Prevalence of Peanut Allergies

Peanut is one of the eight most common foods to result in food allergic reactions in individuals, with studies demonstrating that peanut allergy (PA) has doubled in the last 10 years (1).  In Australia it is estimated that PA affects 2 – 3% of children by school age, with 80% of these individuals maintaining the allergy for life.  There is a geographical variation for the prevalence of PA, with it being relatively common in Australia, UK, France, Switzerland and USA (1).  In Israel, it is the fourth most common allergen in infants less than two years of age.  Peanut allergy is rarely seen in Italy and Singapore (1). 

Food and Allergens

Peanuts belong to the botanical family, Fabaceae or Leguminosae and are classified as legumes (1).  Other legumes include Beans (soya, runner, French, GoA, haricot, butter, faba, limer); Peas (chickpea, pigeon pea, pea), Lupin, lentils, tamarind, guar, acacia, traganth gum, fenugreek, liquiorice (1).  The cross reactivity between peanut and these other legumes being relatively rare (1).  
Peanut is 26% protein and contains nine known allergens, Ara h 1- 9. Everyone with a peanut allergy will be sensitized to Ara h 2, which is the allergen involved with most reactions, though it is Ara h 1 that is responsible for the most severe reactions (1).  The classification of allergens within superfamilies tends to dictate the cross-reactivity between legumes, seeds, and tree nuts rather than their botanical classification (1).  This cross reactivity between soya protein and other legumes and peanuts is immunological in nature and probably due to the epitopes on the soya protein being homologous to those found within peanut protein (1).  This link does not necessarily translate into clinical cross reactivity (1).  Studies in children have found there is a cross-reactivity of 0.8% – 3% for children having allergies to both peanut and soy bean (1).  This cross-reactivity also exists between peanut and tree nut and is related to the epitope homology rather than the botanical classification (1).  People with peanut allergy are at greater risk (one in five) of having a tree nut allergy (1).

Many allergens are affected by heat treatments and processing, which may alter the allergens potency.  Frying and boiling peanuts has been shown to significantly reduce the amount of Ara h 1 (1).  Roasting peanuts has been found to increase Ara h 1 and Ara h 2 allergens ability to bind to the IgE antibodies 90 fold, resulting in them being more allergenic (1).  In refining peanut oils, virtually all the protein is removed, reducing the oils allergenicity (1). 

Diagnosis of Peanut Allergies

Skin prick test (SPT), along with the measurement of IgE levels in the blood and a detailed clinical history are keys to investigating peanut allergy (1).  In children SPT has been shown to have an excellent negative predictivity and specificity for peanut allergy diagnosis (1). 

Management

The safe and effective management of peanut allergy is the total dietary avoidance of peanuts and all peanut containing foods and drink.  Because of the cross-reactivity of 1 in 5 between peanuts and tree nuts, all tree nuts should also be avoided (1).

At present peanut allergy cannot be treated, with one in five outgrowing this allergy.  Currently underway are clinical trials using immunotherapy, herbal remedies, and epitope alteration (1).  However, the use of desensitization and other treatments presently used in day-to-day clinical practice is a long way off (1).  

Becoming an accomplished food label reader is a key to the management of this allergy. It is important to learn how to read labels as peanut can be listed in various ways peanuts; nuts; ground nuts; earth nuts; monkey nuts; arachis oil; Arachis hypogaea; ground nut oil; peanut oil; peanut flour; peanut butter. 
In accordance with Australian food labelling law, ingredients in foods that may cause severe allergic reactions, such as peanuts, tree nuts (e.g. cashews, almonds, walnuts), shellfish, tinned fish, milk, eggs, sesame and soy beans and their products, must be declared on the label however small the amount (2).  Many food manufacturers use the statement may contain traces, indicating the potential risk of unknown contamination and hence this product should be avoided.  

There is also the possibility that ingredients derived from these foods, may not be clearly identified on the label.  For example soy might be listed as textured vegetable protein? (2).  Fortunately there are a number of food manufacturers who produce their product in nut free environments.  Some of these include Orgran; Hullabaloo; Enjoy Life, and Sweet William. 

Other forms of possible exposure are through human contact and cooking and eating utensils.  Young adults and adolescents are at risk of fatality due to delayed use of adrenalin injection during anaphylaxis (1).  The allergen, Ara h 1 remains in saliva for up to one hour after ingestion (1).  One ml of saliva contains 1110 mg of Ara h 1, indicating the high potential risk of exposure through personal contact and the use of eating utensils.  It is paramount to wash hands and clean cooking utensils and surfaces with soap and water; rather antibacterial washes as these do not remove the allergen (1). 

Table:  Foods which may contain nuts

Food Types Examples
Spreads Peanut Butter, Other Nut Butters
Snacks Peanut Snacks, Trail Mix, Rice Crackers, Chocolate Covered Peanuts, Cereal Bars
Cakes & Biscuits Cookies, Brownies
Ice Creams Nut Toppings
Vegetarian Meals Nut Roast, Veggie Burgers
Sauces Satay Sauce, Salad Dressings (may contain refined peanut oil)
Breakfast Cereals Anything with Crunchy Nut, or Honey Nut, Muesli and other Fruit & Nut Cereals
Meals Out

Indonesian, Malaysian, Thai & Chinese meals often contain peanuts:

Indian Food may also contain peanuts, although other nuts are more likely

by Julie Albrecht Consultant Dietitian-Nutritionist  A.P.D. 
References: 

1.     Tanya Wright and Rosan Meyer., Dietary Management of Milk and Eggs -Food Hypersensitivity: diagnosing and managing food allergies and intolerances ? edited by Isabel Skypala, Carina Venter; Wiley and Blackwell 2009, Part 2, p 117- 128. 
2.    Consumer Information: Information for Allergy Suffers: Food Standards Australia New Zealand, April 2010. www.foodstandards.gov.au

 

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