Method for controlling dust mites

A method for reducing the proliferation of dust mites in substrates inhabited by dust mites is accomplished by contacting the substrates such as bedding materials, rugs and upholstered furniture with a sufficient amount of finely divided salt which functions as an acaricide against dust mites, thereby killing the dust mites.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method for reducing the population of dust 
mites by contacting salt crystals on substrates inhabited by dust mites. 
2. Background of the Invention 
It has been known for many years that common house dust is an important 
cause of asthma, rhinitis and eczema in allergic individuals. The mite 
Dermatophygoides pteronyssinus has been identified as a major source of 
house dust allergen. This mite and the related mites D. farinae, D. 
microceras and Euroglyphus maynei are the predominant house dust mites in 
temperate climates in countries including the United States and Europe. 
Dust Mites are not insects, but are eight-legged arachnids, relatives of 
ticks and spiders. They live in close association with humans (or other 
mammals), their main food source being the shed scales from skin. Adult 
mites are approximately 300 microns (3/10 mm) in size, having developed 
over approximately 25 days through egg, larval and nymph stages. Adults 
live for 2 to 31/2 months, during which time each female can produce about 
20-40 eggs. Dust mites are photophobic, living deep in pillows, 
mattresses, carpets, upholstered furniture and other soft materials. 
In addition to a food source, the other essential requirement for dust mite 
growth is adequate humidity. Dust mites are 75% water by weight. They do 
not drink water, but must absorb water vapor from the air in order to 
survive. Specialized glands above their first pair of legs produce 
secretions high in sodium and potassium chloride, which act to absorb 
water vapor from surrounding air. This can only be accomplished if the 
surrounding humidity is sufficiently high. Relative humidities of about 
70-75% are optimal for dust mite growth. Dust mites will die at humidities 
of 50% or less. In geographical areas where humidity is high, dust mites 
are present in nearly all homes and may be as plentiful as 18,000 mites 
per gram of dust. Literally millions of mites can inhibit a single bed or 
carpet. 
About ten years ago, it was demonstrated that a major dust mite allergen 
was present in mite fecal particles. Each mite produces about 20 fecal 
particles per day, and more than 100,000 of them may be present in a gram 
of dust. These fecal particles vary from about 10 to 40 microns in size, 
comparable to the size of pollen grains, and become airborne during 
domestic activity such as making beds and vacuuming carpets. The chemical 
structure of mite allergens has been defined, including that of other 
allergens which are present both on mite bodies and fecal particles. 
Acute exposure to mite allergens has been shown to provoke wheezing, 
rhinitis, eustacian tube obstruction or eczema in sensitized patients. 
Chronic exposure can cause bronchial hyper-reactivity and chronic asthma. 
There is a correlation between the level of exposure to house dust mite 
allergen in early childhood and the likelihood of the subsequent 
development of asthma. Conversely, asthmatics sensitive to dust mites 
improve in environments without mites, such as at high altitudes or in 
hospital rooms. Attempts have therefore been made to decrease patients' 
exposure to dust mites in the home. 
Studies of dust avoidance measures in homes have shown that the use of 
impermeable mattress and pillow encasings and the removal of bedroom 
carpeting are associated with a decrease in mite counts. These measures 
have also been shown to be of clinical value, with a decrease in symptoms 
and medication requirements occurring in children and adults with 
dust-sensitive asthma when pillows and mattresses are encased and carpets 
are removed. 
Although carpets and upholstered furniture are major sites of dust mite 
growth, many allergic individuals are unable or unwilling to remove these 
from their home. Vacuuming does not remove dust mites or significantly 
decrease dust mite allergen levels, and in fact, vacuuming of carpets 
actually increases the amount of airborne dust. It is thus not surprising 
that trials employing vacuuming rather than removal of carpets failed to 
produce clinical improvement. 
Because of the importance of carpets and textile materials as habitats of 
dust mites, various chemical acaricides have been proposed to kill mites 
in those locations. 
U.S. Pat. No. 4,666,940 to Bischoff et al discloses an acaricidal 
composition whose active ingredient is benzyl benzoate. The acaricidal 
substance is said to be applicable in the form of a liquid, a foam, or as 
a semi-aqueous pulverulent cleanser. The particle sizes of the residue 
after application and drying range from about 2 to 100 microns, which is 
said to be a suitable size range for oral ingestion by dust mites. 
Other chemical agents which have been used to kill dust mites include 
primiphos methyl, natamycin, bioallethrin, deltamethrin and methoprene. 
