Egg allergy is a type of food allergy. It is a hypersensitivity to one or more of the proteins from the yolk or whites of chicken eggs, causing an overreaction of the immune system. The body manifests either an antibody-based immune response or a cell-based immune response to these allergens. Antibody responses are usually rapid and can involve anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Cell-mediated responses take hours to days to appear.
A wide variety of foods can cause allergic reactions, but in the United States 90% of allergic responses to foods are caused by cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans. The Food Allergen Labeling and Consumer Protection Act (FALCPA) of 2004 requires that the label of a food that contains an ingredient that is or contains protein from these eight major food allergens declare the presence of the allergen in the manner described by the law. Lists can be different in different countries. The Japanese Guideline for Food Allergy counts buckwheat and fruit in a top ten list. The European Union requires labeling for the same eight as the United States plus celery, mustard, lupin beans, sesame seeds, sulfites (preservatives for wine) and molluscs.
Egg allergy appears mainly in children, but can persist into adulthood. In the United States it is the second most common food allergy in children after cow's milk. Most children outgrow egg allergy by the age of five, but some people remain allergic for a lifetime. It is usually treated with an exclusion diet and vigilant avoidance of baked foods such as cake or cookies that contain eggs as an ingredient. There is not a scientific consensus as to whether avoidance of developing an allergy may be partly achieved through early introduction of the eggs to the diet of babies at ages 4â€"6 months.
Signs and symptoms
Food allergies usually have a fast onset (from seconds to one hour) and may include: Rash, Hives, Itching of mouth, lips, tongue, throat, eyes, skin, or other areas, Swelling of lips, tongue, eyelids, or the whole face, Difficulty swallowing, Runny or congested nose, Hoarse voice, Wheezing and/or shortness of breath, Diarrhea, Abdominal pain, Lightheadedness, Fainting, Nausea, or Vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated through wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin and fainting. When these symptoms occur the allergic reaction is called anaphylaxis. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show severe symptoms. Untreated, this can proceed to vasodilation, a low blood pressure situation called anaphylactic shock, and death (very rare).
Mechanisms
Most people who are allergic to hen's eggs have antibodies which react to one of four proteins in the egg white: ovomucoid, ovalbumin, ovotransferrin, and lysozyme; ovomucoid, also called Gal d 1, is the most common target of immune system attack. The egg yolk contains several potential antigens: livetin, apovitillin, and phosvitin.
A person who reacts only to a protein in the egg yolk may be able to easily tolerate egg whites, and vice versa, although it is difficult to separate yolks so that there is no egg white attached. Some people will be allergic to proteins in both the egg white and the egg yolk. Egg yolk allergies may be somewhat more common in adults. A small number of people who are allergic to eggs will develop an allergy to chicken or other poultry meats.
Eggs and exercise combined
There is a condition called food dependent, exercise-induced anaphylaxis (FDEIAn). Exercise can trigger anaphylactic symptoms. For some people with this condition, exercise alone is not sufficient, nor consumption of a food to which they are mildly allergic to be sufficient, but the two in combination can trigger anaphylaxis. A review mentions case studies of this being true for eggs.
Non-allergic egg white intolerance
Egg whites, which are potentially histamine liberators, also provoke a nonallergic response in some people. In this situation, proteins in egg white directly trigger the release of histamine from mast cells on contact. Because this mechanism is classified as a pharmacological reaction, or "pseudoallergy", the condition is considered a food intolerance instead of a true immunoglobulin E (IgE) based allergic reaction.
The response is usually localized, typically in the gastrointestinal tract. Symptoms may include abdominal pain, diarrhea, or any symptoms of histamine release. If sufficiently strong, it can result in an anaphylactoid reaction, which is clinically indistinguishable from true anaphylaxis. Some people with this condition tolerate small quantities of egg whites. They are more often able to tolerate well-cooked eggs, such as found in cake or dried egg-based pasta, than incompletely cooked eggs, such as fried eggs or meringues, or uncooked eggs.
