GB2280851A - Method of pest control using steam - Google Patents

Abstract

A method of pest control which incorporates an improved anti-allergy treatment to reduce the number of asthma attacks and other allergic reactions in people who are sensitive to house dust mites, comprises the use of steam, preferably pressurised at 80 DEG C or above, to destroy the pests. House dust mites live in vast numbers in carpets, mattresses and upholstery in domestic dwellings and these articles can be steam treated to eradicate a pest which is responsible for attacks of asthma in over 80% of Britain's three million asthmatics and other allergy sufferers. The present invention obviates the disadvantages inherent in prior anti-allergy treatment by using water, heated in a portable steam generator 1 to produce pressurised steam 2 delivered through a flexible 3 and rigid 4 hose via a nozzle with holes or jets 5 to deliver the steam to the area being treated 6 to effectively destroy house dust mites 7 and simultaneously neutralise the harmful effects of the allergy triggers they produce 8.

Description

IMPROVED METHOD OF PEST CONTROL The present invention concerns a method of pest control. It concerns also an improved antiallergy treatment, especially but not exclusively a treatment to reduce the allergic effects on humans by the house dust mite Dennatophagoidespteronysstnus.

Pests in the form of house dust mites, fleas, silver-fish, cockroaches, ants or carpet beetles can infest carpets, mattresses, upholstered furniture and other areas of the home and a first object of the present invention is to produce a reliable method of eradicating them.

A substantial and increasing proportion of the population suffers from asthma and many asthma attacks are caused by house dust mites. It has been established that by controlling dust mite numbers, asthmatics show considerable improvement with a reduction in the frequency and severity of attacks.

House dust mites live in massive quantities wherever their main food supply, shed human skin scales, is plentiful. High relative humidity levels (between 55% and 75%) and temperatures of between 13 degrees Celsius and 25 degrees Celsius are also a requirement for large mite concentration. The principal infestation sites in domestic homes are mattresses, carpets and upholstered furniture.

House dust mites produce a protein which is concentrated within their droppings. If inhaled or ingested this protein or allergen has been shown to trigger allergic reactions in people suffering from asthma, eczema, rhinitis and other dust allergic conditions. Dust mite allergen can become airborne by normal domestic activity.

House dust mites are not insects and consequently are virtually insensitive to insecticides. Antimite products, containing active toxins, known as acaricides, are necessary to kill them.

It has been believed that reducing mite numbers alone would lead to a significant improvement in the allergic patient's condition. However several published trials have shown that this is not the case as, even following the eradication of a current generation of house dust mites, during the interval between eradication and subsequent re-infestation (believed to be three to six months) no significant decrease in mite allergen level was detected.

Furthermore, the use of anti-mite products containing active toxins used to kill house dust mites may have an adverse effect on the allergic patient as the long term effects of exposure to the active toxins used in the products are uncertain.

It is a second object of the present invention to obviate or mitigate the disadvantages inherent in prior anti-allergy treatment.

According to a first aspect of the present invention there is provided a pest control treatment comprising rapidly increasing the temperature of the article being treated to at least 80 degrees Celsius by the application to the article of pressurised steam to achieve the temperature increase.

According to a further aspect of the present invention there is provided an anti-allergy treatment comprising increasing the temperature of the article being treated to at least 80 degrees Celsius thereby denaturing and rendering harmless to the allergic patient the heat sensitive house dust mite allergens contained within the article being treated.

Preferably the steam is produced by means of a steam generating appliance.

Preferably the steam is dispensed via an insulated flexible and or rigid tube or hose, fitted with a nozzle or brush containing several holes or jets.

Preferably the application of pressurised steam increases the temperature of the article being treated to 100 degrees Celsius.

Preferably the treatment is repeated three or four times per annum.

The embodiment of the present invention will now be described by way of example only.

