Macadamia nut
Summary
Macadamia nuts are white seeds or shelled kernels from an evergreen Australian native tree Macadamia spp. especially integrifolia or tetraphylla belonging to the family Proteaceae. They are increasingly being used in the form of dried and roasted nuts in food due to its unique flavors, multipurpose uses and long shelf life. Macadamia nut allergy is less common than other tree nut allergies, but it is included in the collection of nine nuts that accounts for the majority of the tree nut allergies globally. The prevalence of the tree nut allergy including macadamia varies according to region, age and diagnostic definition in different countries. Cases of oral ingestion of macadamia nut have been reported to cause allergic reactions ranging from pollen food allergy syndrome to severe reactions like anaphylaxis. There is a paucity of information on corresponding allergens which may be seed storage proteins. Macadamia nuts are found to be cross-reactive to other tree nuts like hazelnuts, walnuts, cashew nuts, or pecan nuts with co-existent allergies. The only effective approach for this allergy is to avoid the consumption of tree nuts or food products containing them.
Epidemiology
Worldwide distribution
Macadamia nut allergy is less common than other tree nut allergies. It is reported to be <5% in tree nut allergic individuals in the US. However, certain case reports of macadamia nut allergic reactions ranging from pollen food allergy syndrome to severe reactions are present.
Macadamia was responsible for allergy in only 14 out of 122 nut allergic participants in a study in the UK where the consumption of macadamia nuts was 1%. A review evaluated the prevalence of tree nut allergies to nine specific tree nuts i.e. walnuts, almond, pistachio, cashew, pecan, hazelnut, Brazil nut, pine nut and macadamia nut. The prevalence of tree nut allergies including macadamia in Europe, confirmed by oral challenge, was found to be ranging from 0 to 4.3%. These studies were mainly including children with only one study in adults. The US-prevalence data showed 0.5% in adults and 1.1% in children based on telephone surveys while Canada showed a prevalence of 1.7% in children and 1% in adults. Australia reported a prevalence of 2.3% in school children of 10-14 years old while 0.32%, 0.28% and 0.3% were reported in Korean, Philippines and Singapore school children respectively. This confirms that tree nut allergy including macadamia varies according to region, age and diagnostic definition.
The use and demand for macadamia nuts are increasing throughout the world due to their unique flavors, multipurpose uses and long shelf life.
Route Of Exposure
Main
Oral ingestion of macadamia nuts can trigger oral food allergy or anaphylaxis like symptoms. Fresh macadamia nut is thought to be responsible for allergic responses.
Clinical Relevance
Systemic IgE-mediated reactions
Macadamia nut allergy report symptoms ranging from oral allergy syndrome to severe reactions. Certain cases have reported macadamia nut allergy as anaphylaxis or severe symptoms.
Severe reactions like generalized pruritis, throat itching, rhinitis, dyspnoea, dizziness, severe oral burning, and swelling were seen in two cases of 42-year and 34-year old males. Cases of anaphylaxis were also reported presenting as severe erythema, generalized urticaria, tongue and throat swelling, swelling in the eyes, dyspnoea, wheezing and hypotonic circulatory reaction along with severe erythema and periorbital angioedema in 1-year old.
Prevention And Therapy
Prevention strategies
Avoidance
Tree nut allergies usually develop during childhood but are considered to be life-long and the likelihood of its resolution is only about 10%. The only effective approach to this date is avoiding the consumption of tree nuts or food products containing them. Due to this, USFDA and European Union have made it mandatory to mention allergenic substances on the food label which included tree nuts like macadamia too.
Cross-Reactivity
Macadamia nuts are found to be cross-reactive to other tree nuts like hazelnuts, walnuts or pecan nuts with co-existent allergies. The probable allergen responsible for cross-reactivity with hazelnut is thought to be a 17 kDa protein. Cross-reactivity with cashew nuts has also been described. Usually, patients with peanut allergy are advised to avoid all tree nuts due to cross-reactivity. However, 97% of peanut-allergic patients depicted a negative skin prick test with macadamia. A recent retrospective study in the Midwestern United States found that a high rate of co-sensitization (77%) exists between macadamia tree nuts and coconut.
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