These organic compounds may be expensive, and many of them have caused 
skin, eye or bronchial irritation. They also have the potential to cause 
allergic or other adverse reactions. The use of such organic compounds in 
households is therefore not the ideal solution to the problem of reducing 
the population of dust mites. Liquid nitrogen has been used to kill dust 
mites in carpets by freezing, but use of liquid nitrogen is potentially 
dangerous and it must therefore be applied only by a trained technician. 
An alternative approach is the use of tannic acid, which denatures dust 
mite antigen but which does not kill the dust mites themselves. 
U.S. Pat. No. 3,973,011 to Bohner et al discloses organic oxadiazolyl 
compounds which are said to be effective pesticides against animal and 
plant pests. The oxadiazolyl compounds can be used alone or in combination 
with dispersants, such as alkali salts. 
U.S. Pat. No. 1,767,528 to Jones discloses a cleaning and disinfecting 
compound designed for household use, which contains common salt. U.S. Pat. 
Nos. 1,576,105 and 1,576,106 both to Fetherston disclose the use of sodium 
chloride for controlling the proliferation of microbes in garbage 
containers to reduce odors and other problems associated with decomposing 
garbage. 
U.S. Pat. No. 2,299,604 to Weirich relates to antimycotics containing 
sodium chloride for controlling athlete's foot. U.S. Pat. No. 191,476 to 
Seligman discloses a compound for disinfecting and deodorizing horse 
stables, which contains mineral salts such as potassium carbonate or 
potassium hydroxide. 
U.S. Pat. No. 088,300 to Jaycox discloses a flea powder which includes 25% 
abstract of Mentha pulegium (a plant commonly known as pennyroyal), 30% 
snuff, 20% Sinapis (a mustard) and 25% salt. The components are ground 
individually then uniformly mixed into a powder. Jaycox discloses that the 
degree of fineness of the ground components is immaterial in using the 
composition to destroy fleas. 
It should be noted that dust mites are as far removed from fleas, as human 
beings are from turtles. 
To be effective in reducing the population of dust mites, acaricidal 
compounds should be contacted on various substrates which accumulate 
mites, such as carpets, rugs, bedding materials, such as mattresses, 
blankets, bedspreads and pillows, upholstered furnishings and toys made 
from various fabrics, especially stuffed animals. Obviously, the 
acaricidal substances must not be allergens or irritants to persons coming 
into close proximity with such substrates, and who are allergic to house 
dust. 
The present invention uses common salt or its substitutes as inexpensive, 
environmentally safe acaricides. 
SUMMARY OF THE INVENTION 
The present invention is based upon the discovery that contacting 
substrates inhabited by dust mites with salt crystals as the active 
ingredient, kills and inhibits the proliferation of dust mites.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with the present invention, it has been found that contacting 
finely divided salt crystals on substrates inhabited by dust mites 
significantly reduces the number of live larval, nymph and adult dust 
mites. The salt crystals have been found to act as an acaricide to kill 
the dust mites. 
In treating the substrates inhabited by dust mites, the objective is to 
infiltrate the substrate environment with an acaricidally effective amount 
of salt. 
The size of the salt crystals should be such that they adhere to all areas 
of carpet or textile where the mites are present. The size must also be 
such as to efficiently produce an acaricidal effect by placing a maximum 
number of salt crystals in proximity to a maximum number of dust mites. 
Sodium chloride is readily available in granular, crystal and powdered 
forms. Granular sodium chloride consists of small pellets of salt. Crystal 
sodium chloride has the consistency of ordinary table salt, while powdered 
sodium chloride has the consistency of talcum powder. 
Although the mechanism of action of salt as an acaricide is uncertain, it 
is theorized that the dust mites, which are very susceptible to 
dehydration, are being affected by the change in osmotic pressure induced 
by the salt, with subsequent water loss from the dust mite resulting in 
its death. 
Other hygroscopic salts which can be used include potassium chloride, 
calcium chloride, sodium carbonate, ferric sulfate and potassium 
thiosulfate. The salt can be applied to the carpet or other textile or 
soft material substrate in finely divided form as 100% salt. 
Alternatively, the salt can be mixed with other active or inactive 
materials. 
The salt is applied in amounts sufficient to kill dust mites, which can be 
accomplished by evenly distributing the appropriate amount of salt over 
the substrate material and then contacting it throughout the substrate 
material, with such suitable means as a broom or brush so that it 
thoroughly infiltrates the substrate material. The salt is left to remain 
in place for about 1 to 2 weeks. It is then suitably removed by vacuuming. 
Salt applications can be repeated at intervals of about 2 weeks to 12 
months, preferably about 1 to 6 months and most preferably about 2 to 4 
months, depending on local conditions and the degree of mite infestation. 