The treatment of the present invention is intended to reduce the effect of the house dust mite on allergy patients by carrying out a two-stage process, the first of which is to destroy the house dust mites contained in or on the article, which may be a carpet, mattress or item of upholstered furniture, and the second of which is to denature the house dust mites' faecal pellets produced prior to their eradication. The high temperature of the pressurised steam will also denature other heat-sensitive allergens.

Killing is achieved by increasing the temperature of the article being treated beyond a level at which life can be sustained by the dust mite. It is believed that a temperature of 60 degrees Celsius or higher is sufficient and the present invention achieves an increase in temperature to at least 80 degrees Celsius and preferably 100 degrees Celsius.

Temperature increase is achieved by treating the surface of the article with pressurised steam delivered via a flexible and or rigid insulated tube or hose fitted with a nozzle or brush containing holes or jets on the underside to permit the free passage of the pressurised steam.

The main constituent of the pressurised steam is tap water. It is colourless, odourless, non staining and is readily available. The process uses no solvents, detergents, or active toxins and produces no harmful waste products which may harm the environment.

Furthermore as the steam can be generated under pressure, which has the effect of reducing its overall water content, the treated article does not become excessively wet or damp.

The rate of cooling of the article back to ambient room temperature is entirely dependent upon ambient room temperature. Return to ambient room temperature is normally achieved within minutes.

In certain instances of the treatment calls only for the killing of the pests, for example house dust mites, fleas, ants, silver-fish, cockroaches, or carpet beetles, the second stage of the treatment is believed also to neutralise or denature the harmful effects of the allergen produced by these pests.

Various modifications can be made without departing from the scope of the invention, for example, an alternative steam generator which does not pressurise the steam could be employed; likewise a steam delivery system other than a flexible or rigid tube or hose connected to a nozzle or brush with holes or jets could be employed.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to whether or not particular emphasis has been placed thereon.

A controlled trial which has been carried out to prove the effectiveness and efficiency of the invention is now included.

The use of domestic steam treatment for the control of house dust mites Mj. COIÒFF*t, C. A. TAYLORt, T.G. MERREIl *Department of Immunology, University of Glasgow, UK, and Scottish Parasite Diagnostic Laboratory, Stobhill Hospital, Glasgow, UK, #Medivac plc, Bollin House, Wilmslow, Cheshire, UK, AIIergy Analysis Centre, Glyn Rhonwy, Llanberis, Caernarfon, Gwynedd, UK Summary A steam generating appliance was used to treat carpet squares which had been seeded in the laboratory with known numbers of house dust mites, Demzatophagoides pteronyssinus. The number of live mites was monitored for a period of 4 months in 8 treated carpet squares and 8 controls. No live mites were found at any time in the treated squares, whereas in the control squares geometric mean mite population density rose from 11 after 3 days to 39 after 1 month, 66 after 2, 122 after 3 and 185 after 4 months.

Dust samples were taken from 12 standardised areas of carpet in a tenement flat in Glasgow, UK, before and after steam treatment, and the concentration of allergen Derp 1 was compared with 12 adjacent, control areas. There was a statistically significant mean reduction of 86.7% in Derp 1 concentration (3.3-0.44 g/g; P < 0.01) compared with a reduction of 4.7% (2.22-2.116 I.Lglg; P not significant) in control areas. These data indicate that steam treatment has considerable potential as an highly effective and efficient method of killing house dust mites and reducing concentrations of Derpl in domestic premises.

Introduction There are a large number of methods available for the control of house dust mites, both chemical and physical [reviewed in 1]. One category involves the exploitation of extremes of temperature and humidity. These methods include freezing, both with liquid nitrogen [2,3] and using domestic 'fridge/freezers for small items such as pillows and childrens' soft toys; dry heating with electric blankets [4,5], hot-cycle washing in domestic washing machines [6,7], drying with silica gel [8], dehumidifiers [9], mechanical ventilation systems [9-12] or by passively airing rooms and bedding [13,14]. Although steam treatment of bedding and other fabrics is performed commercially and in hospital laundries, there has been no attempt until now to examine the feasibility and efficacy of steam treatment for the eradication of house dust mites in a format that could be used within domestic premises.

