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Prepared by Dr. M. Yadav,
Consultant Allergist of a private hospital in Kuala Lumpur. Dr. Yadav can
be contacted at telephone number - 03-22828795
(Dr. M. Yadav was former
Professor in Immunology in the Department of Genetics and Cellular Biology,
Universiti Malaya. He has published over 200 research papers on various aspects
of allergy and immunology in international journals. He has worked in many
parts of the world and received several awards. He currently manages an allergy
testing and diagnostic service at Pantai Medical Centre. His book entitled
'Causal Triggers of Allergy and Asthma' is expected to be released in 2004.
Here he explains the nature of allergy, what tests need to be performed to
diagnose the trigger factors and how to manage the problem over long terms)
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What
is allergy?
An allergy is an abnormal exaggerated physical reaction (with development
of any of the following symptoms: diarrhea, vomiting, skin rashes, hives,
sneezing, runny nose, asthma, chronic cough, joint pains, puffiness of
the eye orbit or face, ear infection, anaphylaxis) to one or more substances
called allergens that are harmless to most people. Skin, oral and nose
allergy symptoms are associated with intense itch. Sources of common allergens
that trigger the allergy symptoms include house dust mites, plant pollens
(called hay-fever in temperate regions during spring/summer) mould spores,
pet dander (skin scales from pets), foods (for example eggs, peanuts,
cows milk, shrimps and many others), drugs (for example penicillin, sulphonamides),
venom of stinging insects (for example mosquito bites, wasp sting, ant
sting) perfumes (both naturally derived from flowers and artificially
synthesized), and many others. Frequent exposure to the provoking allergen
will trigger the development of allergy symptoms. Individuals with allergy
often have a genetic predisposition with a strong family history of the
disease.
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What
is the mechanism of allergy?
In allergy suffers the immune system produces large amounts of an antibody
called Immunoglobulin E (IgE) as part of a confused defense strategy against
harmless allergens. Normal individuals do not produce IgE antibody following
exposure to allergens. The IgE antibody to the specific allergens enters
the blood circulation and distributes to all parts of the body. The IgE
antibody has a natural tendency to bind to mast cells present in the skin
and mucosal tissues because these cell have special anchoring points for
IgE molecule on their surface. Each mast cell may have half-million IgE
antibody molecules attached on its surface. Such a person is said to be
sensitized to the specific allergen and is ready to react to the allergen
on further contact with it. The interaction between the IgE molecules-on-the-mast
cell and the allergen causes the mast cell to release powerful chemical
mediators (such as histamine, leukotrienes, cytokines and others) that
immediately cause inflammation and rash at the site. Thus, two conditions
are necessary for allergy to occur: (1) An acute IgE-mediated hypersensitivity
to allergens, and (2) Recurrent or continuous exposure to the specific
allergen. The absence of either causes the allergy to disappear. In contrast,
the taking of medication merely suppresses the symptoms of allergy.
Therefore, the quantities measurement of total IgE levels and allergen-specific
IgE antibodies is the key to effective diagnosis and management of allergy.
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What
are the symptoms of allergy?
Allergic symptoms usually appear on the skin and the mucosal surfaces
since these tissues are (1) the first to come in contact with the allergen,
and (2) also the mast cells are found in large numbers here. Allergy symptoms
can take many different forms depending on the reaction of the target
organ. Some allergy symptoms are listed below:
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Nose:
Allergic rhinitis is 'flu-like' and associated with nasal itching, congestion,
sneezing, runny thin watery discharge and postnasal-drip. Sinusitis with
headache, facial pain, purulent discharge, is often a complication of
rhinitis. Chronic rhinitis may be associated with puffy dark circles underneath
the eyes. The triggers in Malaysia are house dust mites and pet dander.
Sometime pollens may be involved but are the main seasonal triggers in
the temperate regions causing hay-fever. Food allergens can also provoke
the symptoms and complicate diagnosis.
Eyes: Allergic conjunctivitis is associated with itching,
redness, swelling and tearing of the eye. The common triggers are house
dust mites, pet dander, bird dropping and feathers and pollens. Foods
may also be involved.
Lungs: Asthma symptoms are shortness of breath, wheezing,
feeling of tightness in chest and cough. Frequent bronchial infections
may be caused by allergy. Airborne allergens (such as, house dust mites,
pet dander, bird feathers, perfumes) are the main triggers of IgE-mediated
asthma but certain foods may worsen the condition. Some foods such as
cows milk may trigger the asthmatic attack in sensitized children.
