Prevalence of Tree Nut Allergies
There is a geographical variation in the prevalence of tree nuts which relates the type of nuts consumed in that country. In Australia cashew nut allergy is the most common in infants affecting 0.33% and hazelnut 0.18% and walnut 0.16%, with allergies to Brazil are almond being rarely seen (1).    In the USA tree nut allergy has been reported to be increasing with walnut, almond and pecan being the most common (1).  In the UK the most common tree nut allergies are to Brazil, almond and hazelnut (1).   Cashew nut allergy appears to display a similar clinical history to peanut allergy including wheezing and even anaphylaxis (1).  Oral Allergy Syndrome (OAS) is also seen with hazelnuts, hence the importance of the true diagnosis of nut allergy (1).  With tree nut allergy, it is estimated that only 9% of allergies are outgrown with cashew nut allergy rarely being outgrown (1). 
Foods and Allergens
Tree nuts include cashew, almond, Brazil, hazelnut, chestnut, pistachio, pecan, walnut, macadamia nut, pinenut and coconut (1).  As with legumes it is the plant food superfamily classification of the allergens in tree nut allergy which are of importance (1).  
Studies have shown a strong clinical cross reactivity between tree nuts and peanuts within allergic individuals. In the general population the risk of having both is 2.5 %.  The risk is considerably higher in atopic individuals and studies have estimated this to be 23 ? 50 %. 
Oral Allergy Syndrome can also be triggered by tree nuts, with the most common cross reactivity occurrs between allergens from almonds, hazelnuts, and walnuts and the antibodies to the main birch pollen allergens (1).  A similar cross reactivity can also occur between latex and some tree nuts (1). 
Diagnosis of Tree Nut Allergy
Skin prick tests and specific Ig E tests in conjunction with a good clinical history are keys to the diagnosis of tree nut allergy. When these results are contradictory then a medically supervised  oral food challenge is required for diagnosis (1).  
Management
At present the only effective and proven management of any tree nut allergy is the total avoidance of the offending allergen (1). 

Table: alternative name for nuts and foods likely to contain nuts

Nut Alternative Names 
Hazelnut Filbert, cob nut
Macadamia Queensland nut, candle nut
Pecan Hickory Nut
Spreads Chocolate Hazelnut Spread
Snacks & Sweets Cereal bars, mixed nuts, praline, nougat, Turkish Delight, marzipan
Cakes & Biscuits Cookies, brownies, fruit cake, anything with marzipan, almon croissants
Ice Creams Nut toppings, pistachio ice cream, kulfi
Vegetarian Meals Nut Roast, Veggie Burgers
Sauces Almond essence, nut oils
   
   

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

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

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