Parenting / 23 November, 2020 / Dr José Maia e Costa
The (almost) eternal debate on what came first, has persisted through decades. Countless evenings have been spent around a table, with a wine glass (or plenty more), with people throwing arguments against or in favour of one of the answers. Despite all thoughts, in reality the answer is fairly simple. The first animals to lay eggs were the dinosaurs.
A discovery made in 1990 in North America, showed a nest of eggs from a carnivore dinosaur called “Maniraptoran”. This dinosaur is believed to be the animal from which birds came to develop into new species (1, 2). Some suggest the new question: What came first, the dinosaur or the egg? But we will leave that one for another time…
Allergic reactions have been described all the way back to ancient China, Egypt, Greece and Rome, with the Philosopher Lucretius saying, around the first century AD, that “what is food to one man, is bitter poison to others” (3). Despite that, it is hard to say when the first report of an egg allergy was done.
What is probably one of the earliest egg reactions known was an experience made by the French Physiologist François Magendie around 1838. He injected rabbits with egg white and noticed that on second injection they had a reaction which lead to their deaths. Later experiments made in 1902, finally “coined” this reaction as anaphylaxis and identified this could happen not only with egg white but also with milk, toxins, venoms and many animal proteins (4).
It took further four years for Clements von Pirquet to name those reactions as allergies. His remarkable studies on the immune system focused on and lead to further developments on vaccination, hypersensitivity, prophylaxis and anaphylaxis (5). His research, along with more done from other researchers, paved the way to significant developments in immunology.
When it comes to allergies in children, and due to the nature of baby’s weaning, egg sits almost at par with cow’s milk as being the most prevalent form of allergy. This is closely followed by a peanut allergy.
The global incidence of egg allergy varies considerably from country to country, ranging between 0.5% to 2.5% (6). The importance of proper diagnosis of an egg allergy is mainly related to quick action so there is an increase in the chance of outgrowing this allergy.
With proper testing, it is also possible to have a good guess of the severity of the allergy and put a robust management plan in place. This way it is possible to either decrease the risk of an allergic reaction or decrease its severity and side effects when it happens. We also need to consider the use of egg biproducts in the manufacture of medicines and food.
As an example, though the list is not extensive, egg protein is found in:
As you might have guessed by now, not always the same wording will be used to identify the existence of eggs in whatever product you are buying. And this happens despite EU regulations stating the 14 allergens that should be highlighted in foods, though not compulsory for medications (8).
Naturally, the age of first allergic reaction to egg is dependant only on when it is first introduced to a child’s diet! But as with all other foods and their allergies, an initial sensitisation must have occurred in the past. This will mainly through skin contact, being known that children with Atopic Dermatitis (AD) are at higher risk of developing egg allergy (among other allergies).
There are several studies referring to egg sensitisation of egg-eating breastfeeding mothers, also referring to sensitization in Utero (10). On the other hand, some others say the opposite (bearing in mind those are older). Currently, the advice is for pregnant or breastfeeding mothers is NOT to exclude potential allergens in their own diets.
The symptoms seen will depend on whether it is an IgE (immediate type) or non-IgE (delayed type) reaction.
As a potential long term problem to consider, is that children with an egg allergy have an increased risk of developing airborne allergies and asthma, so again the emphasis on early diagnosis and treatment. As a side note, it is common for the development of occupational asthma in bakery workers due to exposure to aerosolized egg.
It is very important to understand that egg associated anaphylaxis rarely lead to fatal outcomes!
Your immediate reaction will be based on what symptoms your child experienced.
It’s very important to understand that when we speak about removing chicken eggs from the diet, we also talk about removing eggs from other birds due to cross-reactivity. The birds’ eggs you should also exclude are turkey, duck, goose, seagull and quail.
Investigations are decided upon the symptoms the child is presenting with. Normally, for a child having immediate type reactions, skin prick tests are the first choice, as their results are highly accurate. Occasionally, when there is a clear history but a negative skin prick test, blood tests can also be done (called specific IgE).
