The House Dust Mite

Jul 26, 2009 Features / Columnists, Interesting Creatures in Guyana

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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. Some of the gut enzymes (notably proteases) produced by the house mite persist in their faecal matter, and can be strongly allergenic. 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 420 micrometres in length and 250 to 320 micrometres 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). Dust mites can be transported in dust bunnies or airborne by minor air currents generated from normal household activities.

The average life cycle for a male house dust mite is 10 to 19 days. A mated female house dust mite can live for 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 2000 faecal particles and an even larger number of partially digested enzyme-covered dust particles. A simple washing will remove most of the waste matter.
Both being exposed to temperatures of over 60 degrees Celsius (140 degrees Fahrenheit) for a period of one hour, freezing, or exposure to temperatures below 20 °C (68 °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 enough to kill all the dust mites in bedding. House dust mites reproduce quickly enough that their effect on human health can be significant.

The house dust mite survives in all climates, even at high altitude. A person sheds about 1.5 grams of skin cells and flakes every day (approximately 0.3–0.45 kg per year), which is enough to feed roughly a million house dust mites under ideal conditions. If trying to control house dust mites, humidity should be kept low. House dust mites thrive in the indoor environment provided by homes, specifically in bedrooms and kitchens. They survive well in mattresses, carpets, furniture and bedding. Even in dry climates, house dust mites survive and reproduce easily in bedding, especially in pillows, deriving moisture from the humidity generated by human breathing, perspiration, and saliva.
House dust mites consume minute particles of organic matter. These creatures 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. House dust mites eat the same particle several times, only partially digesting it each time; between feedings, house dust mites leave particles to decompose further. Only when the particles are fully digested do they enter the dust mite’s faecal matter.

Allergens produced by house dust mites are among the most common triggers of asthma. Some main signs of house dust mite allergies are itchiness, sneezing, inflamed or infected eczema, watering/reddening eyes, runny nose and clogging in the lungs.
Avoidance of dust mites and their allergens is the best course of action for those with dust mite allergies. The use of bedding that acts as a barrier to the dust mite and its allergens is a good first step, the bedding should also be breathable and be able to withstand frequent washing. However a home allergen reduction plan has been recognised as being an essential part to the management of asthma symptoms and therefore all aspects of the home environment should be considered such as proper vacuuming, use of air cleaners, off-gassing from paint and cleaning products.

Most people who have dust mite allergy sneeze when they wake up in the morning. They will generally feel better as they go out of their rooms, then at night when they sleep, the cycle repeats over again. This can cause the allergy to be chronic and long lasting.
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 faecal 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. The reverse, however, is true. It has been established that Boron powder is often used to eradicate house dust mites.
(Source: Wikipedia – The Free Online Encyclopedia)

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