INTRODUCTION
Food allergy is recognized as a common worldwide problem, and, like other atopic disorders, its incidence seems to increase. In the past years, investigations of allergic food proteins and related immunological responses have moved to the molecular level, and the newly-found knowledge might provide novel experimental strategies for the laboratory diagnosis and the immuno-modulatory control of food-induced allergic reactions .
Approximately 20% of the population alters their diet for a perceived adverse reaction to food, but the application of double-blind placebo-controlled oral food challenge, the "gold standard" for diagnosis of food allergy, shows that questionnaire-based studies overestimate the prevalence of food allergies. The clinical disorders determined by adverse reactions to food can be classified on the basis of immunologic or no immunologic mechanisms and the organ system or systems affected.
The true prevalence of food allergy is lower and seems to range from 1% to 4% of the general population and about 6% of the general population and about 6% of the pediatric population, but does occur in as much as 25% of children with eczema6. Allergic hypersensitivity simply put, is an adverse immune reaction to a protein (or allergen) in our environment, which is normally harmless to the non-allergic person. It may present as mild itching of the skin, tissue swelling and wheezing or even progress to full-blown anaphylaxis and death. 18 million allergy sufferers live in the UK where 4% of the populations also have a food allergy.
Allergy develops after repeated exposure to the causative allergen. Sensitization takes place on initial exposure (a process that may take up to six weeks to develop) and no adverse reaction appears to occur during initial sensitization.
(A) DEFINITION
A food allergy is an immunologic response to a food protein and caused by allergens in the food that are a kind of protein in the food. These proteins resist the cooking process, the acid in the stomach and the enzymes in the stomach and intestines and enter the blood stream and they cause the allergy reaction after they enter the blood stream.
(B) SIGNS AND SYMPTOMS
Symptoms of food allergies are: -
1. Anaphylaxis: - a severe, whole-body allergic reaction that can result in death. Leads to vasodilation and, if severe, symptoms of life-threatening shock.
2. Angioedema: - rapid swelling (edema) of the skin, mucosa and submucosal tissues, especially of the eyelids, face, lips, and tongue.
3. Eczema is a form of dermatitis, or inflammation of the upper layers of the skin.
(a). Atopic eczema (aka infantile e., flexural e., atopic dermatitis) is believed to have a hereditary component, and often runs in families whose members also have hay fever and asthma. Itchy rash is particularly noticeable on face and scalp, neck, inside of elbows, behind knees, and buttocks.
(b). Contact dermatitis is of two types: allergic (resulting from a delayed reaction to some allergen, such as poison ivy or nickel), and irritant (resulting from direct reaction to a solvent, for example). Some substances act both as allergen and irritant (e.g. wet cement). Other substances cause a problem after sunlight exposure, bringing on phototoxic dermatitis.
(c). Xerotic eczema (aka asteatotic e., e. craquele or craquelatum, winter itch,
pruritus hiemalis) is dry skin that becomes so serious it turns into eczema. It worsens in dry winter weather, and limbs and trunk are most often affected. The itchy, tender skin resembles a dry, cracked, river bed. This disorder is very common among the older population.
(d). Seborrhoeic dermatitis (aka cradle cap in infants, dandruff) causes dry or greasy scaling of the scalp and eyebrows. Scaly pimples and red patches sometimes appear in various adjacent places. In newborns it causes a thick, yellow crusty scalp rash called cradle cap which seems related to lack of biotin, and is often curable.
4. Skin rashes, such as nettle rash (also called urticaria or hives). Some of these longer lasting rashes are called atopic dermatitis.
5. Itching of the mouth, throat, eyes, skin, or any area
6. Nausea, vomiting, diarrhoea, stomach cramps, or abdominal pain
7. Running nose or nasal congestion
8. Wheezing, scratchy throat, shortness of breath, or difficulty swallowing
9. Mood swings, depression: The symptoms of an Immunoglobulin E (IgE) allergic reaction can take place within a few minutes to an hour. The process of eating and digesting food affects the timing and location of a reaction. IgG reactions build over a period of hours to days, and therefore symptoms can be difficult to notice as allergy-related.