We investigated if a steam generating appliance was effective at killing house dust mites and their eggs in vitro, what temperatures were required, and whether the steam had any effect on concentrations of a major dust mite allergen, Derp 1, in vivo.

Materials and Methods Laboratory investigations: carpet squares (Kosset High Esteems; Coloroll Carpets Ltd, UK) made of 100% nylon (StainmasterB; Dupont Ltd, UK), of dimensions 45 x 45 cm (2025 cm2) and pile depth 1.5 cm were seeded with house dust mites as follows: cultures of Dennatophagoides pteronyssinus were reared in the laboratory in a culture medium consisting of a 1:1:1 mix of bakers' yeast granules, wheatgerm and dried Daphnia at 27 degrees Celsius, 85% RH. Cultures were pooled, sieved through a nest of test sieves (Endecott Ltd., UK) of mesh size 1000-37 ttm, and the fraction of size range > 75, < 300 jim, which consisted almost entirely of live mites, was weighed into 3 aliquots of 100 mg each. The mites were killed by immersion in liquid nitrogen and counted under a stereobinocular microscope to determine numbers of mites per unit weight.

A total of 16 carpet squares were frozen overnight at -30 degrees Celsius, thawed, and vacuum cleaned thoroughly. The vacuum samples were examined for live mites (cf. below). Having assessed that the carpet squares contained no live mites, each square was seeded with 500 mg live mites, equivalent to an arithmetic mean of 9209 mites/square (range 8610-9745; or 4.34.8 mites/cm2), and 3 g of fresh, mite-free culture medium. The mites and culture medium were distributed evenly over the surface of the carpet squares and gently brushed in. The squares were then incubated at 23 degrees Celsius, 75% RH for 72 hours to allow the mites to settle and disperse within the carpet.

After this period, 8 carpet squares were kept as untreated controls and 8 squares were steam treated. Steam was delivered from the boiler via a hose outlet with a brush attachment covered in a treatment rag. The boiler was operated at full power and pressure (2,000W, ca. 320 kPa) according to the designer's instructions. Temperature and humidity were monitored at the base of the carpet pile before, during and after steam treatment using an electronic thermohygrometer, coupled through a digital analogue converter to a pen recorder [15].

Following treatment, each square was left to cool. and dry (c. 30 min - 1 hr). The treated and control squares were then vacuum-sampled for 30 sec per square using a Medivac medical dust sampler (flow rate 2.2 m3/min; Medivac plc, Wilmslow, UK) fitted with a 25 jim nylon mesh filter contained within a cylindrical sampling tube which was attached to the sampler hose.

Sampling was repeated at 28-day intervals on 4 occasions.

To count the numbers of live mites, the material adhering to the filter was recovered and weighed and the mites extracted according to the method of Arlian et al [16]. In brief, the whole sample was suspended in 50 ml saturated sodium chloride, wetted with 1-2 drops of domestic washing-up liquid, stirred, filtered through a 37,am mesh test sieve (Endecott Ltd., Uric), rinsed with tap water and stained on the sieve using 1% aqueous crystal violet. Excess stain was rinsed out and the mites and culture medium transferred to a 9 cm diameter glass Petri dish. Active, live mites were then counted under a stereobinocular microscope at x 20 magnification.

Following the final vacuum sampling, each of the treated carpet squares was further assessed for the presence of live mites using the heat escape method of Bischoff and co-workers [17].

The underside of the carpet squares were heated on a hot plate at 80 degrees Celsius for 15-30 min. The live mites, if present, move away from the heat source and become stuck to strips of transparent adhesive tape laid over the top surface of the carpet square. We used 3 x 100 cm2 strips of tape per square, which were removed after heating and examined under a stereobinocular microscope for the presence of live mites.

