Coconut
Summary
Coconut (Cocos nucifera) belongs to the genus Cocos and Arecaceae family. It is a synoicous plant that can grow around 72 ft and is found commonly along the tropical, subtropical, and coastal areas worldwide. Coconut plant comes from the tropical regions of Latin America, Africa, and the Asia-Pacific region. Coconut is used worldwide for various purposes like for cooking, as a medicine, for dermatology products, and for making handicrafts. Coconut contains multiple allergens such as Coc n 1 (7S globulin), Coc n 2 and Coc n 4 (11S globulin) protein. Coconut allergy is a rare phenomenon, but it can lead to conditions such as bronchial asthma, contact dermatitis, allergic conjunctivitis, and anaphylaxis. Immunotherapy is effective in reducing symptoms of coconut allergy. Cross-reactivity is observed between coconut and macadamia, almond, walnuts, hazelnuts and lentils, latex, and this is mainly due to allergens such as 7S and 11S globulins.
Epidemiology
Worldwide distribution
Only some case reports of a severe allergy to coconut have been reported to date in the literature. In an Australian survey, including 5000 patients suspected of food allergy, nine had suffered anaphylaxis reaction, and 26 had milder IgE-mediated allergy from coconut ingestion.
A study was conducted in the United States to know the prevalence of coconut allergy in children suspected of tree nut and peanut allergy. A total of 37 children were tested for coconut skin prick test (SPT). The results showed that out of 37 children, 21.6% were sensitized to coconut, and 24% were diagnosed with coconut allergy. Coconut allergy increment in tree-nut or peanut-allergic children was not observed in the study.
In another study, 5843 children’s food IgE data was used to derive patients questioned for coconut IgE in the US. Among these, 298 patients underwent coconut IgE testing, where 30.2% were observed to have positive coconut sIgE testing results. Significant correlation between coconut, and two tree nuts that are macadamia and almond, was observed. While in all other nuts, the relation was observed to be not statistically significant. Anaphylaxis reactions and oral allergy syndrome were also observed in patients allergic to coconut with a walnut allergy history.
A study was conducted in Southern India on individuals (n=2219) diagnosed with asthma and allergic rhinitis. Among these, 9.4% (209/2219) showed positive skin prick test results to coconut.
Route Of Exposure
Main
The main route of exposure for coconut pollen is through ingestion.
Secondary
Allergic patients may suffer from skin reactions due to coconut exposure through cutaneous pathways, like applying oil to the skin.
Coconut Pollen can be inhaled by an individual and lead to an allergic reaction.
Clinical Relevance
Coconut allergy is an infrequent clinical entity. In the small number of cases that have been reported, most of them are associated with anaphylaxis. Other symptoms observed are urticaria, dermatitis, asthma and rhinorrhea.
Studies have shown that exposure to coconut and its allergens may facilitate the risk of coconut sensitization from a young age even after tolerance to coconut in initial years. This exposure may also lead to an increment in allergic reactions with aging in allergic patients.
Anaphylaxis
In Spain’s published literature, around nine allergy cases to coconut with anaphylactic reaction have been reported. Among these, four of them occurred in children. The patients may suffer from allergic reactions such as rhinorrhea, sneezing outbursts, spasmodic coughing, vomiting and breathing difficulty.
A boy (age three years) suffered from, oral allergy syndrome, vomiting, sudden abdominal pain and eyelids’ edema after ingesting a small portion of fresh coconut. No other food allergies were present. A skin prick test with coconut showed a strong positive response. Testing with sIgE to coconut was also positive.
Contact Urticaria
A literature published case report on mono-sensitization to coconut in a 64-years-old female patient suffering from hypertension and thyroiditis. The patient developed generalized urticaria, facial and uvula edema, dysphagia and dyspnea. Another episode followed where hypoxemia (low oxygen levels), hypotension (low blood pressure), and bronchoconstriction reactions were observed.
Atopic Dermatitis
Coconut fatty acids diethanolamine is a by-product of coconut oil. In a study conducted on a total of 2572 subjects with occupational allergic contact dermatitis, around 1 percent had allergic dermatitis due to coconut products.
Allergic conjunctivitis
A case of occupational allergic conjunctivitis due to coconut fiber dust was reported. A 46-year-old male had been working for about ten years in the factory of coconut fibre mattress. He developed conjunctivitis in the last few years, usually appearing 20 to 30 minutes after tufting of coconut fibre mattress. On the application of the coconut fibre test, he developed symptoms of allergic conjunctivitis. The signs were seen up to 24 hours after the test. An increase in eosinophil count was also found in tear fluid from the patient.
Asthma
In a study done in India in 975 individuals, about 2% of patients with coconut sensitivity had asthma and allergic rhinitis. A positive result was found in seven out of a total of eight patients in a test of bronchial provocation.
Prevention And Therapy
Allergen immunotherapy
In a placebo-controlled study conducted in 96 coconut allergic patients for a 6 to 12 months period, the results showed a statistically significant (p< 0.005) reduction in symptoms and drug use in the immunotherapy group as compared to placebo.
Prevention strategies
Avoidance
Allergic reactions to coconut can be prevented by avoiding the allergenic food made by coconut and products created in the near vicinity of coconut products.
Cross-Reactivity
Cross-reactivity has been found between coconut and tree nuts such as walnuts, hazelnuts and lentils, and this is mainly due to allergens such as 7S and 11S globulins. The coconut’s decreased protein at 35 kDa of coconut 11S globulin is thought to be soy glycinin, a legumin type of seed storage protein. In a study of two subjects with an allergy to coconut, the clinical reactivity was found due to cross-reactivity of IgE antibodies for Walnut. 7S globulin, which has been described as a major allergen in walnut (Jug n 2, Jug r 2) and hazelnut (Cor a 11), is also identified in coconut.
Though in general correlation between patients sensitized or allergic to tree-nut or peanuts with sensitization to coconut has not been observed. One study in the children population reported high significant coconut co-sensitization rates with 71% for macadamia and 69% for almond. In another case report, two patients, who had a history of anaphylactic reaction to walnut, developed an anaphylactic reaction to coconut, signifying co-sensitization.
There also exists cross-reactivity between latex and coconut. In a study done in patients with type I latex allergy, about 21.1% of them had a food allergy. Out of these, about 2% had coconut allergy.
A study has discovered strong cross-reactivity between buckwheat and coconut. This cross-reaction may be due to Coc n 2 of molecular weight 29 kDa in coconut and Fag e 3 of 19 kDa in buckwheat, known as vicilin-like allergens.
References
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