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In modern times most people spend more and more time in the home
environment, often working from home, so the causes of
allergies are more likely to be found there. Double glazing, central
heating, and fitted carpets are standard for most homes today, and
have provided the ideal habitat for the dust mite. The usual skin
tests performed are for mites, cats, dogs, other pets, and moulds in
damp houses, because these are the most common allergens in the
home. Although skin tests may indicate the most likely causes of an
allergic problem, these testing extracts, which are produced in
special laboratories to international standards, cannot relate
precisely to the allergens in the home environment of the individual
patient, so we all have our own personal environmental ‘
fingerprint’ which may differ considerably.
House dust is obviously a complex mixture of known and unknown
allergens containing vestiges of present and previous owners of the
house, their pets, their pests, and their habits. It is now
possible to analyse with great accuracy the amount of dust mite,
cat, dog, and an increasing number of other allergens in the house
dust of the patient, but these tests expensive and are mostly used
as a research tool. Although this is a great scientific advance, the
laboratory must be told which allergen to measure, and the
significance of the results.to the patient has to be assessed
clinically along with the other details of the case-history.
Dust may contain an unexpected allergen such as the recent finding
of large amounts of mouse allergen in dust from houses in New York
occupied by asthmatic children. Mouse is not a routine test, and
neither are tests for insects such as cockroach, which is very
uncommon here because they require a warmer climate. Cockroaches are
a common pest in the southern USA, and in some parts of Germany,
where allergy to cockroach has been recognised as a significant
problem. Other insects such as silverfish, ants, or fleas may
colonise houses, and tests may not be obtainable.
How to use the Peak Flow Meter to Investigate the Environment
The Peak Flow Meter can be a very useful instrument for investigating the
environment, and examples of significant Peak Flow charts are
shown below.

This patient was cured by the purchase of a new mattress
This is an extremely rare example from many years ago.
The cause was proved beyond doubt by carrying out a bronchial
provocation test with crude dust extract.
This case was seen before
the discovery of the dust mite

It was suggested by a consultant that this boy’s asthma in the holidays was
emotional in origin.
The old family house was very dusty with many dogs, but granny had a
new house with no pets where he stayed in the holidays. Note that a
weekend at home before he went to school produced an abrupt drop in
Peak-Flow.
This boy was at a rather Spartan boarding school with no carpets,
therefore fewer mites or animals.
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Chris was a severe asthmatic who had been thoroughly desensitised to
dust mite, yet he continued to have serious attacks. On admission to
the Derby Children’s Hospital for investigation he actually got
worse, and his mother noticed that the hospital still had feather
pillows, so she took him home. Although skin tests were
negative for feathers, his mother, without being instructed to do
so, carried out an improvised provocation test by having him inhale
from a paper bag in which there were a few feathers, with such an
obvious result that he had to have a short course of steroids, as
shown above. She then showed that his peak flow would fall within
minutes of sitting on a feather stuffed sofa, proving that feathers
were also a significant allergy. The peak flow chart shows how
removal of all feathers from the house had a dramatic effect on his
peak flow, he was soon a member of the Nottingham High School rugby
team, and has been well since. I was somewhat taken aback by
mother’s approach to this problem, which I would never have dared to
suggest, but she got the answers!
Allergy to a vaccine
grown on chick embryo
Allergy to feathers is not common, and can be associated with
allergy to eggs or chicken. A patient was referred complaining of
attacks of asthma every Sunday since he had had his flu vaccine
injection, which is grown on chick embryo. The reason was that he
normally had chicken for Sunday lunch, yet he had eggs for breakfast
every morning without any effect, but with avoiding chicken he had
no more asthma.
At the present time it is considered that skin reactions to feather
extracts are probably due to the fact that feathers are often
infested with mites. Skin reactions are very rare, and feather
allergy is very uncommon, but it does exist occasionally.
Wool used to be on everybody’s bed, and allergy to wool did occur, but have
been substituted by duvets stuffed with down or a variety
of synthetic materials which can become infested with mites. I once
saw a young man who had asthma from November to April every year. He
had a very positive skin reaction to cotton, with which his duvet
was stuffed, and after he changed it he had no more asthma. I have
never seen a similar case, but cotton stuffed bedcovers are still
used by ethnic minorities.

