  
|  |
|
|
|
Reviewed by Dr Paul Klenerman, specialist and Professor Brian Lipworth, professor of allergies and respiratory medicine
|
What is house dust mite allergy?
House mite allergy is a hypersensitive reaction to proteins in
the excretion of dust mites. The protein attacks the respiratory passages
causing
hay fever and
asthma. It will
aggravate
atopic dermatitis in
people who have a tendency to this problem.
House dust mites are found in all homes. They are microscopic
organisms that thrive in warm and humid houses with lots of food - human skin.
The mites prefer to live in beds and, because we spend about a third of the day
in bed, we inhale large quantities of dust mite allergens.
How do you become allergic to house dust mites?
The excretion of the mites contains a number of protein
substances. When these are inhaled or touch the skin, the body produces
antibodies. These antibodies cause the release of a chemical called histamine
that leads to swelling and irritation of the upper respiratory passages -
typical asthma and hay fever symptoms. The predisposition for allergy is often
hereditary.
Unlike pollen, dust mites are present all year round causing
constant allergy - 'perennial' allergic rhinitis. The excretion from
the mites dries out and can be launched into the air when someone walks over a
rug, sits down in a chair, or shakes the bed clothes, giving allergic people
immediate symptoms.
What are the symptoms of house dust mite allergy?
-
Hay fever, runny
nose, itching, sneezing.
-
Watering eyes.
-
Asthma, difficulty in
breathing.
-
Infantile eczema (a
skin disease) may get worse.
What makes the symptoms worse?
-
Air pollution such as tobacco smoke or car fumes.
How does the doctor make the diagnosis?
It is often enough to tell the doctor when, where and how you
get the symptoms. Skin tests and various
blood tests can be
used for confirmation.
Good advice
It is best to do everything possible to avoid hypersensitivity
to house dust mites. People who have perennial rhinitis, inflamed mucous
membrane of the nose, or are allergic to house dust mites should try to adapt
their homes.
-
Have as little furniture as possible in which mites can
live.
-
Clean walls, woodwork and floors with wet cloths. The floor can
be polished.
-
Only use rugs that can be washed once a week.
-
Use bedding that can be washed often, cotton sheets, washable
bottom sheets and synthetic blankets or duvets. Don't use woollen blankets
or quilts.
-
Make sure your chairs are made of wood or plastic.
-
If you can, use plastic curtains and dust them daily.
-
Use wet cloths and a vacuum cleaner with a no bag vortex and
allergen filter to clean the house thoroughly, preferably every day, but at
least twice a week.
-
Avoid dust traps like teddy bears, cushions, dried flowers,
bric-a-brac and toys.
-
Wash bedding etc at a temperature of at least 60°C to kill the
house dust mites.
-
Leave bedding, duvets, pillows and mattress hanging outside for
an hour every day or as often as practical.
-
Put duvets and pillows in plastic bags and put them in the
freezer for 24 hours at least once a month.
-
You may want to sleep on a cheap mattress that you can exchange
for a new one at least every six months.
-
Dust mites hate dry and cold air, so try to air the house every
day and don't use an air humidifier, which will only make matters worse.
If the lower edge of the window is moist when you wake up in the morning, there
is too much humidity in the air.
-
Do not spray the house, it may worsen your symptoms.
-
Do not touch dusty objects like books and old clothes.
-
When you are likely to be exposed to substances that give you a
reaction, eg when you are house cleaning, you should wear a mask.
-
Don't allow smoking in the house.
What complications are possible?
-
You are predisposed to other respiratory diseases.
-
You are also predisposed to
otitis, inflammation
of the ear.
-
You may have
trouble sleeping and
suffer from chronic fatigue.
-
Hospitalisation following a severe
asthma attack.
Future prospects
If you are allergic to house dust mites, it is important that
you don't expose yourself to the dust mite allergen because it increases
your chances of developing asthma. The best remedy against house dust mites is
described under the heading 'Good advice' above.