A suitable amount of salt for substrates such as carpets and rugs can vary 
from about 1 to 1,000 grams, preferably about 10 to 500 grams and most 
preferably about 50 to 200 grams per square meter. Naturally, greater or 
lesser amounts of salt can be used, depending upon the extent of dust mite 
infestation. Beyond a certain point, an excessive amount of salt will not 
achieve a corresponding degree in the reduction of dust mite population in 
the substrate. It has been found that about 100 grams of finely divided 
salt per square meter of substrate is generally sufficient to kill a 
significant amount of dust mites on the order of about 90 to 99%. 
The following examples illustrate specific embodiments of the present 
invention. All parts and percentages are by weight unless otherwise noted. 
EXAMPLE 1 
Dust mites of the species D.pteronyssinus were grown in culture on 
TetraMin.RTM. brand fish food (Tetrawerke GmbH) at 75.degree. F. and 75% 
relative humidity for two to three months to establish a sufficient 
population. Approximately 1 teaspoon of cultured mites and food were then 
rubbed into sections of carpet measuring 325 square centimeters. Carpets 
were used in various size tufts from 1/4 inch to 3/4 inch. These carpet 
sections were then incubated under the same conditions for an additional 
three weeks. 
Seven sections of mite infested carpet were studied. Each section was cut 
in half. One half was treated with sodium chloride powder which was 
sprinkled on evenly and brushed in in amounts of 12.5 milligrams per 
square centimeter. The other half was left untreated as a control. Both 
halves of each section were then returned to the 75.degree. F. and 75% 
relative humidity conditions for an additional two weeks. 
At the end of two weeks, the mites in each section of carpet were counted 
by the "heat escape method." A sheet of clear adhesive faced plastic 
(Contact.RTM. brand self-adhesive covering, Rubbermaid Inc.) was placed 
adhesive side down on each section of carpet, and covered with opaque 
glass and a three pound weight. The thus prepared carpet was then placed 
upright on a hot plate (Fisher Scientific #11-498-7H). Using a surface 
thermometer, the temperature of the hot plate was increased by about 
1.degree. C. per minute, from an ambient temperature of 24.degree. C. to a 
temperature of 70.degree. C. over a period of approximately 45 minutes. 
The temperature was maintained at 70.degree. C. for an additional 15 
minutes. In an attempt to escape from the heat, the mites moved from their 
usual habitat deep in the carpet to its surface, where they became stuck 
to the adhesive covering. 
The adhesive sheet was then removed and overlayed upon a clear plastic 
grid. The sheet and grid were examined under a stereomicroscope, and the 
numbers of immature and adult mites in the center 25 square centimeters of 
each sample were counted. Table 1, which follows, shows the number of 
living mites in each treated and untreated section of carpet. 
TABLE 1 
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Number of Dust Mites 
Sample No. 
Untreated control 
Sodium chloride powder treated 
______________________________________ 
1 1073 29 
2 612 11 
3 472 27 
4 561 62 
5 1025 6 
6 2568 15 
7 683 80 
Mean: 999.1 32.8 
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The mean mite count in 25 square centimeter of the untreated halves of the 
carpet section was 999.1; the mean count in the treated halves was 32.8. 
These differences analyzed with a paired t-test were statistically 
significant at a p value of &lt;0.01. The mite counts were decreased on 
average by more than by 95%. 
EXAMPLE 2 
To compare the effects of salt having different particle sizes, 3 pieces of 
carpet, each approximately 500 square centimeters were labeled Samples A, 
B and C, respectively. Each sample was inoculated with cultures of D. 
pteronyssinus mites and incubated for three weeks, as described in Example 
1. Each carpet sample was then cut into three equal sections. One section 
of each sample was treated with powdered sodium chloride having the 
consistency of talcum powder. The second section of each sample was 
treated with crystal salt having the consistency of ordinary table salt. 
The third section of each sample was left as an untreated control. The 
amount of salt added was 12.5 milligrams per square centimeter, the same 
as in Example 1. After two weeks, the heat escape method detailed in 
Example 1 was performed and the number of mites per 25 square centimeter 
area were counted and tabulated in Table 2, which follows: 
TABLE 2 
______________________________________ 
Number of Mites 
Sample No. 
Untreated control 
Crystal salt 
Powdered salt 
______________________________________ 
A 320 232 71 
B 383 101 22 
C 135 192 11 
Mean: 279 142 35 
______________________________________ 
It can be seen that although crystal salt produced a decrease in the number 
of mites in two of the three samples, it was not as effective as the 
powdered salt, which decreased the number of mites significantly in all 
three samples. This indicates that the smaller more finely divided salt 
particles in powdered salt are a more effective acaricide in such 
substrates.