Cross-Reactivity to Mahaleb Spice in a Subject with Allergies to Almond and Other Tree Nuts

Introduction: In 2014 and 2015, a number of food recalls occurred worldwide due to contamination of ground spices with peanut and tree nut residues. A subset of these recalls associated with putative almond contamination in cumin were later rescinded in Canada and the UK when confirmation testing attributed the contamination to mahaleb residues. Routine immunodiagnostic-based and PCR-based methods for almond determination were unable to discriminate between almond residues and closely related mahaleb proteins. Liquid chromatography-tandem mass spectrometry and PCR-based techniques were later employed by the UK FOOD Standards Agency and the Canadian Food Inspection Agency to identify mahaleb-specific markers in these cumin samples.

Purpose: In view of the inability of routine testing to distinguish between almond and mahaleb, it is important to know whether mahaleb proteins present a risk for almond-allergic consumers. To begin assessing this risk, we assessed mahaleb sensitivity in an individual with multiple tree nut allergies.

Methods: Indirect ELISA and skin prick testing were used to assess mahaleb sensitivity in a subject with severe nut allergies.  Western blot analysis and indirect ELISA were used to assess in-vitro cross-reactivity between almond and mahaleb protiens.

Results: Skin prick testing and indirect ELISA performed using the subject’s IgG revealed significant reactivity to mahaleb and pistachio, a tree nut unrelated to almond or mahaleb for which the subject had a history of severe allergy. Antigenic similarity between almond and mahaleb was confirmed using indirect ELISA as well as Western Blot analysis using an anti-almond pAb generated by PIBio, whereas little or no activity was seen against pistachio proteins, indicating that the commercial antibody was highly specific for prunus genus seed material.

Significance: The high level of cross-reactivity between almond and mahleb and the clinical presentation of the study subject highlights the need for regulatory bodies and food manufacturers to address the potential for mahaleb contamination in food, particularly foods that are imported from areas where mahaleb is used as a spice.