TYPES OF ALLERGENIC FOOD
There are a number of groups of foods that are responsible for causing the majority of food allergies. Rice allergy is more common in East Asia where rice forms a large part of the diet. In Central Europe, celery allergy is more common. The top allergens vary somewhat from country to country but milk, eggs, peanuts, tree nuts, fish, shellfish, soy, wheat and sesame tend to be in the top ten in many countries.
The most common food allergies are: -
1. Milk allergy:-
Two out of a hundred infants under one year old suffer from cow's milk allergy, making it the most common food allergy of childhood. In general children lose this sensitivity as they grow up with nine out of ten losing it by the age of three; it is unusual for adults to suffer from this allergy. Symptoms are frequently vomiting and diarrhoea in children, with 30-50% also having skin rashes of some type. A small number of children have an anaphylactic reaction to milk which tends to be life-long.
The major allergens in milk are the caseins and the protein b-lactoglobulin. People are usually allergic to more than one kind of milk protein. The proteins from cow's milk are very similar to those from goats and sheep. Thus goat's or sheep's milk cannot be used as a cow's milk substitute in allergic individuals.
A report about 22-year-old Female patient is described who was repeatedly hospitalized on account of severe asthmatic attacks presumably due to the ingestion of cow's milk or milk-containing products. There were no signs of gastrointestinal disturbance, but some urticaria and angioedema occurred. Strongly positive RASTs (radioallergosorbent test) were observed in the blood serum against the proteins in cow's milk, bovine serum, egg white, cod fish, and house dust. The symptoms were successfully controlled by rigorous dietary measures.
2. Eggs:-
Allergy to eggs is usually observed in young children rather than adults, and like cow's milk allergy, fades with time. Occasionally children suffer from a severe form of allergy which is not outgrown.
The main allergens are the egg white proteins ovomucoid, ovalbumin, and ovotransferrin. The eggs of other poultry, such as ducks, are very similar to those of hens and can cause reactions in egg-allergic individuals.
3. Peanut allergy:-
Peanuts are one of most allergenic foods and frequently cause very severe reactions, including anaphylaxis. Allergy to peanuts is established in childhood and usually maintained throughout life. Peanut allergy can be so severe that only very tiny amounts of peanut can cause a reaction. Thus the traces of nuts found in processed oils, or the carryover of materials on utensils used for serving foods, can be enough in some individuals, to cause a reaction. The main allergens in peanuts and Soya are the proteins used by the seed as a food store for it to grow into a seedling. One of the allergens in Soya bean is very similar to a major allergen from dust mites, a common environmental allergen. We aren't sure yet whether this means there is a link between dust allergy and Soya allergy.
A large number of children who develop peanut allergy have their first reaction the first time they are given a peanut-containing product (usually a dab of peanut butter). A large number of children who develop peanut allergy have their first reaction the first time they are given a peanut-containing product (usually a dab of peanut butter). Peanut protein could pass into breast milk Twenty-three lactating women; aged 21 to 35 years ate 50 grams of dry roasted peanuts (about 60 peanuts or 1/3 cup). Breast milk samples were collected at hourly intervals. Peanut protein was found in the breast milk of 11 of the mothers. In 10 mothers, it was detected within two hours after she ate peanuts, in one mother it was detected six hours later.
That peanut protein is secreted into breast milk, thus sensitizing the baby who is at risk for developing an allergy. This may explain why up to 85 percent of children have a peanut allergy reaction the first time they eat a peanut-containing product. A baby born into a family with allergies.
[Note: - Milk, eggs, and wheat have previously been shown to pass into breast milk. The mothers from allergic families eliminate peanuts and tree nuts (e.g., almonds, walnuts, etc.) and consider eliminating eggs, milk, fish, and perhaps other foods from their diets while nursing. If you choose to do this, be sure to speak with a registered dietitian to be sure your diet is well-balanced .
4. Tree Nut Allergy:-
This group includes true tree nuts, such as Brazil nuts, hazelnuts, walnut and pecan. Whilst not as intensively studied as peanuts, indications are that tree nuts can cause symptoms as severe which can occasionally be fatal. Children who become sensitized to tree nuts tend to remain allergic throughout life. Hazelnut and almond allergies are more like those people get to fruit, and are linked to pollen allergies. Nut allergens can be both destroyed by, and resistant, to cooking and we think that roasting may actually create new allergens. The allergens can be the seed storage proteins, or other molecules which are also found in pollen.
