|University of Kentucky Entomology|
HOUSE DUST MITES
by Michael F. Potter, Extension Entomologist
University of Kentucky College of Agriculture
Introduction and Medical Importance
There are many substances in household dust which can cause allergies in humans, including animal dander, insect parts (especially from cockroaches), mold spores and pollen. The most common allergenic components of house dust, however, are from house dust mites. House dust mites are tiny creatures related to ticks, chiggers, and spiders, that live in close association with humans. Their primary food is dander (skin scales) shed from human and pet activity. Most homes in the United States probably have detectable levels of house dust mites and their allergy-producing fragments.
House dust mites are not parasitic nor are they capable of biting or stinging humans. Their significance as pests is due to the powerful allergens contained in the mites, their cast skins, fecal material and secretions. Symptoms of a house dust mite allergy include stuffy or runny nose, sneezing, coughing or watery eyes. Inhalation of dust mite allergens by hypersensitive individuals can result in acute attacks of bronchial asthma, accompanied by wheezing, shortness of breath, and perhaps even death. Diagnostic tests and clinical studies by allergists have shown house dust mite to be the most common allergy in asthmatics, and an important "root cause" for the development of asthma in young children. Recent studies suggest that at least 45 percent of young people with asthma are allergic to house dust mites. Unlike "seasonal" allergies caused by molds and pollen, people who are allergic to dust mites often will have symptoms year round. Mite Description and Detection
House dust mites are tiny adults are about 0.5 mm long and the immatures are even smaller. Consequently, they generally are visible only with the aid of a microscope. The mites are globular in shape, clear to creamy white in color, with hairs on their legs and body. There are two common species in the United States, the North American house dust mite, Dermatophagoides farinae, and the European house dust mite, D. pteronyssinus.
The presence of house dust mites can be confirmed by collecting dust samples from inside the home and examining them under a microscope. Another diagnostic test more accessible to householders can be purchased from drug and allergy supply stores. The detection kits (e.g., Acarex) measure the presence and infestation level by combining dust samples, collected from various places inside the home, with indicator reagents. Sensitivity to house dust mites and their allergenic proteins can be confirmed by an allergist-immunologist, via a skin and/or blood test.
Biology and Habits
House dust mites have specific environmental requirements for their development. The mites tend to be most numerous in warm homes with high humidity. Optimum conditions for growth and development are around 75-80 degrees F and 70-80 percent relative humidity. House dust mites absorb and lose moisture through their skin, and are very vulnerable to dehydration. Consequently, humidity levels within the home have a significant effect on survival. Dust mites cannot survive well at relative humidities below 50 percent. Although mite populations tend to be low in dry climates, most homes throughout the United States are capable of supporting dust mites. House dust mites and their allergenic particles are present within homes year round, but people tend to have fewer symptoms during the summer, perhaps because they spend more time outdoors.
Food is seldom a problem for house dust mites. Their primary food is skin scales (dander) contained in house dust. People and pets regularly shed small flakes of skin from their bodies as the skin continually renews itself. Since the greatest fallout occurs in areas of human and pet activity, the mites tend to be most numerous in beds, overstuffed sofas and chairs, and adjacent carpeted areas. Relative humidity also tends to be higher in these areas, because people perspire and exhale water vapor where they sleep and lounge. Mattresses, sofas, carpet, and other soft furnishings trap and accumulate dust, dander, and moisture, making them ideal microhabitats for mite development.
House dust mites go through five major life stages: egg, larva, protonymph, tritonymph and adult. Between life stages the mites molt, shedding their outer skin. When temperature and humidity are optimum, development from egg to adult takes about one month. Adults live approximately 1-2 months, and the females lay about 50 eggs. It is not uncommon to find thousands of mites in a single gram of house dust (a gram is about the weight of a paperclip). An infested mattress can contain millions of dust mites.
The allergenic proteins responsible for causing symptoms are contained within the mites themselves (alive or dead), their shed skins, and especially in their feces. Routine human activity such as housecleaning, walking or playing on carpeting, or making the bed, causes the tiny fecal particles to become airborne and inhaled.
Managing Infestations and Alleviating SymptomsThere are two basic approaches to managing dust mite allergy: 1) treatment of the patient, and 2) modification of the patients' environment to minimize exposure to the mites. An allergist may prescribe quick-relief medications and/or allergy vaccinations (immunotherapy). Immunotherapy involves injecting gradually-increasing concentrations of mite extracts over time in order to desensitize the affected individual.
The second approach often done in conjunction with patient therapy is to minimize exposure to the mites and their allergenic materials inside the home. This is not a simple process and usually requires significant effort and expense. Dust mite abatement has become a huge industry, with companies offering many products and services to allergy sufferers seeking relief from their symptoms. While some abatement measures are helpful, others are relatively ineffective or as yet unproven. Of the treatment measures discussed below, numbers 1-3 are generally considered most essential and effective, whereas the others may provide some secondary benefit.
Issued: 01/00 Revised: 01/00
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