for removing allergens in laundry". American Thoracic Society. May 20, 2007. http://www.eurekalert.org/pub_releases/2007-05/ats-hib051407.php.
- ^ J. D. Miller, A. Miller (1996). "Ten minutes in a clothes dryer kills all mites in blankets". Journal of Allergy and Clinical Immunology 97 (1, part 3): 423. doi:10.1016/S0091-6749(96)81180-8.
- House Dust Mite site with research, animations and advice for patients and parents.
- Dust Mite Information – Allergies, biology, control measures and locating dust mites
- House dust mites on the University of Florida / Institute of Food and Agricultural Sciences Featured Creatures website
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