The Housedust mite (Dermatophagoides pteronyssinus) is a harmless minute 8-legged spider-like creature impossible to see with naked eye which lives in warm home environments such as human bedding, carpeting and furniture fabric.
It is about 1/3 of a millimeter in length and feeds on the dead skin scales of humans that have been modified by a fungus, it thrives in warm humid temperatures and is much more common an coastal homes.These people can be identified by means of skin prick tests (SPT) or RAST tests done on a blood sample. In fact there are roughly 10 000 housedust mites in the average bed!
The female mite lays about 50 eggs in her 6 week lifespan. The main cause of allergic symptoms in humans is the protein Der. p.1 found in the excretion pellets of the mite, of which about 20 pellets are excreted by each mite per day.
Certain people will develop an allergy to the tiny protein particles of Der.p.1, if they breathe them in the air and this may result in asthma and/or hayfever or on the skin exacerbate eczema. These people can be identified by means of a skin prick test (SPT) or RAST tests done on a blood sample.
The following measures are aimed at reducing the levels of the mite and its excretion products in the home and especially the bedroom where on average people spend a third of their lives.
|PILLOWS: Never use feather pillows, duvets or eiderdowns, but rather synthetic foam or polyester/acrylic filled bedding. Even foam pillows should be replaced every 6 months as mites may infest them. Both the pillow and mattress should be placed in the sunlight for 5 hours every week so as to kill the mites.|
|MATTRESS: Cover the mattress completely with a plastic, vinyl or microporous material such as shower curtaining and sew up or seal the ends. The mattress cover should also be washed regularly. If double bunk beds are used, make sure that the patient sleeps on the top bunk.|
|CARPETS: Replace fitted carpets with either vinyl or floor tiles. Wooden floors should be polished with wax regularly so as to seal them. If carpets must be used, rather have a low pile type or washable scatter rugs.|
|SOFT TOYS: All dust collecting soft toys, books, dried flowers, thick heavy curtains, venetian blinds, upholstered furniture and clutter should be removed from the room. Select closed bookcases and cabinets instead of dust collecting open shelves. Window shades and washable curtains are easier to keep dust free. The room should have a minimum amount of furniture, preferably made of wood or plastic. "Special" soft comforters may be washed every month, wrapped in a plastic bag and placed in the freezer overnight to kill any mites.|
|VACUUM: The room including the mattress should be vacuum cleaned daily if possible (otherwise a minimum of twice weekly), by someone other than the patient. If the patient has to vacuum the room, then a Dust Mask should be worn. The vacuum cleaner should have a leak free microfilter to trap mites and prevent them being recycled back into the room air. Unfortunately very few living housedust mites are sucked up because they have claws designed to keep them in place. Twice weekly damp dusting should be carried out on all surfaces.|
|VENTILATION: Make sure the room is well aired every day, and make use of air conditioners if available. No pets should be allowed to come into the room. All clothing and bed linen must be washed every 2 to 4 weeks at temperatures of 60 degrees or more.|
Electric blankets in winter will help eradicate mites from the bed. Humidifyers should be discouraged and ionisers have been shown to be of no benefit. Clothing should be kept in a cupboard and dust trapping clothes such as blazers should be dry cleaned whenever possible. No one in the home should smoke as cigarette smoking has been shown to promote allergic symptoms
in sensitive people. Any other rooms which are frequented regularly by the housedust mite allergic person (especially the living room ), should also have mite eradication measures applied to it.|
The Acarex test (a guanine assay) is a useful commercially available kit to measure housedust mite levels in the bedding, carpets and furniture fabric.
|ACAROSIDES: Certain chemical sprays such as benzyl benzoate (Acarosan), tannic acid, bromopol (Metsan) and liquid nitrogen will kill mites. These agents must be used regularly. Dead mites are more easily vacuumed up, so thorough post treatment vacuum cleaning is essential. Conventional insect sprays are of no benefit and may aggravate allergic symptoms.|