Elsevier

The Lancet

Volume 371, Issue 9623, 3–9 May 2008, Pages 1538-1546
The Lancet

Seminar
Peanut allergy

https://doi.org/10.1016/S0140-6736(08)60659-5Get rights and content

Summary

Peanut allergy has become a major health concern worldwide, especially in developed countries. However, the reasons for this increasing prevalence over the past several decades are not well understood. Because of the potentially severe health consequences of peanut allergy, those suspected of having had an allergic reaction to peanuts deserve a thorough evaluation. All patients with peanut allergy should be given an emergency management plan, as well as epinephrine and antihistamines to have on hand at all times. Patients and families should be taught to recognise early allergic reactions to peanuts and how to implement appropriate peanut-avoidance strategies. It is imperative that severe, or potentially severe, reactions be treated promptly with intramuscular epinephrine and oral antihistamines. Patients who have had such a reaction should be kept under observation in a hospital emergency department or equivalent for up to 4 h because of the possible development of the late-phase allergic response. This Seminar looks at the changing epidemiology of this allergy—and theories as to the rise in prevalence, diagnosis, and management of the allergy, and potential new treatments and prevention strategies under development.

Introduction

Peanut allergy is an IgE-mediated disease that affects approximately 1% of children under the age of 5 years.1, 2, 3 In the past 15 years, increasing numbers of children have been diagnosed with the allergy.4, 5 Food allergy in general affects 6–8% of children younger than 4 years, and about 4% of the US population older than 10 years.6, 7 While any food can potentially cause an allergic reaction, a few cause most allergic reactions. In both children and adults, peanuts, tree nuts, fish, and shellfish are common allergens.1, 3 Children also often react to milk, eggs, wheat, and soy.1, 3

Food allergy is the leading cause of anaphylaxis treated in hospital emergency departments in Western Europe and the USA. In the USA, food allergy alone accounts for about 30 000 anaphylactic reactions, 2000 hospital admissions, and 200 deaths each year.8 The treatment strategy for most allergic diseases is based on avoidance of the allergen, pharmacological therapy, and if needed, allergen-specific immunotherapy. For peanut allergy, immunotherapy is not yet available.

Section snippets

Epidemiology

The rise in peanut allergy has been well documented in a population-based study of 3-year olds in the UK, in which the prevalence of sensitisation to peanuts rose from 1·3% to 3·2% between 1989 and 1995.5 National surveys in the USA suggest that 1·1% of Americans—3 million people—are allergic to peanuts, tree nuts, or both.7, 9 Similarly, data from a US National Health and Nutritional Examination Survey (1988–94) indicated that 8·6% of Americans have skin-prick test evidence of sensitivity to

Pathophysiology

The initial introduction of a food allergen generally occurs at the mucosal surface of the gastrointestinal tract.17 Food proteins are taken up by specialised epithelial cells, M cells, transferred to antigen-presenting cells such as dendritic cells, and processed into peptide fragments presented on the cell surface by class II MHC molecules (figure).18, 19 Peptides are then presented to naive T helper (Th) cells via MHC/T cell receptor interaction, resulting in Th cell priming and activation.

Diagnosis

Peanut allergy is a typical IgE-mediated immune disease. Clinical symptoms develop within seconds, and up to 2 h after ingestion of even a few milligrams of peanut protein (one peanut has about 300 mg of protein). In general, the peanut must be eaten before life-threatening symptoms will occur—ie, the allergy is not often triggered by skin or air contact with the peanut protein. The mean age of diagnosis in children is 14 months, with symptoms occurring after the first known peanut ingestion in

Allergy management

The current treatment (panel 1) of peanut allergy consists of educating patients and their families about how to avoid the accidental ingestion of peanuts, and the recognition and the management of the early stages of an IgE-mediated reaction (panel 2).4 Children are often advised to avoid tree nuts if they are allergic to peanuts because of safety concerns for cross-contamination and allergen cross-reactivity. Peanuts are legumes, a plant family that includes soybeans, green beans, and

Changes in epidemiology

The rise in prevalence of peanut allergy has prompted a search for explanations of this change in epidemiology. In addition to theories about the increase in allergic disease in general (eg, the hygiene hypothesis, which says that not enough exposure to infectious agents in early childhood can increase susceptibility to allergic disease), several factors have been suggested to account for the change in peanut allergy. Allergic reactions require previous immune sensitisation since IgE antibodies

New developments

One approach that may decrease the overall prevalence of peanut allergy is to develop transgenic plants that produce hypoallergenic peanuts.80 An example would be to introduce antisense RNA copies of the allergen gene into the peanut plant to suppress allergen gene expression. Post-translational gene silencing by mRNA degradation is another approach being investigated.76 This technique introduces an exogenous truncated copy of an endogenous allergen gene into a plant, leading to degradation of

Future treatments

In view of the severity of the clinical reactions from peanut allergy and because the allergy can be life-long, effective treatments need to be developed.83 Traditional subcutaneous allergen immunotherapy with crude peanut extract has not been feasible for peanut allergy because of the high risk of severe systemic side-effects of the therapy, including life-threatening anaphylaxis.84, 85

Novel immunotherapeutic strategies designed to alter the immune system's response to food allergens are

Search strategy and selection criteria

We searched Medline for publications from 1975 to 2006 and the Cochrane Library for reports from 1990 to 2006. We used the search terms “peanut allergy”, “peanut”, “food allergy”, “anaphylaxis”, “food anaphylaxis”, “peanut allergens”, “allergy immunotherapy”, and “food immunotherapy”. We translated all non-English language publications that resulted from this search strategy. We largely selected publications from the past 5 years, but did not exclude commonly referenced and highly

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