Anti-allergy sprays Antimicrobial treatments Dehumidifiers

Public Health Significance of Urban Pests 113 Typically, cheyletid mites found in house dust such as Cheyletus malaccensis constitute only a small percentage of the total number of mites, and they are present mainly in car- pets, rather than mattresses Rao et al., 1975. In comparison with HDMs, their numbers are also lower than would be expected in a predator–prey population in equilibrium Colloff, 1991b; therefore, they are not suitable contenders for biological control. Also, previous studies have suggested that in the absence of suitable prey, Cheyletusmites may not only bite people in self-defence, but they may also feed on their body fluids Yoshikawa, 1980; Htut, 1994.

3.3.8.2. Air filters

The use of air filtration devices that incorporate high efficiency particulate air HEPA filters have the ability to filter or remove airborne allergens from the atmosphere, thus reducing allergen exposure to individuals in the room. These filters have been found to be of clinical benefit in a number of trials Zwemer Karibo, 1973; Villaveces, Rosengren Evans, 1997. However, most HDM allergens do not remain airborne unless disturbed Custis et al., 2003. Custis and colleagues 2003 found that an ion-charging device was able to remove HDM allergens from the air after disturbance, although their experiments were not designed to test the ability of this device to clean air. Colloff and colleagues 1992 concluded that HEPA filters were more effective than electrostatic filters and that air filtration should not be conducted in isolation from other forms of control.

3.3.8.3. Anti-allergy sprays

No published data are available on these treatments, which generally work by binding the allergen to the fibres of the article. Some products claim efficacy levels of up to 75 in reducing airborne allergens from a treated article. The effectiveness of these products may well be short lived.

3.3.8.4. Antimicrobial treatments

Recently, there has been a revived interest in the use of fungicides to control HDMs. This can be at least partially attributed to the reluctance of the general public to use insectici- des or acaricides within their homes. Antimicrobial treatments are primarily thought to retard HDM growth, by preventing fungal development on skin scales, thus reducing the nutritional value of the food available to HDMs see subsection 3.1.1.3. Studies using the fungicide Natamycin have reported mixed results Bronswijk et al., 1987. However, de Saint Georges-Gridelet 1988 found the treatment to be at least somewhat effective, which may have been caused by higher application rates. Some products can be applied topically or applied to carpets and soft furnishings prior to their sale. Fibres used in bed- ding materials can also incorporate an antimicrobial agent onto or into their structure. Little is published in scientific journals on the effectiveness of these treatments, although laboratory experiments conducted by private research laboratories have shown them to be effective in reducing the rate of HDM population growth. It should be noted that not all antifungal products have the ability to control HDMs.

3.3.8.5. Dehumidifiers

Custovic and colleagues 1995 investigated the use of portable dehumidifiers in the control of HDMs and mite allergens. They found that a single portable dehumidifier pla- House dust mites 112 materials that have been impregnated with acaricides. Therefore, studies that simply place mites onto fabrics impregnated with insecticides or that apply insecticides directly to mites should only be considered as being the first step in determining their potential in the field. An effective acaricide will only remove the source of the allergen, the HDMs; it will not remove or denature any allergen present. Colloff and colleagues 1992 advise that acari- cide use must be followed by an intensive and thorough vacuuming of the treated surfa- ces to remove allergens. De Boer, van de Hoeven Stapel 1995 found that samples of carpet treated with lindane showed only a very small decrease in Der p 1 levels over 18 months, although Der p 2 decreased by a slightly larger amount. The use of tannic acid, in combination with an acaricide, has been found to reduce allergen levels more effecti- vely than the use of acaricides alone Green et al., 1989. Alternatively, steam cleaning could be conducted just prior to the application of an acaricide. Also, Cameron 1997 reported that benzyl benzoate reduced mite allergen levels in carpet dust more than in mattress dust, which is likely due to carpets being cleaned more frequently than mat- tresses. In Europe and elsewhere, there is a shift away from the use of insecticides, particularly in the domestic environment. Colloff 1986 discussed the risk of using acaricides or insec- ticides in the presence of atopic individuals, because of possible sensitization, although he did state that no occurrence of toxicity was reported in people due to these treatments. More recently, in agreement with the United States Environmental Protection Agency EPA 2000, a company removed a benzyl benzoate based acaricidal product from the market, as a small percentage of consumers reacted adversely to a fragrance used in its formulation. Problems reported included asthma attacks, respiratory problems, burning sensations and skin irritation. This case highlights the care needed in formulating pro- ducts for use by people with allergies. Many of the other control methods described in this chapter can be used instead of acaricides. If acaricides are used, it is essential that they be applied correctly and in such a way as to minimize any direct contact with people during and after treatment.

3.3.8. Other methods