Food Allergy

Food allergy is an adverse immune response to food proteins. Most reactions are from peanut, tree nuts, milk, egg, fish, shellfish, wheat, and soya. Symptoms usually appear within 20 minutes of ingestion and nearly always within 2 hours.

Symptoms and signs may vary from pruritus and mild cutaneous eruption to severe anaphylactic respiratory, gastrointestinal, or cardiovascular (e.g., hypotensive) manifestations.

Epinephrine (adrenaline) given by intramuscular injection is the treatment of choice for severe systemic symptoms (anaphylaxis); lesser reactions are managed with a range of therapies from simple withdrawal of suspected food allergen to oral antihistamines.

Food allergy is likely to develop as a result of both genetic and environmental factors. With regard to genetic determinants:

  • Peanut allergy is 7 times more likely to occur in a child with a sibling who is peanut-allergic than in the general population
  • Specific genes contributing to food allergy development have not been identified.

While sensitisation to food proteins is the most common form of allergy to foods of both plant and animal origin, sensitisation to carbohydrate epitopes leading to allergic reaction to mammalian meat has been described. This form of food allergy involves sensitisation to the carbohydrate epitope galactose-alpha-1,3-galactose (alpha-gal). Alpha-gal is a carbohydrate moiety that is present on cells and tissues of all mammals except the higher order primates (including humans). Tick bites can lead to sensitisation of humans to alpha-gal, and subsequent ingestion of meat (e.g., beef, pork, lamb) leads to a delayed allergic reaction. The reaction typically occurs 3 to 6 hours after ingestion. Cross-reactivity with cetuximab has been reported (alpha-gal is present on the Fab portion of the cetuximab heavy chain)

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