Dust Mites and Antimicrobials

  Dust Mites and Antimicrobials

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.

[private]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.

House dust mites are tiny adults and at maturity are about 0.5 mm long. Consequently, they are usually only visible with the aid of a microscope. The mites are 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.

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.₍₁₎  Sound creepy? You bet.

There is more to this story. Why is the humidity and temperature so important to the survival of dust mites? Dust mites have a primitive gut that needs the help of fungi to process their food. Because dust mites rely on fungus to process their nutrients, if the fungus isn’t there to help process the food for the dust mites – the dust mites starve and die off. Keeping the humidity in your home below 50% is one way to reduce fungi.₍₂₎ However, it isn’t always practical to keep the relative humidity in your home under 50% but there are other ways to control the fungus in your home without worrying obsessing about the humidity levels and, by doing so, control the dust mite problem in your home.

Antimicrobials keep both bacteria and fungi from growing. Stopping the growth of fungi in a home stops the skin cells from being processed into dust mite food. When that happens dust mites die off. The USEPA registers antimicrobials based on their use. In other words there are antimicrobials that are specifically approved for use by the EPA to control the growth of fungus on textiles products such as bedding, upholstery, carpeting and even clothes. The antimicrobials approved for use on bedding, upholstery, carpeting and clothes have provided extensive toxicological data to the USEPA to demonstrate there safety during such use. Some of these antimicrobials are based on natural substances and not only prevent dust mite growth but also improve the sustainability of the treated products.

The IAC provides step by step instructions to its members regarding how they can implement a dust mite control strategy for their products. To become a member of the IAC go to www.amcouncil.org/membership.

(1) ENTFACT-646, DUST MITES, by Michael F. Potter, Extension Entomologist,
University of Kentucky College of Agriculture

(2) Interactions between Domestic Mites and Fungi, Laurent Van Asselt,