Skin: Hives (urticaria) are itchy welts of varying sizes
that appear on the skin, lips, inside the mouth and ears. Sometimes there
is swelling in the affected parts resulting in symptoms of angioedema.
Eczema (atopic dermatitis) is an itchy rash that appears in the skin creases
of the arm, leg and neck but may be present in all parts of the body.
Foods often play an important role in the development of the condition.
Airborne allergens like house dust mites may also participate in the condition.
Lately it has been noted that some fungus species that are naturally present
on the skin may also be responsible for the development of the skin symptoms.
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Digestive tract: Food allergy symptoms may be associated
with stomach cramps, vomiting and diarrhea. Food allergy may also be responsible
for eczema, asthma, chronic rhinitis, ear problem, gastrointestinal distress,
headache, fatique, hyperactivity and depression. In rare instances foods
may cause a life-threatening systemic response called anaphylaxis. For
instance peanut allergy can be so severe in some children and adults that
it results in anaphylactic shock.
Ears: Symptoms of recurrent infection or fluid in the
middle ear can be provoked by allergic reaction and eventually result
in loss of hearing. Both airborne allergens and food allergy can plays
a role in many instances.
Emotional factors: Although allergy is a physical disorder it can be aggravated
by intense stress, fear, anxiety, anger, extreme aggravation, and other
emotional strains.
Additional provoking factors: Some irritating substances
like tobacco smoke, paint solvent, vehicle exhaust, diesel fumes, strong
perfumes, chlorine in swimming pools and other chemicals can act as promoters
of allergy and worsen the symptoms in many instances.
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There are two types of allergy
test available:
(1) Skin Prick Test, and
(2) Allergy Blood Test,
based on 'Cap RAST' performed on a blood sample.
Skin Prick Test: In this test small drops of allergens in variable concentration
is placed on the forearm and the dermis punctured with a special lancet. The
development of a raised area (called wheal) similar to a mosquito bite appears
within minutes and the area surrounding the wheal becomes reddened (flare).
The response is compared to negative and positive controls run at the same
time. A positive reaction for the allergen is confirmed when the swelling
reaches a certain size which is bigger than the negative control.
This test has many limitations. Skin testing is dangerous in highly sensitive
patients and there have been fatalities recorded in the past. Patients must
stop taking anti-histamines for at least 7 to 28 days (depending on drug)
because the drug suppresses the skin reaction causing the development of a
false negative result. The skin test is not useful for babies and the elderly.
In general skin tests are not useful indicators for food allergies because
of the frequent false positive reactions. Skin testing is being rapidly replaced
with allergy blood testing.
Allergy Blood Tests: There are many types of cheap allergy blood testing methods
available but most of them have poor reproducibility. Moreover, these tests
normally report the results with fancy colourful charts which appear impressive
but provide little information to the professionals. These tests often give
false positive or false negative results that may cause more harm than good.
In general, hospitals worldwide do not use these types of allergy testing
methods but use the cap RAST technique as the only method of choice.
The Cap RAST method uses a state-of-the-art technique that is accepted world
wide as the in-vitro Gold Standard. Moreover, the IgE level estimated by the
equipment is standardized against the World Health Organization immunology
standards for IgE maintained by them. The cap RAST reports the results in
both quantitative and qualitative terms for professional assessment. Therefore,
the allergy blood test using the cap RAST is the method of choice because
it is sensitive, accurate, safer, convenient and unaffected by medication
taken by the patient. The allergy blood test can be performed in babies and
elderly and in persons with severe eczema in whom it is difficult to do the
skin test.
The choice of the allergens selected for test depends on the clinical history.
Usually the doctor may select about 12 to 15 allergens based on his experience
but in some cases he may select less allergen for testing. Skill and experience
is required to interpret the result and in most cases the test results often
fit the clinical observation and confirm the diagnosis. Appropriate avoidance
measures should be immediately implemented. The benefits of the avoidance
measures usually become apparent within the first few days.
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Can
the risk for allergy be determined at birth?
It is now possible to identify babies at risk for allergy at birth. Two
factors are usually considered, namely (1) Family history, and (2) Cord
blood total serum IgE level. Epidemiological studies have shown that when
one parent has allergy the risk for the baby is 20 percent but if both
parents have allergy the risk for the baby developing an allergic disorder
increase to 70%. The risk of allergy is four times higher if the mother
has allergy compared if the father has allergy. If there is a family history,
even when grandparents have allergic symptoms, it is advisable to plan
to reduce exposure to allergens for the baby even during the pregnancy.