Diagnosis
Diagnosis of egg allergy is based on the person's history of allergic reactions, skin prick test (SPT), patch test and measurement of egg-specific serum immunoglobulin E (IgE or sIgE). Confirmation by double-blind, placebo-controlled food challenges. SPT and sIgE have sensitivity greater than 90% but specificity in the 50-60% range, meaning these tests will detect an egg sensitivity, but will also be positive for other allergens. For young children, attempts have been made to identify SPT and sIgE responses strong enough to avoid the need for a confirming oral food challenge.
Prevention and treatment
When eggs are introduced to an infant's diet is thought to affect risk of developing allergy, but there are contradictory recommendations and guidelines. A 2016 review acknowledged that introducing peanuts early appears to have a benefit, but stated "The effect of early introduction of egg on egg allergy are controversial." A meta-analysis published the same year supported the theory that early introduction of eggs into an infant's diet lowers risk, and a review of allergens in general stated that introducing solid foods at 4â€"6 months may result in the lowest subsequent allergy risk. However, an older consensus document from the American College of Allergy, Asthma and Immunology recommended that introduction of chicken eggs be delayed to 24 months of age.
Prevention of egg-allergic reactions means avoiding eggs and egg-containing foods. People with an allergy to chicken eggs may also be allergic to other types of eggs, such as goose, duck or turkey eggs. Food companies produce egg substitutes, egg-free mayonnaise and other replacement food that are free of egg proteins. People with severe allergic reactions to eggs, such as anaphylaxis are advised to carry injectable epinephrine for use in emergency.
There is active research on trying oral immunotherapy (OIT) to desensitize people to egg allergens. A Cochrane Review of four clinical trials concluded that OIT can desensitize people, but it remains unclear whether long-term tolerance develops after treatment ceases, and 69% of the people enrolled in the trials had adverse effects. The authors concluded there was a need for standardized protocols and guidelines prior to incorporating OIT into clinical practice. A second review noted that allergic reactions, up to anaphylaxis, can occur during OIT, and recommends this treatment not be routine medical practice. A third review limited its scope to trials of baked egg-containing goods such as bread or cake as a means of resolving egg allergy. Again, there were some successes, but also some severe allergic reactions, and the authors came down on the side of not recommending this as treatment.
Cooking without eggs
In cooking, eggs are multifunctional: they may act as an emulsifier to reduce oil/water separation (mayonnaise), a binder (water binding and particle adhesion, as in meatloaf), or an aerator (cakes, especially angel food). Some commercial egg replacers can substitute for particular functions (potato starch and tapioca for water binding, whey protein for aeration or particle binding, or soy lecithin or avocados for emulsification). Alfred Bird invented egg-free Bird's Custard, the original version of what is known generically as custard powder today.
Most people find it necessary to strictly avoid any item containing eggs, including:
Ingredients that sometimes include egg protein include: artificial flavoring, natural flavoring, lecithin and nougat.
Probiotic products have been tested, and some found to contain milk and egg proteins which were not always indicated on the labels.
Epidemiology (prevalence)
In countries in North America and western Europe, where use of cow's milk based infant formula is common, chicken egg allergy is the second most common food allergy in infants and young children after cow's milk. However, in Japan, egg allergy is first and cow's milk second, followed by wheat and then the other common allergenic foods. A review from South Africa reported egg and peanut as the two most common allergenic foods
Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time. Egg allergies are usually observed in infants and young children, and often disappear with age (see Prognosis), so prevalence of egg allergy may be expressed as a percentage of children under a set age. One review estimates that in North American and western European populations the prevalence of egg allergy in children under the age of five years is 1.8-2.0%. A second described the range in young children as 0.5-2.5%. Although the majority of children develop tolerance as they age into school age years, for roughly one-third the allergy persists into adulthood. Strong predictors for adult-persistent allergy are anaphylactic symptoms as a child, high egg-specific serum IgE, robust response to the skin prick test and absence of tolerance to egg-containing baked foods. Self-reported allergy prevalence is always higher than food-challenge confirmed allergy. For all age groups, a review of fifty studies estimated 2.5% for self-reported egg allergy and 0.2% for confirmed. Adult-onset of egg allergy is rare, but there is confirmation of cases. Some were described as having started in late teenage years; another group were workers in the baking industry who were exposed to powdered egg dust.