In this case the patient always saw her doctor in the evening, and
he did not believe that she had asthma because her peak flow was
always 600.
When she was given her own meter it was found that in the early
morning the peak flow was only 60. On further investigation the
cause was found to be dust mite, and she was much improved with a
new mattress and desensitisation. This was before the days of
inhaled steroids.

Investigating Dust from the Patient’s own Environment
Crude extracts of house dust were used for skin testing and
treatment for many years before the discovery that the dust mite was
the major allergen.
Many twenty years ago I saw a patient who
complained that when he sat in his favourite armchair every evening
looking at television he got uncontrollable sneezing fits, but at no
other time or place. His skin tests were very positive for dust
mites, so I asked him to bring samples of dust from his bed, his
chair, and a general sample in separate vacuum cleaner bags. I mixed
a little fine dust from his chair dust sample with a drop of water
and pricking through it produced a very impressive reaction much
larger than those produced in the same manner using the other dust
samples as a skin test. He threw away the chair, which must have
contained enormous numbers of mites, and his problem was solved. A
nice neat easy solution!!!
This amusing case suggested that this crude test could be developed
into a useful method of investigating the environmental challenge.
The droppings of the dust mite, the major source of mite allergens,
are quite small, so dust samples have to be sieved to get rid of the
fluff etc., so I improvised a dust shaker from an old electric razor
attached to a very fine sieve from a Japanese tea stariner. 100 mgms of sieved dust was
weighted out, placed in a 2ml disposable syringe with a disposable
sterilising filter attached, and 1 ml of saline added. After a few
minutes this mixture was pushed through the filter to remove any
bacteria from the extract. A few drops of this crude extract are
more than adequate for a skin prick test and, if positive, the reactions demonstrate to
both patient and doctor the importance of their
home environment.
This is how my environmental dust test for individual patients was
developed, and ever since has provided invaluable information on the
relationship between patients and their home environment. The skin
reactions produced are often impressive, as in the case shown above
right where an extract of the patient’s house dust produced a
reaction as big as a very special laboratory extract made from a
pure mite culture to an international standard of potency.
Using a similar technique the hairs of any pet animal can be used to
produce an immediate testing extract. The reactions produced can be
bigger than the reactions produced by the standardised commercially
produced testing extracts, and as some breeds of dogs are more
allergenic than others using the hair of the family pet makes sense.
A reaction can also be produced by rubbing pet hair into the skin.
These procedures can strongly reinforce advice to find the pet a
good home by showing the effects on the patient’s own skin.
The environmental dust test can be repeated after using an acaricide,
or following the departure of the pet and a spring cleaning, to show
if the amount of allergen in the dust has decreased.. This method is
much cheaper and quicker than the scientific method, as the dust
sample does not have to be sent off to a distant laboratory, and the
results are available in a few minutes. The photo on the left is a
good example, as the biggest reaction is to home dust extract. This
patient had had two years severe asthma, worse at home where there
was a dog and a hamster to which skin tests were only slightly
positive, but negative to mites, suggesting another cause. The
patient was using a carpet shampoo cleaner twice a week, as she was
mad about cleaning, When the cleaner was stopped the asthma ceased,
except on one occasion when she arrived home shortly after her
husband had used the carpet shampoo and had a severe attack.
I had actually considered the hamster to be most likely answer as,
in another case, asthma every night was caused by the dander from
the hamster in the warm kitchen below floating up to the bedroom
above. The removal of the hamster was curative, but the diagnosis
was suggested by the case history, as usual.
The intensity of skin reactions to extracts of environmental dusts
vary greatly, sometimes being more intense than reactions to very
expensive testing extracts made from mite cultures in laboratories
under strictly controlled conditions. A negative mite test and a
positive reaction to the patient’s own dust extract clearly
suggests that an allergen other than mites is present in the dust
and is the cause of the problem.
 On the left the reaction at the top is to the dust extract when the
cat was still present in the house, and the lower one from the dust
a year later when most of the cat allergen had gone and the patient
no longer had a problem. There was no reaction to dust mite.
On right extracts from long and short haired cats are compared
showing that the long haired cat is much more allergenic.

