What is allergy?
Allergy is not a disease itself, but a mechanism leading to a disease. Or an immunological hypersensitivity that can lead to a variety of different diseases via different patho-mechanisms with different approaches in diagnosis, therapy and prevention.
Allergy therefore presents as a number of diseases.
Cool got it
any substance stimulating the production of IgE or a cellular immune response. Allergens are usually proteins, but not always. They can for example be carbohydrates.
Normal response to a stimulus.
Abnormally strong response to a stimulus.
Production of IgE antibodies (detected by serum IgE assay or SPT) after repeated exposure to an allergen.
A hypersensitivity reaction initiated by specific immuno- logical mechanisms. This can be IgE mediated (e.g. peanut allergy) or non-IgE mediated (e.g. milk allergy).
A tendency to produce IgE antibodies in response to ordinary exposure to potential allergens. Strongly associated with asthma, rhinitis, eczema and food allergy.
A serious allergic reaction with bronchial, laryngeal and cardiovascular involvement that is rapid in onset and can cause death.
A substance, whether processed, semi-processed or raw, which is intended for human consumption (including drinks), and any substance used in the manufacture, preparation or treatment of food.
Immunologically mediated adverse reaction to food.
How does allergy present?
Via Major allergic diseases
List the major allergic conditions (8)
1. rhinitis or hay fever 2. conjunctivitis 3. asthma 4. Atopic dermatitis or eczema 5. Urticaria 6. Insect allergy 7. Drug allergy 8. Food allergy
What is the predominant pre-school allergic conditions?
eczema and food allergy
Which diseases r rare in young children & increase in prevalence into adulthood?
Rhinitis and conjunctivitis
What is the Allergic march’.
When certain allergies change with change (Either start in childhood and decrease with age or vise versa)
pollen allergies >> whats the allergic match for it
detected initially in young children and then increase with age.
Why is allergy important?
Allergy is common Allergy is associated with significant morbidity Allergy can be fatal
What is food allergy?
how is it classified?
an adverse health effect arising from a specific immune response that occurs on exposure to a food.
Food allergy is classified by immune mechanism into
IgE and non-IgE mediated types.
numerous and frequently reported adverse responses to foods that do not involve the immune response.
Prevalence of each? And lren and sdults
IgE-mediated reactions have been reported to more than 170 foods, so one can be allergic to any food; but food allergies and hence the prevalence estimates are limited to few foods – the commonest being milk, egg and peanuts. The estimated prevalence is higher in children affecting about 6% compared 1-2% of adults.
types of immune mediated and non immine mediated and examples in each
What is scromboid fish toxin?
This is a reaction that results from eating spoiled oily fish (mackerel, tuna) where excess histamine, produced from fish decay, producing symptoms similar to allergy.
examples of Host characteristics that can cause Non-immune mediated
ex: lactose intolerence and physcological or neurological responses ex: food aversion or rohnorea cause by spicy foods
The presenting symptoms of IgE and non-IgE mediated food allergy affect the systems w/ symptoms.
- Symptom onset
- Common foods
- Presenting age
- Natural history
IgE-mediated food allergy can also manifest with behavioural changes describe them
- mood changes (quiet, anxiety),
- agitation and a ‘sense of impending doom’ (described in older children and adults).
Symptoms of non-IgE mediated food allergy can often be ascribed to other conditions as they can be vague Give example
e.g. abdominal pain), not clearly associated with the food contact (i.e. presentation delayed) and can mimic other common gastrointestinal conditions (e.g. colic, gastro-oesophageal reflux in infants).
Food-associated exercise induced anaphylaxis: What is it? Which common foods r effected
Food triggers anaphylaxis only if ingestion is followed temporally (within 2 hours) by exercise (wheat,shellfish, celery).