Video Egg allergy
Prognosis
The majority of children outgrow egg allergy. One review reported that 70% of children will outgrow this allergy by 16 years, and children will be able to tolerate eggs as an ingredient in baked goods and well-cooked eggs sooner than under-cooked eggs. In subsequently published longitudinal studies, one reported that for 140 infants who had challenge-confirmed egg allergy, 44% had resolved by two years. A second reported that for 203 infants with confirmed IgE-mediated egg allergy, 45% resolved by two years of age, 66% by four years, and 71% by six years. Resolution more likely if baseline serum IgE was lower, and if the baseline symptoms did not include anaphylaxis.
Maps Egg allergy
Vaccine hazards
Influenza vaccines are created by injecting live virus into fertilized chicken eggs. The viruses are harvested, killed and purified, but a residual amount of egg white protein remains. Each year, vaccines are created to provide protection against the flu viruses expected to be prevalent in the upcoming cold weather months. For the 2017-2018 flu season the vaccines are described as IIV3 and IIV4 for resistance to the expected three or four viruses. For adults ages 18 and older there is also an option to receive recombinant flu vaccines (RIV3 or RIV4) which are grown on mammalian cell cultures instead of in eggs, and so are no risk for people with severe egg allergy. Recommendations are that for people with a history of mild egg allergy should receive any IIV or RIV vaccine. People with a more severe allergic reaction may also receive any IIV or RIV, but in an inpatient or outpatient medical setting, administered by a healthcare provider. People with a known severe allergic reaction to influenza vaccine (which could be to egg protein or the gelatin or the neomycin components of the vaccine) should not receive a flu vaccine.
Each year the American Academy of Pediatrics (AAP) publishes recommendations for prevention and control of influenza in children. In the most recent guidelines, for 2016-2017, a change was made, that children with history of egg allergy may receive the IIV3 or IIV4 vaccine without special precautions. It does however state that "Standard vaccination practice should include the ability to respond to acute hypersensitivity reactions." Prior to this, AAP recommended precautions based on egg allergy history: if no history, immunize; if history of mild reaction, i.e., hives, immunize in a medical setting with healthcare professionals and resuscitative equipment available; if history of severe reactions, refer to an allergist.
The measles and mumps parts of the "MMR vaccine" (for measles, mumps and rubella) are cultured on chick embryo cell culture, and contains trace amounts of egg protein. The amount of egg protein is lower than in influenza vaccines and the risk of an allergic reaction is much lower. One guideline stated that all infants and children should get the two MMR vaccinations, mentioning that "Studies on large numbers of egg-allergic children show there is no increased risk of severe allergic reactions to the vaccines." Another guideline recommended that if a child has a known medical history of severe anaphylaxis reaction to eggs, then the vaccination should be done in a hospital center, and the child be kept for observation for 60 minutes before being allowed to leave. The second guideline also stated that if there was a severe reaction to the first vaccination - which could have been to egg protein or the gelatin and neomycin components of the vaccine - the second is contraindicated.
Society and culture
Children with allergies experience a decreased quality of life compared to their age-peers. In school and social situations they report an increased occurrence of bullying because of their allergy, which may include being touched with foods they are allergic to or having their snacks and meals intentionally contaminated with the food they need to avoid.
See also
- Food allergy (has images of hives, skin prick test and patch test)
- List of allergens (food and non-food)
References
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