In recent years research studies have revealed that the foetus develops
in an immunological environment biased for the humoral response during
pregnancy. This means that genetically predisposed foetus has a very high
risk for being sensitized to allergens during pregnancy. This means that
the serum IgE levels will be elevated in the baby's blood. Thus, the risk
for allergy can be easily determined by estimating the total serum IgE
level in the cord blood at birth. A high IgE concentration in the cord
blood suggests that the baby has a high risk for the development of allergy.
This information pre-warns the paediatrician of the possibility of allergy
symptoms in the baby appearing anytime after birth depending on the exposure
to allergens. Therefore, avoidance measures can be taken early even before
the symptoms appear and reduce the chances for allergy symptoms in the
predisposed baby.
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At birth an infant's immune system is immature and the
neonate is dependent on many factors present in breast milk for immune protection.
Depriving the baby of breast milk may speed up the development of allergy
in pre-disposed infants.
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The
Allergy March
Young babies who develop food-induced eczema before one year have almost
50 percent risk of developing asthma by age 5 years. This is specifically
true of babies who have been exposed to high levels of house dust mite
allergens. Another study revealed that children who wheeze before age
3 years and continue to wheeze at age 6 years have diminished lung function
and a 2- to 3-fold increased risk of having asthma at age 11 years. These
studies indicate that intervention for asthma must be initiated very early
in childhood to change the course of history of the disease.
In predisposed infants in the first few months the initial symptom of
allergy manifest in the skin as eczema and the severity of the symptoms
slowly decrease with age giving the impression that the allergy is getting
cured. Often the eczema is followed by allergic disorder of the gastrointestinal
tract and when it appears that the symptoms are disappearing respiratory
allergic disorder begins. The respiratory allergy initially manifest as
rhinitis but soon followed by wheezing often ending up as asthma. This
is called the Allergy March. Do not ever be complacent when the child
develops an allergic symptom in early life. Immediately find the cause
and manage it through avoidance. Early in life management of the allergy
will prevent the child developing asthma later in childhood.
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What
are the benefits of breast milk?
Breast milk is unique and is the ideal food for the baby. It fosters proper
growth to the newborn. The composition of human breast milk among others
includes nutrition, growth factors, hormones, enzymes, blood cells that
fight infections and immune-protective factors. The lactation is robust
and mother's breast milk is adequate in essential nutrients, even when
her own nutrition is inadequate. Mature breast milk usually has constant
levels of about 7g/dL carbohydrate and about 0.9g/dL proteins. But the
composition of fats essential for neonatal growth, brain development,
and retinal function varies according to a woman's intake, the length
of gestation, and the period of lactation. Vitamins and minerals also
vary according to maternal intake.
However, even when these
nutrients are lower in breast milk than in formulas, their higher bioactivity
and bioavailability nearly meet the complete needs of neonates than provided
by even the best infant formulas. Also, in many instances human milk components
compensate for immature function, such as a neonate's inability to produce
certain digestive enzymes, immunoglobulin A (IgA), taurine, nucleotides,
and long-chain polyunsaturated fatty acids. In addition, the breast milk
contains various cells (such as macrophages, neutrophils and lymphocytes)
that play a critical role in the immune protection of the baby.
Babies on breast milk
have lower risk for the development of allergy. Human milk lacks inflammatory
mediators, and contains anti-inflammatory agents such as antiproteases,
antioxidants, and enzymes that degrade inflammatory mediators and modulators
of leukocyte activation. Furthermore, IgE (the principal immunoglobulin
responsible for immediate hypersensitivity reactions), basophils, mast
cells, eosinophils (the principal effector cells in these reactions) are
absent in breast milk. The mediators from these cells are also absent
in human milk. Immune and nonimmune protecting agents are present in milk
throughout lactation and some, such as lysozyme, are present at higher
concentrations during prolonged lactation than during the early stages.
Therefore, although it is advocated that breast-fed infants receive food
supplements after 4 to 6 months of exclusive breast-feeding, it is advisable
to breast-feed for longer periods.
Moreover, the breast milk promotes the development of healthy gut flora
that acts to suppress the development of the allergic reaction.
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What
is the alternative to breast feeding?
If possible the babies should be breast fed. However there are many mothers
for one or other reasons cannot breast feed their babies. There is wide
range of cows milk formulas' available. Until recently there was not much
difference between these cows milk formulas. Nowadays various components
are added, for instance essential fatty acids, healthy bacteria and vitamins
to competitively market these foods. Nonetheless, since cow's milk, a
highly allergenic food, is the first foreign protein given in large quantities
to the newborn baby, it is not surprising to find cows milk is the major
cause of milk allergy in about 10% of the infants.