Field investigations: two adjacent areas, each of 0.25 m2, were delineated with a quadrant and masking tape on bedroom, living room, kitchen and hall carpets in a ground-floor tenement flat in Glasgow, UK The flat was ca. 100 years old, of sandstone block construction, with no signs of damp or mould growth. The proprietors were non-atopics, and the carpets were 10-15 years old. Dust samples were taken from each area, as described in the laboratory investigations section above. One area was then steam treated and the other left untreated. After allowing the treated carpet to dry, another dust sample was taken from each area.

Dust samples were weighed and diluted to 1:20 (w/v) in PBS, vortexed, mixed by rotation for 2 hours, centrifuged at 1000g for 15 min.; the supernatant was removed, sterile filtered and stored at -30 degrees Celsius until use. Derp 1 was assayed using a two-site monoclonal antibody ELISA, as described previously [18].

Statistics: before- treatment and after-treatment values of Derp 1 were log. (n+l) transformed and analysed using two-tailed, paired t-tests. Derived means were calculated from the arithmetic mean of log. (n+l) transformed values using antilog.

(x transformed values) - 1. The 95% confidence limits (c.l) were likewise calculated using transformed values which were then converted back into the original scale.

Results Laboratory investigations: no live mites were found in any of the vacuum samples, nor the heat escape samples, taken from the 8 steam-treated carpet squares. By way of contrast, the numbers of live mites in the 8 control squares rose from a geometric mean of 11 on day 3 post-seeding, to 39 after 1 month, 66 after 2,122 after 3 and 185 after 4 months (Fig. 1).

Temperature and relative humidity of carpet squares were at ambient prior to treatment (24.7 degrees Celsius, 49.6% RH). The temperature in the 8 carpet squares during treatment rose to an arithmetic mean maximum of 103.4 degrees Celsius (range 97.9-121.3 degrees Celsius) and declined to ambient within 20 min. Humidity increased to saturation within 10 sec. of applying steam, remained at saturation for 25 min and fell to ambient after 140 min.

Field investigations: there was a derived-mean reduction in Derp 1 concentration from 3.3 (95% c.l. range: 1.14-7.64) to 0.44,ug/g (95% c.l. range: 0.19-0.74) in areas of carpet that were treated with steam. This represents a derived-mean reduction in Derp 1 concentration of 86.7%. By way of contrast, there was a derived mean reduction from 2.22(95% c.l. range: 0.645.35) to 2.12 ,ig/g (95% c.l. range: 0.634.94), equivalent to 4.7% and not statistically significant, in the adjacent, control areas that were not steam treated but were sampled before and after the areas were steam treated (Fig. 2).

Discussion The fact that no live mites were found in any of the 8 steam-treated carpet squares at any time during the laboratory study indicates that steam-treatment is a highly efficient method of killing house dust mites in carpets. In order to check that the absence of live mites was not an artefact of the low efficiency of vacuum sampling as a means of recovering live mites [17], we used the heat escape method on the carpet squares after we had finished the vacuum sampling regime. It has a far higher extraction efficiency than vacuuming, in the order of 30-60% recovery [17], but again, no live mites were found.

The results of the field study demonstrate clearly the considerable reduction in Derp 1 concentrations achieved by steam-treatment. However, this study does not demonstrate, nor does it seek to demonstrate, an unequivocal effect of heat on the chemical denaturation of Der p 1. This has been shown by Lombardero et al. [19] who found heating Derp 1 at 100 degrees Celsius for 10 min. reduced the binding of ire antibodies by > 100-fold in competitive inhibition radioimmunoassays. But they also found that the major allergen Derp 1 was heatstable. This was confirmed by Stewart et al [20], who also investigated the effects of heat on three serine proteases of Dermatophagoides spp.: trypsin (Group III allergen); chymotrypsin (Group V1) and an allergenic elastase-like enzyme. They found that all protease activity was lost after treating spent mite growth medium at 65 degrees Celsius for 200 sec., although it is not clear whether there was a concomitant effect on allergenicity. Nevertheless, these data serve to indicate the possibility that the IgE binding activity of major dust mite allergens other than Derp 1 may be adversely affected by heat.

