Sydney University Department of Medical Entomology Westmead Hospital
Dust Mites

Dust mite

modified from: Kettle, D.S. (1995). Medical and Veterinary Entomology. CAB International. Wallingford

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Natural History

The most common species of dust mite isolated in Australia is Dermatophagoides pteronyssinus from the family Pyroglyphidae, but there are other species of dust mite as well as predatory mites that share the same dusty environment. Dust mites live in the fine layer of minute dust particles that continually settles on household items. They are found almost world wide but their numbers are considerably reduced at high altitudes and dry climates. House dust mites have been known to be associated with allergies since the 1960's and have become a focus over the years for their involvement with respiratory ailments. They do not bite or sting but harbour strong allergens in their bodies as well as in their secretions, excreta and shed skins. Constant contact with these allergens can trigger respiratory and dermatological complaints in some humans. Dust mites favour homes with high humidity levels and constant warm temperatures, and under these conditions mite populations explode, although there are some seasonal fluctuations. The mites are known to concentrate in high traffic areas in homes and on certain furniture items, especially beds, upholstered lounges, chairs, and in carpets with long fibres. They are attracted to these areas for food, and they feed on shed human skin scales and secretions, house dust, fungal spores, pollen grains, plant fibres, and insect scales. Dust mites dislike strong light and will take harbourage in the seams, ledges, and framework of furniture when exposed. Due to their light weight, dust mites can become airborne during activities such as bed making, and in this way can be distributed throughout the room or house.

Adult mites are described as white to a light tan in colour; they are difficult to see with the naked eye, as they measure only 0.5mm in length, and the developmental stages are smaller. The body of the mite is oval shaped and covered with fine striations. There are five stages in the life cycle of a dust mite; from the egg, the larvae stage, then two nymphal stages, and finally the adult. The whole life cycle from egg to adult takes approximately one month to complete, mature female mites can lay from 1-2 eggs per day. Adult mites can live up to two months but this is dependent on the levels of humidity and temperature of their surrounding environment.

Clinical Presentation

There is not one single clinical symptom that can readily identify mite-allergic asthmatic patients. This makes a clinical diagnosis difficult, and is therefore dependent on the reporting of other associated features. There is a proliferation of allergy clinics that specialise in testing for allergic responses to different materials including dust mites using skin prick tests. Medical conditions that are attributable to the presence of dust mites include allergic rhinitis, asthma, childhood eczema and other allergic conditions. Dust mites do not transmit any disease-causing pathogens.

Laboratory Diagnosis

Identification of dust mites is performed with the use of light microscopy and taxonomic keys, after the specimen has been extracted by flotation and/or sieving methods from the dust substrate and especially prepared on a glass slide.

Treatment and Control

Allergies from house dust mite can be managed by immunotherapy using mite extracts in conjunction with reducing the mite population in the home of the patient. It is virtually impossible to eliminate all dust mites from a household, but areas where mites tend to congregate can be targeted. Wall to wall carpet should be reduced, and replaced where possible with smooth hard surfaces that are easy to clean. Upholstered furniture can be avoided, mattresses and pillows should be encased in especially manufactured (‘plastic’) products that aid in the exclusion of mites. Bedding and curtains should be selected on their ability to withstand frequent laundering. Thorough vacuuming on a regular basis, including all mattresses, especially the seams and framework of the bed, will also help. A reduction in humidity levels by increased air circulation and ventilation throughout the house will assist in maintaining mites at a lower level.

Confirmation & Enquiries

Information and identification of mites, and all other medically important arthropods, is provided through the Medical Entomology Department at ICPMR, Westmead Hospital.

See 'Contacts' for further information.

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