Your symptoms can be controlled by treatment, but you can't
escape your hypersensitivity. If severe dust mite allergy is the only form of
allergy you suffer from, your doctor may want to try hyposensitisation - a
'vaccination' against the allergen. This tolerance treatment involves
regular allergen injections in increased doses over a period of five years, but
is not routinely given and is not always successful.
What medicine is given?
Medicines for allergies include:
-
Antihistamine
tablets or syrup (eg
loratadine,
cetirizine). These
lessen the allergic reaction by blocking the actions of histamine. They relieve
hayfever symptoms.
-
Nasal sprays or drops containing
sodium
cromoglicate, corticosteroids (eg
beclometasone) or
antihistamines (eg
levocabastine). These can
be used to reduce nasal inflammation and control symptoms in the
nose.
-
Eye drops containing
sodium
cromoglicate, nedocromil, or
antihistamines (eg azelastine) reduce
eye inflammation and can be used if eye symptoms are a particular problem.
If the allergy causes asthmatic symptoms, some of the asthma
medication below may be used
-
Relievers (bronchodilators): these are
quick-acting medicines that relax the muscles of the airways. They are used
when required to relieve shortness of breath.
-
Preventers: these act over a longer time
and work by reducing the inflammation within the airways. They should be used
regularly for maximum benefit. When the dosage and type of preventive medicine
is correct, there will be little need for reliever medicines.
Relievers
There are three groups of bronchodilators.
Beta-2 agonists
Beta-2 agonists cause the airways to
relax and widen. Examples of those which act for a short time (3 or 4 hours
following a single dose) are
salbutamol and
terbutaline. These
medicines are inhaled from a variety of delivery devices, the most familiar
being the pressurised metered-dose-inhaler (MDI). When inhaled, these types of
medicines work within minutes to open the airways, making breathing
easier.
Longer-acting beta-2 agonists include
salmeterol and
formoterol. Their
action lasts over 12 hours, making them suitable for twice daily dosage to keep
the airways open.
Anticholinergics
One of the ways in which the size of the airways is
naturally controlled is through nerves that connect to the muscles surrounding
the airways. The nerve impulses cause the muscles to contract, thus narrowing
the airway.
Anticholinergic medicines such as
ipratropium block
this effect, allowing the airways to open. The size of this effect is fairly
small, so it is most noticeable if the airways have already been narrowed by
other conditions, such as
chronic bronchitis.
Theophyllines and aminophylline
Theophylline and
aminophylline are
given by mouth and are less commonly used in Britain because they are more
likely to produce side effects than inhaled treatment. They are still in very
wide use throughout the world.
All three types of reliever can be combined if
necessary.
Preventers
There are three main groups of anti-inflammatories.
Corticosteroids
Corticosteroids (or
'steroids') work to reduce the amount of inflammation within the
airways, reducing their tendency to contract. They are usually given as inhaled
treatment, eg
beclometasone, although sometimes oral steroid tablets may be required for severe
attacks. Although steroids are powerful medicines with many potential side
effects their safety in asthma has been well established. It is also important
to balance the problems that arise from poorly treated asthma against the
improvement in health which occurs when the condition is well treated.
Cromones
There are two kinds of
cromones:
sodium
cromoglicate and
nedocromil. They
also act to reduce inflammation of the airways. They tend to be best for mild
asthma symptoms and are more effective in children than adults. The medicines
are given by inhalation and are usually very well tolerated.
Leukotriene receptor antagonists
Leukotriene receptor antagonists are
compounds released by inflammatory cells within the lungs and which have a
powerful constricting effect upon the airways. By blocking this effect with
these antagonist medicines the constriction is reversed. There are two such
medicines currently available:
montelukast and
zafirlukast.
Most cases of allergic asthma are best controlled with an
inhaled
corticosteroid, eg beclometasone,
which is taken at regular intervals as a preventative measure. A beta-2
agonist, eg salbutamol, is used in conjunction with this to relieve symptoms
when necessary. For patients who have associated perennial or seasonal allergic
rhinitis (hay fever) the use of an antihistimine, eg cetirizine, is often useful.
|
Based on a text by Dr Flemming Andersen
|
Last updated 04.01.2005
|
 |
|
|
 |
| |      |
|