In the present study it was not possible to discriminate between whether allergen was being denatured or selectively retained in the carpet in some way as a result of the steam-treatment process. However, a comparison of the weights of dust samples removed from treated areas before and after treatment indicated there was no significant difference compared with the control areas (data not shown). This strengthens our contention that the reduction inDerp 1 concentrations was due to the denaturing effects of heat and not to retention of allergen in the carpet.

Steam is the product of water heated under pressure. It is capable of reaching temperatures well in excess of the boiling point of water at atmospheric pressure. The maximum temperatures achieved in the 8 carpet squares during steam-treatment in the laboratory study exceeded 100 degrees Celsius in all but two cases, reaching an absolute maximum of nearly 122 degrees Celsius. Following treatment, temperatures in excess of 90 degrees Celsius were maintained at the base of the carpet pile for up to 3 min. These temperatures and durations are likely to achieve a similar degree of denaturation ofDerp 1 to that recorded by Lombardero et al [19].

Steam treatment requires nothing more than water and heat and, therefore, is nonpolluting compared with mite eradication methods that require the use of detergents and other chemical agents. Furthermore, the design of the steam appliance renders it safe for domestic use as long as the manufacturer's instructions are followed; the risk of scalds could be considered no greater than that from an electric kettle. We observed no damage or shrinkage of the fabric of any of the treated carpet squares, nor discolouration, and the carpet dried out within half an hour of treatment. There is no indication of prolonged retention of residual moisture, as may be the case with wet vacuum treatment and which may promote population growth of mites that colonize subsequent to treatment.

Finally, steam-treatment as reported herein is the only method of house dust mite control that combines effective killing of mites and substantial reduction in allergen concentrations within a single system. These factors, taken together, render domestic steam treatment apparatus especially suitable for the management of house dust mites and their allergens in the homes of people with asthma and mite-mediated allergies.

Acknowledgements We wish to thank Dr RWA Girdwood and Professor Huw Smith (Scottish Parasite Diagnostic Laboratory, Department of Bacteriology, Stobhill Hospital, Glasgow) for provision of facilities and their encouragement and advice during the course of this study.

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Legend to fig.1 Total numbers of live mites extracted from 8 steam-treated carpet squares () and 8 untreated control squares () ) at 3 days after seeding the squares with live mites, then monthly intervals for 4 months; with geometric mean of tortal mites in untreated carpet squares (... ...).

Claims (11)

1. CLAIMS 1. Improved method of pest control, means using steam to destroy pests and to denature allergen contained within the article being treated.
2. 2. Improved method according to Claim 1 wherein pests means house dust mites, fleas, bed bugs, cockroaches, ants, carpet beetles or silver-fish.
3. 3. Improved method according to Claim 1 wherein the allergen is produced by house dust mites, fleas, bed bugs, cockroaches, carpet beetles, ants, silver-fish, plants, rodents or domestic pets.
4. 4. Improved method according to Claim 1 wherein the articles being treated means carpets, rugs, mattresses, bedding, upholstery, furniture, curtains, floor, ceiling, wall, or window coverings, furnishings, soft toys, or articles of clothing.
5. 5. Improved method in Claim 1 means steam produced by a steam generator.
6. 6. Improved method in Claim 5 means that the generator is portable.
7. 7. Improved method of pest control, in Claim 1 means the steam may be either pressurised or non pressurised.
8. 8. Improved method of pest control, in Claim 1 means steam delivered to the article being treated is via a flexible or rigid tube or hose.
9. 9. Improved method in Claim 8 means a flexible or rigid tube or hose may be insulated to prevent burns.
10. 10. Improved method in Claim 8 means having a nozzle or brush connected which contains holes or jets.
11. 11. Improved method in Claim 10 means to permit the free passage of steam into or onto the article being treated.