Least toxic control for house dust mite

With dust mite products often including chemicals, this article looks at the actives registered for use in the UK and the non-chemical control options.

With over 3 million people in the UK suffering from asthma, and one in seven children affected(1), house dust mites along with pets are the most important source of allergens in the domestic environment. The most common mite in Europe, also found throughout the world, is the European house dust mite Dermatophagoides pternonyssinus which can trigger allergic reactions such as asthma, eczema and rhinitis. In sensitive individuals medical treatments can provide relief from these symptoms, but they are expensive and do not deal with the cure. This has led to research on both chemical and non-chemical methods of control for the house dust mite.

Biology
The life cycle from egg to adult of the house dust mite takes about one month in optimum conditions and passes through three immature stages (larva, protonymph and trito-nymph). They feed mostly on human skin scales (each person sheds approximately 1g of skin scales a day) but also on the scales of any small animals such as pets. Mattresses, carpets and other furniture fabrics act as dust traps and regulate environmental conditions suitable for mite population growth such as a higher relative humidity and temperatures of between 10°C and 32°C. There has been an increase in dust mite over the last few decades as more homes are carpeted, double glazed and central heated. They are so small (0.3mm long) that they cannot be seen by the naked eye and it is the faecal material from the mites and possibly their decomposing moulted skins that provide an allergic response.(2)

Chemical Control
Chemical control of the house dust mite comes in many forms, including aerosol sprays, gels, powders, liquids and foggers. The active ingredients registered for use against mites in domestic premises are listed in table1. Recently products have actually been impregnated with an active ingredient to kill mites. This is worrying in the case of individuals who are chemically sensitive as the combined effect of many different exposures may make people ill. Margaret Reichlin a sufferer with multiple chemical sensitivity who has extensively researched the issue states: "It is impossible to create a 'safe haven' in present circumstances with almost everything for the home now treated with something."
    An example of this is Courtaulds, the manufacturer, who impregnate their bedding with a fungicide called tolnaftate which is worked into the centre of the fibre and released slowly. MfZ Z-nets (Mite Free Zone), manufactured by Protec Health Ltd are covers for mattresses, duvets and pillows, designed to kill mites, fleas, bedbugs and lice. They are made from a low-dosage, permethrin impregnated fibre that provides a slow release into bedding. They are not recommended for children under two and should not be used in conjunction with other pesticides. Dynomite carpets are treated with isothiozolinone, a biocide derived from the synthetic pyrethroid permethrin to protect against dust mite. It works by preventing the formation of mould which acts as the predigester for the mites food. Isothiozolinone which is used widely in cosmetics is included in a list of common allergens and has led to cases of contact dermatitis. Individuals have been known to react to as little as 0.005%(3).
    It is difficult to obtain information on tolnaftate and isothio-zolinone as they are used in the manufacturing process of a product and not as a pesticidal treatment product covered by the Control of Pesticides Regulations, 1986. The labelling of chemical substances and preparations in the UK is regulated by the Chemicals (Hazard Information and packaging for Supply) Regulations 1994, (CHIPS). However, consumer items such as textiles and clothes are not covered by CHIPS.

Natural control
By reducing dampness in the home, the number of house dust mites can be diminished along with other unwanted pests and moulds. Ventilate rooms where cooking, washing or bathing takes place and close doors to other rooms. Air bedding before use and prevent build up of dust by regular cleaning, vacuuming all surfaces including blinds, curtains and upholstery. Mattresses should be vacuumed every two weeks (high efficiency filter vacuum cleaners are best). Exposing fabrics to high temperature washing (60°C) and placing soft toys into the freezer for 6 hours will kill house dust mites. Mites are found in large numbers in mattresses and pillows and they should be covered with micro-porous membrane covers. Use vinyl flooring or sealed natural flooring such as cork tiles instead of carpet, or cotton rugs that can be washed at high temperatures. If carpets are preferred then short pile synthetic types hold fewer mites than long piled wool carpets(6).

Comment
Chemical treatments for dust mites tend to be advertised as the solution to the problems of allergy sufferers although this is the very group of people who are more susceptible to allergic reactions to chemicals. The treatment is usually applied to carpets, upholstery and bedding, the areas where children spend most of their time. The Pesticides Trust [now PAN UK] believes this leads to undesirable exposure to pesticides over a long period of time and is unnecessary when non-chemical alternatives exist.

References
1. National Asthma Campaign, 23/11/98.
2. Common Sense Pest Control: Least-toxic solutions for your home, garden, pets and community. Olkowski, W., Daar, S. and Olkowski, H., Taunton Press, 1991, 159-164.
3. Isothiozolinone fact sheet, Royal Society of Chemistry, April 1997.
4. UK Health and Safety Executive list of pesticides used to control mites in domestic premises, 20/11/98.
5. Pesticides Trust [now PAN UK] Active Ingredient Database, 1998.
6. Leaflet on House-dust mites and asthma, Department of Environment, UK, 1995.

[This article first appeared in Pesticides News No.42, December 1998, p19]