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Recently, a new infant formula containing partially hydrolyzed cows milk whey
formula (Nan HA) has been introduced. The highly allergenic proteins in the
cows milk have been treated enzymatically to make them less allergenic. Over
20 research studies throughout the world including Singapore, demonstrates
that this hypoallergenic formula significantly reduces the development of
allergy. The use of partially hydrolyzed whey formula in infants for the first
four to six months of life significant reduced the manifestations of allergic
diseases for 5 to 10 years. In a study performed in Singapore a significant
reduction in atopic disorders at 12, 24, 36 and 60 months was found in infants
who were on partially-hydrolyzed hypoallergenic milk formula for 4 months.
These observations suggest long term benefits detectable way past the period
of direct intervention with the partially hydrolyzed milk formula. Some studies
have suggested that partially hydrolyzed cows milk formula should be preferentially
introduced for at least 4 months to all babies if the infant's mother opts
not to breast feed.
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Can
totally breast fed babies develop severe allergy symptoms?
In a family with a history of allergy special care is needed to avoid
allergens during pregnancy and also during the early development of the
baby. Even babies who are totally breast fed can develop allergic reactions.
Food allergens in the mother's diet can appear in her breast milk within
2 to 6 hours. Even aeroallergens such as pollen allergens and house dust
mite allergens that the mother is exposed to can appear in the breast
milk. The allergens in the breast milk can sensitize the baby or provoke
symptoms in babies who are already sensitized. Allergy symptoms can develop
in predisposed infants continuously exposed to food allergens or aeroallergens
in breast milk.
Previously, several allergy symptoms including regurgitation, vomiting,
colic, diarrhoea, and eczema have been reported in breast feed infants.
Elimination of the offending food allergens from the mother's diet corrected
the symptoms in the babies. In Malaysia we have found allergic skin reaction
in exclusively breast fed infants. We tested the infant's blood for specific
IgE antibodies to common foods in the mother's diet. We have found IgE-mediated
response to cows milk, eggs, and wheat in different infants. In one infant
with severe allergic disorder of skin the IgE antibody response in the
baby was directed to many allergens in the mother's diet. Thus parents
need to be aware of the possibility of allergy symptoms developing in
their infant via the breast milk particularly in families with a history
of allergy. We recommend that special dietary precautions be taken during
lactation for mothers of high-risk families.
In North Europe many parents with history of allergy plan their babies
so that the later part of the pregnancy and early lactation falls outside
spring and early summer when the air pollen counts are high to reduce
exposure to pollen allergens.
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Allergy
to house dust mites
House dust mites are the most common cause of asthma, allergic rhinitis and
sometimes eczema. In Malaysia, house dust mites are found in all localities
surveyed with 80% homes containing several species of mite in high numbers.
In one Malaysian study, millions of mites were found multiplying in the mattresses
of most homes throughout the country. The two most prominent house dust mites
found locally are Blomia tropicalis and Dermatophagoides pteronyssinus. These
two species have unique allergens that do not cross-react and should preferably
be tested separately in a patient suspected of house dust mite allergy. About
85% of patients allergic to dust mites react to both species but the other
15% react to one or the other species.
Dust mites feed mainly on skin scales (derived from humans or mammalian pets),
fungi, hair/fur and body fragments of dead insects. The life span of the adult
mite is about 2 to 3 months and during this period it will lay about 50 eggs
per month. These eggs hatch and mature in about twenty-five days in the tropics.
The major allergen of the house dust mite is derived from the fecal pellets
(each dust mite defecates about 50 pellets daily) and dead dust mite parts.
The fecal pellets are about 20 microns in size and can reach the upper airways
of people breathing them. Fecal allergens contain enzymes that allow the allergen
to penetrate mucosal surfaces rapidly and cause immune allergic sensitization.
Exposure to high levels
of house dust mite allergens during infancy increases the risk of allergic
sensitization and the development of asthma in later life. In Malaysia about
90% of children with asthma or allergic rhinitis are positive for house dust
mites. In adults with asthma the prevalence rate of mite sensitization is
close to 70%. Many adults with non-specific chronic cough are often positive
to house dust mite allergens. Many patients with eczema also react to house
dust mites. All patients with asthma or allergic rhinitis should undergo allergy
tests for house dust mites to identify the causal factors for long term management
of their clinical symptoms. Many studies have emphatically demonstrated that
reduction of exposure to the mites in the home environment significantly lead
to the improvement of allergic symptoms. One company in Malaysia has experience
in home management of house dust mites. They also supply allergy products
(mattress/pillow allergicovers, anti-dust mite sprays and air-filters.)
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