For the delayed kind, a guided exclusion and timely inclusion should be guided by a paediatric dietitian with good knowledge or experience in allergy. Often children will also have OFCs (oral or open food challenges). These challenges are what is called the “gold standard” for diagnosis of a food allergy.
They also guide the paediatric allergist and the paediatric allergy dietitian, on the choice of steps for the reintroduction of egg into a child’s diet.
Up to now it was believed roughly 50% of children would outgrow their egg allergy by 3 years of age, with that percentage increasing to roughly 66% at 5 years of age (6, 10), but it seems those percentages are decreasing with time. The reason for that is unknown still, due to the complicated nature of child development.
It does increase the need for early diagnosis and intervention as we know that the sooner a management is set, the higher will be the chances for children to outgrow their allergy. The initial step is to do an open food challenge to baked egg. If the child passes this step, they will have roughly 95% chance of outgrowing their egg allergy. As you might imagine, failing that challenge will give them less than 5% of outgrowing the allergy.
From that point onward a 5 step egg ladder can be used. The next steps can either be done again in hospital or at home, all depending on the results of further skin prick tests. We cannot forget about the importance of using a wheat-based matrix to increase the chances of passing the first step. That is why the baked egg is normally a fairy cake.
The importance is related to the effect wheat has on the stable protein that exists in egg, called Ovomucoid (OVM) (14). When this protein is mixed with wheat flour, its allergenicity is decreased. This leads to a better tolerance and fewer reactions.
We are not so much concerned about the other proteins in egg, mainly Ovalbumin (OVA) as they are heat degradable. Heat degradable proteins will change their conformation when heated, thus not allowing the protein to connect to the IgE molecule that recognises them, and so not leading to an allergic reaction.
How many times have I been asked if children should avoid chicken if they are allergic to eggs? Not as often as parents telling me their child is allergic to chicken meat or start sneezing when there is either cooked eggs or cooked chicken around. Can this really happen?
Actually, it can, but we need to understand that all are fairly rare. But let us take this into the several aspects that might cause any of the above symptoms.
Chicken meat allergy is considered a primary or genuine food allergy. The origin of this allergy is either related to inhalation of allergens from bird feathers (in adult) or ingestion of egg proteins (in children), though not always being allergic to egg (11, 12, 13). For Bird egg syndrome this is considered a secondary food allergy as often is due to cross-sensitization from proteins either present in egg yolk, chicken meat or bird excrements. It is more common in female adults.
When presenting in children the symptoms are different to adults, mainly the signs are normally respiratory associated (asthma or wheeze) or affects the eyes or nose (rhinoconjunctivitis). In children, it will mainly affect the gastrointestinal tract or leading to breathing problems.
Children with both egg allergy and respiratory symptoms related to bird egg syndrome, tend to either acquire tolerance later or not outgrow it. Normally symptoms start later in their lives (11, 12, 13). The good news is that in both cases what is involved on both of those reactions is a protein present in egg yolk, called Gal d 5. This protein is heat degradable and often children tend to outgrow their egg or chicken meat allergy.
As with egg allergy, be aware of the cross-reactivity between chicken meat and turkey meat. Both need to be excluded. There is another important aspect to focus on – though foods are not airborne, this is not entirely true. If food is being cooked in a stove, the proteins will be aerosolised and can be inhaled. That can lead to an allergic reaction, which can be fairly dangerous, depending on the severity of the child’s own allergy. So if your child has an egg allergy, don’t let him/her be near you when you are cooking eggs!
If you suspect your child has an egg allergy, don’t give up or become demoralised. There is a pretty good chance he/she will outgrow it. Exclude egg and peanut from their diet, exception if already eating peanut.
Ask for a paediatric allergy referral and see if their department will also involve a paediatric allergy dietitian. Don’t try to jump steps, and work closely with the team, as they will help and guide you through this journey. The chances are good that your child will lead a normal life without further worries of allergic reactions (at least to egg).
Consultant Paediatrician in Allergy
Lead Clinician for Paediatric Allergy
University Hospitals Coventry & Warwickshire
PGCert Allergy (Imperial College, London)
PGCert Paed Allergy (Universidade Católica, Lisbon)