Food Allergy in children

What are adverse reactions to foods?

It is an untoward reaction provoked by ingesting food or food additives. There are 2 types of adverse food reactions:

1. Physiologic: This is due to food intolerance. E.g., Lactose intolerance
2. Pathologic/Immune-Mediated: This is due to Food allergy

Classification of adverse reactions to food

A. Food Intolerance (non-immune)

1. Related to host factors

• Enzyme deficiency: lactase deficiency, sucrase/isomaltase deficiency, hereditary fructose intolerance, galactosemia.
• GIT disorders - IBD (inflammatory bowel disease), IBS (irritable bowel syndrome), and pseudo-obstruction.
• Idiosyncratic reactions: caffeinated beverages lead to hyperactivity.
• Psychological - Food phobias, OCD (obsessive compulsive disorders).
• Migraine

2. Related to food factors

• Infectious organisms: E. coli, staph aureus, Cl. perfringens, Shigella, Salmonella, Botulism, Yersinia, Campylobacter.
• Toxins—histamine (scombroid poisoning), saxitoxin (shellfish poisoning).
• Drugs: caffeine, Tyramine(cheese), theobromine (chocolate, tea), tryptamine (tomato), and benzoic acid in citrus fruits (perioral flare).
• Contaminants—heavy metals, antibiotics, and pesticides.

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B. Food Allergy

1. IgE Mediated

2. Mixed: Non-IgE and IgE mediated

3. Non-IgE mediated (mediated by T-lymphocyte)

Epidemiology

Worldwide estimates of food allergy prevalence are 1-10%. Up to 6% of children experience food allergy in the 1st 3 years of their life. Cow's Milk Allergy: 2.5%, Peanut Allergy: 2-3%, Egg allergy: 2%. Most children outgrow milk and egg allergies by approx. 50% by school age. In contrast, 80-90% of children with peanut or seafood allergies retain their allergy for life.

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Genetic factors in food allergy

• Positive family history is at 2 to 10 times higher risk.
• Association with HLA-DQ variants. Especially in Differential methylation at the HLA-DR and DQ regions
• Genes implicated
  • Filaggrin: responsible for atopic dermatitis and food allergies in children.
  • Interleukin 10
  • STAT6
  • FOXP3
• DNA methylation effects on interleukins 4,5 and 10 and IFN-g genes in the MAP-kinase pathway have been implicated.

Pathogenesis of food allergies

Different for IgE-mediated and non-IgE-mediated.

• In IgE-mediated process
  • In the first few years of life, exposure to certain allergens occurs.
  • This leads to the production of IgE. which, in turn, gets attached to the surface of mast cells and basophils by the FCE receptor.
  • The above whole process is known as priming or sensitization.
  • Whenever an allergen comes in contact, there is a rapid release of mediators from mast cells.
  • Mediators directly cause systemic effects and will also recruit inflammatory cells like basophils, eosinophils, macrophages to the site and produce food allergy
• In the Non-IgE mediated process
  • Non-IgE mediation occurs by cell-mediated response, which releases T lymphocytes yet the undefined role of innate immune disorders also contributes.

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Types of food allergens in IgE-mediated food allergies

Class 1: Penetrating GIT Barrier

This may serve as a class 1 food allergen, but eggs, milk, peanuts, tree nuts, fish, soy, and wheat account for 90%. Cell-mediated sensitivity develops - only to class 1 IgE-mediated food allergy.

Class 2: Those that are partially homologous to plant pollen's respiratory tract

These are typically vegetable, fruit, or nut proteins partially homologous to pollen proteins. Cell-mediated immunity does not develop.

Clinical Manifestations

GIT Manifestations

Often the 1st form of food allergy in infants and young children. Cell-mediated mechanisms are more common than IgE based. Manifest as vomiting, irritability, diarrhea, and Failure to thrive. Broadly classified into 2 categories

Food protein-induced GIT symptoms

FPIES - Food Protein-Induced Enterocolitis Syndrome

• In the 1st few months, develops symptoms such as vomiting, irritability, diarrhea, and abdominal distention.
• Allergic to cow's milk protein, soy-based formula.
• 15% of children tend to develop hypotension; most of them improve by 3-5 years of age.

FPIAP - Food Protein-Induced Allergic Proctocolitis

• · In the 1st few months, symptoms such as diarrhea, vomiting, and abdominal distention develop. Allergic to 60% breast milk and 40% cow's milk/soy milk.

FPE - Food Protein-Induced Enteropathy

• Most common cases develop cow's milk protein allergy.
• Most severe cases develop celiac disease.

Eosinophilic Gastro Enteropathy

• Eosinophilic esophagitis
• Eosinophilic gastroenteritis

IGE-Mediated GIT symptoms

1. Oral Allergy Syndrome

Can be associated with pollen-induced allergic rhinitis. Oral pruritus; tingling and angioedema of the lips, tongue, palate, and throat; pruritus in the ears; and tightness in the throat. Short-lived symptoms precipitated by raw fruits and vegetables.

2. Acute GIT Allergy

Acute abdominal pain, vomiting, or diarrhea when IgE-mediated allergic symptoms develop in other target organs.

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Skin Manifestation 

It is common in infants and young children. It is associated with atopic dermatitis. At least 30% of children with moderate to severe AD have food allergies. The most common symptoms are acute urticaria and angioedema. Most are IgE-mediated. Foods most implicated include eggs, milk, and peanuts.

Other Systemic Manifestations

• Respiratory: Food-induced rhinoconjunctivitis symptoms typically accompany allergic symptoms in other target organs, such as skin. Isolated respiratory involvement in food allergies is very rare.
• Wheezing occurs in approximately 25% of IgE-mediated food allergic reactions.
• Anaphylaxis: Anaphylaxis is defined as a serious, multisystem allergic reaction that is rapid in onset and potentially fatal.

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