5. Fish and shellfish allergy:-
Allergies to shellfish are unusual in children, mostly being experienced by adults. Reactions to fish are found in children and adults. The incidence of seafood allergy is higher in those countries with a high consumption of fish and shellfish. Severe reactions are more frequently found with these foods, including anaphylaxis. Cooking does not destroy the allergens in fish and shellfish, and some individuals maybe allergic to the cooked, but not raw, fish. The major allergens in fish are flesh proteins called parvalbumins which are very similar in all kinds of fish. Shellfish allergens are usually found in the flesh and are part of the muscle protein system, whilst in foods such as shrimps, allergens have also been found in the shells.
If pregnant or trying to be, avoid seafood and shellfish. Some believe that it may cause your child to develop food allergy.
6. Fruits allergy:-
In general allergic reactions to fruits and vegetables are mild, and are often limited to the mouth, and are called the oral-allergy syndrome (OAS). Around four out of ten people having OAS are also allergic to tree and weed pollens. Thus people who are allergic to birch pollen are much more likely to be allergic to apples. There allergens in fruits and vegetables are not as complicated as other foods. Many of them are very like the allergens in pollens, which is why people with pollen allergies are also allergic to certain fruits.
Many fruit allergens are destroyed by cooking, and thus cooked fruits are often safe for fruit allergic people to eat. Allergies to latex gloves, especially amongst health professionals, are increasing. As many of the latex allergens are like those found in certain tropical fruits, such as bananas, these people can get an allergic reaction to handling or eating these foods. Tomato Allergy: - Reported on four cases (two adults with throat constriction, one child with gastro esophageal reflux disease [GERD], one child with atopic dermatitis) with IgE-mediated reactions to tomatoes.
Using extracts prepared from the skin, seeds, and fleshy fruit of the tomato, specific IgE antibody in the sera of patients was detected by ELISA. After characterizing the extracts for their antigen profile and reactivity with IgE, proteins were separated by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). Of the four patients, one adult showed higher IgE against tomato skin extract. Western blot tests of the patient's scrum with tomato skin extract also revealed reaction with a protein band in the 42-45kD region. Tomato allergy can be manifested as atopic dermatitis, laryngeal angioedema, and even gastroesophageal reflux.
7. Cereals allergy:
Suffered by children and adults alike, wheat allergy appears to be particularly associated with exercise-induced anaphylaxis. The more of a cereal (wheat, rye, barley, oats, maize or rice) we eat the more likely we are to suffer an allergy. Thus rice allergy is found more frequently in populations eating ethnic diets. Seed storage proteins (such as wheat gluten) and other proteins present in grain to protect it from attack by moulds and bacteria, have been found to be major allergens.
8. Penicillin's allergy reaction:
Frequently manifestations are – rash, itching, urticaria and fever. Wheezing, angioneuritis, edema, serum sickness and exofolliative dermatitis are less common. Anaphylaxis is rare but may be fatal. Fear of anaphylactic shock has several restricted the use of injPnG in general practice. All form of penicillin (natural or semi synthetic) can cause allergy but it is more commonly seen after parenteral administration.
Penicillin produce hypersensitivity – urticaria, angioedema, bronchiospasm, anaphylaxis or serum sickness. If earlier reaction had been only a rash, penicillin may be given cautiously – often no untoward effect is seen. History of penicillin allergy must be elicited before injection it. A scratch test on intradermal test (with 2 – 10 u ) may be performed first. On occasion, his it has caused fatal anaphylaxis. Testing with benzyl-penicilloyl – polylysine is safer. However a negative intradermal test does not rule out delayed hypersensitivity. It should also be released that presence of antibodies to penicillin does not mean allergy to it, because practically everyone who receives penicillin develop antibodies to it.
For the development of antibodies, penicillin or a product of it (mostly penicilloyl moiety – major determent) act as a hapten. Topical use of penicillin is highly sensitizing (contact dermatitis and other reaction). Therefore, all topical preparation of penicillin (including eye ointment) have been banned, except for use in eye as solution in case of
gonococcal opthalmia.