Measuring the speed of release of allergens from dust
Any dust allergic will tell you that a trace of dust will trigger
sneezing in a very short time, just as grass pollen does. This fact
suggests that the allergen from dust or pollen is dissolved out very
quickly when pollen grains or particles of mite excreta are inhaled
and settle on the moist surface of the eye, the nose,
or the bronchial tubes. Many years ago I attempted to measure how
quickly the allergen is released from pollen on wetting by plunging
one of my special needles holding a drop of saline on the point into
a tiny heap of pollen on the forearm of a pollen sensitive
volunteer, then wiping it all off with a big pad of wet toilet
tissues as quickly as possible, while timing this with a stopwatch.
Even when wiped off in just under one second the skin reaction to
the pollen was very large indeed, so I wondered if the allergen in
dust would be released as quickly as the pollen.
The set-up illustrated above consisted of a 1ml plastic syringe and
needle containing saline to extract the dust. There was a contact on
the end to switch on the stopwatch when the saline was injected
through the rubber piston of the 2ml syringe which contained a
measured amount of fine house dust, and neatly accommodated the 1 ml
syringe. Thus the saline was injected into the dust, extracted, and
after 2, 5, and 10.seconds, and 30 minutes, as shown, was pushed
through the filter on the end of the 2ml syringe. The stopwatch
would stop when pressure was released, thus giving the time of
extraction.
On the right is a photo of skin reactions to these timed extracts,
using my standardised disposable needles, which show that some
allergen was extracted in 2 seconds, a little more in 5 seconds, a
considerable amount in 10 seconds, and not a great deal more in 30
minutes. The photo above is the result of electrophoretic analysis
by Dr Terry Merrett of extracts which correspond to these skin
reactions and confirming that important allergens which can cause
symptoms are extracted in seconds

Microscopical Examination of House Dust samples
These experiments led to an interest in closer examination of house
dust, the living environment of the mites, which very rarely seen in
dust because they shy away from light. Bed dust is mainly composed
of skin scales which provide a rich food source for the mites. It is
said, but I cannot find the authority or imagine how the figure was
arrived at, that we each shed at least 750 Gms of skin a year.
Eczema sufferers must shed much more skin to feed the mites which
produce droppings containing the powerful allergen which is often
the cause of their eczema, thus forming a very vicious circle. These
skin scales can also be seen in a sunbeam or the ray of light from a
projector and are always present in the air in any inhabited
building. They provide a means of transmission of
infection, as demonstrated by this picture of a skin scale stained
to show the bacteria it is carrying.
Under
the microscope house dust contains grit carried into the house on
shoes, fibres of all sorts from carpets and other furnishings, human
and pet hairs, and skin scales. The most significant sample is from
the bed, the bedding, the mattress, and the floor around the bed,
because this is the dust that has the closest contact with the
patient, who spends a large part of his or her life in this personal
environment. General dust is obviously less important, but if
symptoms are worse on a certain sofa or chair then separate samples
can be most helpful.
The major allergens of the dust mite are concentrated in the faecal
particles, especially in the membrane which covers them like a
little bag. The mites are rarely seen, but the faecal particles can
be distinguished with difficulty by using a cotton blue stain, and
making sure that the layer of dust on the slide is as thin as
possible. These particles are a little bigger than a pollen grain,
so that when they become airborne they settle fairly quickly, unlike
cat dander which is so small and light that it can remain in the air
for days. The faecal particles are still difficult to distinguish
from dirt while the microscope light is coming from below, but by
illuminating the specimen with light from the side, supplied by an
adjustable fibre-optic light, they are easily seen and are quite
distinct from the dirt particles and skin scales which are the main
constituents.
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Mite about 0.20 mm long with
faecal particles
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Dust from a 50 year old
mattress
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Faecal particles X 400
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Faecal
particles from bed of eczema patient
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A mite
egg in culture
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A
faecal particle X400 lit from the side
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On the left the dust is illuminated from below, and the faecal
particles are difficult to distinguish from dirt.
When illuminated from the side the particles can be easily
identified and the degree of contamination of the dust with mite
faeces, which are white, can be roughly assessed
This dust specimen
(right) is from the bed of an eczema patient in 1988
which had been stored in a tube at room temperature and examined
again in 2004. It is evident that the mite faecal particles are
still there in abundance 23 years later.
The remarkable improvement
in his eczema after getting rid of the mites by using an acaricide
is shown in the Acarosan section.
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