Pear
Summary
Pear (Pyrus communis, P. pyrifolia/sinensis) is a fruit of the Rosaceae family and grown in many countries. There are many different cultivars, which vary in appearance. Peel and flesh of the fruit are the main sources of hypersensitivity and allergic reactions, though pollen may also be implicated in allergies. Several pear allergens have been described.
Pollen-food allergy syndrome (PFAS) and one of its common presentations, oral allergy syndrome (OAS) is a common clinical presentation of pear allergy, with symptoms ranging from localized to systemic, including anaphylaxis. Contact dermatitis and seasonal allergy may also be a clinical presentation of pear hypersensitivity. Cross reactivity with several other plant food and pollen allergens may occur.
Epidemiology
Worldwide distribution
Pear allergy has been reported in a number of countries, including Japan, The Netherlands, China, and Spain.
Risk factors
Certain occupations handling pears may pose risk of contact dermatitis.
Consumption of unpeeled pear may be a trigger for allergic reactions.
For patients suffering from pollen-food allergy syndrome (PFAS), the season of pollination of the plants they are allergic to is more likely to trigger food allergy symptoms. In specialized orchards, where pollination is carried out by operators, exposure to pear pollen (in this case, P. pyrifolia) is able to cause sensitization and symptoms of seasonal allergies.
Route Of Exposure
Main
Ingestion of the fruit, peel, contact with pear proteins.
Clinical Relevance
Allergic rhinitis
Chronic rhinosinusitis with nasal polyps (CRSwNP) could be associated with food allergies; both asthma and allergic rhinitis are often comorbidities in people with food allergies, due to cross-reactivity between aeroallergens. A study showed that in patients with CRSwNP, IgG to certain types of foods (including pears and apples) were significantly reduced, irrespective of consumption. The authors suggested this might be due to IgG responses deviated towards other allergens.
Atopic Dermatitis
Contact dermatitis from pear proteins, at times also causing urticaria.
Other diseases
OAS (considered a manifestation of pollen-food allergy syndrome), consisting of IgE-mediated allergy symptoms limited to the oral cavity, is another presentation of pear allergy. The symptoms can start within minutes of consuming the sensitizing food. Clinical presentation is variable; normally limited to oral cavity with itching/burning sensation of lips, mouth, ear and throat, perioral erythema, urticaria, anaphylaxis. There may be swelling in the face, a sense of suffocation, hypotension and digestive symptoms. Another study using two varieties of pear in a single-blind oral challenge study reported symptoms of itchy mouth, itchy nose and ears, nausea, wheezing, skin and laryngeal symptoms.
In patients that have no history of pollen allergies, anaphylaxis is a severe presentation of food allergy to Rosacea fruits, including pear; 82% of patients reported systemic symptoms, with anaphylactic shock recorded in 36% of patients.
Diagnostics
Testing for food allergies involves measuring serum specific IgE responses, skin prick tests (SPTs) and oral challenges. A Multiple Allergen Simultaneous Test-Chemiluminescent Assay (MAST-CLA), measuring specific IgE, may also be used to diagnose hypersensitivity to Rosacea plant foods, although its usefulness regarding pear hypersensitivity is lower than for apple.
In a study of 36 patients with symptoms of OAS following ingestion of Rosacea fruits, half were split into the birch pollen-allergic group, and the other half to non-allergic. It was shown that for the birch pollen-allergic patients, SPTs were a reliable method to diagnose fruit hypersensitivity. However, for those patients not allergic to birch pollen the SPTs are best carried out with fruit peel extracts.
In another study which involved patients with known pollen allergies, pear was the third most common Rosacea fruit causing hypersensitivity, with 26.6% of positive SPTs. A similar study on 129 patients, 83 of which with PFAS and the remaining suffering from seasonal pollen allergies without food component, showed that pear was again the third most common fruit reported as cause of hypersensitivity reactions.
A blind oral challenge was carried out in 15 birch pollen-allergic patients with a known history of pear allergy; in this study, two different pear varieties were used. All patients were sensitized to one or both pear varieties, as shown by specific IgE testing, SPT, prick-to-prick (PTP) tests and the oral challenge. Analyzing the pattern of responses to the two varieties, the study concluded that for some patients with pear hypersensitivity it may be possible to consume certain varieties outside of the birch pollination season.
Cross-Reactivity
Cross-reactivity between members of the Rosaceae family has been reported. Apple, peach and pear share cross-allergenic components. Birch pollen contains allergens cross reactive with Rosacea plants; the allergen Bet v 1 is related to the pear Pyr c 1. Pyr c 1 is also related to Mal d 1 from apple. Pyr c 4 (profilin) showed a strong cross-reactivity with birch pollen antigen Bet v 2 and with mango profilin. The peach skin LTP allergen Pru p 3 may cause sensitization to the pear homolog.
References
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