IgE and non IGE mediated common disorders and symptoms invloved
Different clincial presentations of immediate-onset food allergy
Different clinical presentations of delayed-onset food allergy
Food allergy presentations are influenced by age. Explain this concept
Age: the so-called ‘Food allergic march’. The age at which food allergies present are influenced mainly by individuals’ diet. The natural history of food allergies varies as, as already mentioned, food allergy resolves with increasing age.
Why do food allergy towards foodschange presentations with age?
Child diet becomes diverse and they get older!
What is the commonest food allergy in adults?
Pollen food syndrome
What is Pollen food syndrome ? How do u aquire it? What age does it mainfest?
result of cross-reactivity between the pollens of fruit, vegetables and nuts and pollens causing hay fever e.g. birch.
Heat or stomach acids easily denature these allergens, so symptoms occur only in unprocessed food where that food has had mucosal contact.
On entering the stomach the allergen is denatured preventing absorption and systemic symptoms.
The natural history of foods is either to improve or resolve or to persist.
What r Examples of food allergies that improve? And persist
improve >> milk, egg, wheat and fruit,
persist >> peanut, tree nut, seed, fish and shellfish allergies.
Explain the effects of high temperature and food matrix on food proteins. Give example
cows milk, egg white, eggs, peanut, fish, apple
What is an example of baked milk? When do we use it
Milk in processed biscuits , bc it has lower allergenicity and availability to the immune system so it can be used to re-introduce milk back back in the diet of children w/ milk allergy
Does heating raw milk reduce allergenicity?
Describe the heat and matrix of eggs,what type of egg do we use in resolving egg allergy?
main proteins in eggs, 4 of which are heat labile –
the heat stable and thus immuno- dominant protein ovomucoid comprises about 10% of egg proteins.
A chard boiled egg or well-cooked scrambled egg will therefore have about 80-90% less allergenicity than raw egg (used in mayonnaise).
The allergenicity is further reduced by decreased availability to the immune system in baked egg (e.g. in wheat).
Baked egg is thus used as the initial food in assessing and treating resolving egg allergy.
What things influence the presentation of food allergy.
age, effects of processing and allergen cross-reactivity between related food types.
Describe the implications of cross food allergins
Food families share proteins that can interfere with pt allergic manifestations.
.Make sure when u test for nut allergy for ex: peanut, u check for alll the nuts as an individual presenting with a single nut allergy as the cross-reactivity rate approaches 40%.
Food allergy march
describes different food allergy timing
How does processing affect allergenicity?
By altering proteins
How do we diagnose food allergy? (4 steps)
Patients presenting as an emergency following an acute reaction to foods may have clinical manifestations of:
IgE-mediated food allergy or Non mediated IgE?
How would u take in medical hostory?
What type of physical examination would u take?
Examination must include height and weight in children (and charting on growth chart. Comparison with previous weights to observe trends can also be helpful, particularly to determine whether there are trends of poor weight gain. Examine for concomitant allergic conditions i.e. eczema, allergic rhinitis and asthma.
What screening tests can u do if u siggest igE mediated allergy?
A patient who presents with symptoms suggestive of IgE-mediated food allergy must have the presentation confirmed with the demonstration of IgE sensitisation!
What is skin prick test, why r they useful? how long?
because they provide information within 15 minutes. They are further useful as they can be used to test foods for which there are no blood tests available by pricking the food and then the skin (so-called prick-prick tests).
Results between the two are equivalent.
how can udetect allergen-specific IgE
what screening tests do we do to detect immediate onset symptoms ?
Serum specific IgE – IgE circulating in blood
Skin prick tests – Response of skin mast cells to allergens
Determine presence of sensitivity not allergy
Level of sIgE / size of SPT correlates with likelihood of allergy
• Positive predictive thresholds developed for common allergens
Do not correlate with or predict severity of allergic reaction
Test selection determined by: Clinical history
Targeting likely allergens
Different clincial presentations & symptoms of immediate-onset food(IgE mediated)
& symptoms of delayed onset (non-IgE mediated)