Summary

Melon (Cucumis melo) is a fruit grown worldwide and is part of the Cucurbitaceae family. There are many different cultivars, which vary in appearance, flavor and uses. Peel and flesh of the fruit are the sources of hypersensitivity and allergic reactions; one melon allergen (Cuc m 2), a profilin, is considered a pan-allergen due to its common presence in the plant world.

Pollen-food allergy syndrome (PFAS) and one of its common presentations, oral allergy syndrome (OAS) are the main clinical presentations of melon allergy. Symptoms tend to remain limited to the oral cavity; however more severe systemic reactions have also been described. Cross reactivity with a number of other plant food and pollen allergens usually occurs.

Epidemiology

Worldwide distribution

Symptoms of allergic disease to melon have been studied in different countries, including Spain, Korea, USA and several Southern European countries. Profilin (a major melon allergen) sensitization is present in 15–50% of patients with pollen-food syndrome from different European and American areas.

Risk factors

Pollen allergies (due to the pan-allergen profilin) represent a risk factor for melon allergy. Profilin sensitization alone is considered a risk factor for asthma, and of increased severity of allergic disease when in association with other allergens. Southern European ethnicity may be a risk factor.

Route Of Exposure

Main

Ingestion.

Secondary

Skin contact.

Clinical Relevance

Various studies have shown that patients with melon allergy were also sensitized to other foods (Cucurbitaceae, avocado, banana, chestnut, tomato, pineapple, peach, papaya, fig and kiwi), or had symptoms of pollen allergy, asthma, seasonal rhinitis and/or latex sensitization. Systemic allergic reactions to melon alone are considered rare.

Atopic Dermatitis

Melon peel can cause contact allergy with symptoms of angioedema and urticaria.

Other diseases

OAS, consisting of IgE-mediated allergy symptoms limited to the oral cavity, is a common presentation of sensitization to melon. Symptoms may present as tongue and pharyngeal pruritus, tongue angioedema, generalized oral pruritus, lip angioedema and facial erythema. In a study of 161 patients, of which 66 had confirmed melon allergy, 100% had oral symptoms, 19.7% had extra-oral symptoms and none had generalized urticaria or anaphylaxis. Other observed symptoms of melon allergy included facial angioedema, rhinoconjunctivitis and wheezing; additionally, severe systemic reactions suggestive of anaphylaxis were recollected when taking patient history (oropharyngeal symptoms, generalized urticaria and angioedema, nausea/vomiting, hypotension and wheezing).

PFAS is a wider term that spans OAS and systemic symptoms, arising from exposure to certain foods that share allergens with plant pollens. A study of 648 patients with symptomatic pollen allergies (allergic rhinitis, allergic conjunctivitis and/or bronchial asthma), showed that 41.7% of them had PFAS. Melon hypersensitivity caused 11.5% of PFAS cases. The symptoms following exposure to the allergenic foods (including melon) varied from anaphylactic reactions (8.9%), respiratory symptoms (20%), cutaneous symptoms (43%) and cardiovascular or neurological symptoms (less than 5%). In another study, 815 patients with seasonal allergic rhinitis were examined; 20.5% reported PFAS symptoms, of which melon caused 15.6%.

Diagnostics

Testing for food allergies involves measuring serum specific IgE responses, skin prick tests (SPTs) and oral challenges.

In a study of 53 patients with a history of adverse reactions to melon ingestion, 68% had positive SPTs and 43% showed positivity for specific IgE; the overall clinical reactivity to food challenges was 36%. Significant differences may arise between results of SPTs, oral challenges and in vitro tests; therefore it is recommended that oral challenges should be included in latex-fruit allergy diagnostics.

Prevention And Therapy

Allergen immunotherapy

A 34-year old patient with pollen allergies and OAS following ingestion of fennel, cucumber and melon was able to tolerate fresh melon at oral challenge after 43 months of injectable immunotherapy containing grass pollen extracts.

Prevention strategies

Avoidance consists of eliminating melon (and other foods causing similar symptoms) from the diet, once accurately diagnosed. If a patient is allergic to the peel of a Cucurbitaceae, it is recommended that they avoid touching and eating the peel of other plants of the same Family.

Cross-Reactivity

Cross-reactivity has been shown with allergens from other plants. Nonspecific lipid transfer protein (nsLTP) from melon peel is cross reactive with nsLTPs from the peel of other Cucurbitaceae, as shown by binding of IgE from the serum of two patients with confirmed melon allergy. Other putative allergens were identified by sequence alignment and structural analysis using Cuc m 1, Cuc m 2 and Cuc m 3 sequences to mine the genome of other Cucurbitaceae. Latex is another plant-derived substance that is known to cross-react with plant foods, most likely due to the high sequence similarity of its profilin to other sources. Examples of allergenic profilins from other plants include Art v 4 (mugwort pollen), Bet v 2 (birch pollen), Phl p 12 (timothy grass), Ole e 2 (olive pollen), Cit s 2 (oranges) and Mus a 1 from bananas.