g71 Canary grass

Phalaris arundinacea (canary grass) is a widely distributed perennial wetland reed with highly-mobile pollen that can induce hypersensitive respiratory and cutaneous reactions in sensitized individuals. 

Worldwide distribution 

P. arundinacea is a perennial wetland reed which is widely distributed throughout North and Central America, most of Africa, Europe, the Middle East and Asia, including Pacific islands (1).

Considered an invasive species, canary grass grows 0.6–2 m high and can spread rapidly along watercourses and ditch systems (1). The invasive success of canary grass may be related to its highly plastic phenotypic responses to environmental stresses (5, 6), and a number of studies have demonstrated a beneficial ecological role for P. arundinacea in phytoremediation of contaminated soils (7, 8), denitrification (9) and greywater reuse (10).

Main 

Large quantities of highly mobile seed are produced in the first year of life, and canary grass also spreads vegetatively via vigorous and dense rhizome growth (1, 3, 6). Direct exposure of skin to grass has been reported to elicit hypersensitivity reactions including itchy urticaria and angioedema (3).

A retrospective cross-sectional study of 894 patients with seasonal allergic rhinitis in Argentina assessed skin prick tests (SPTs) to selected pollen species belonging to three subfamilies of the Poaceae family, which between them account for 95% of allergy-relevant grass species (2). In this study, patients were most frequently sensitized to extracts from the Pooideae subfamily (86.8%; CI 84.4%–88.9%), and P. arundinacea (subfamily Pooideae) presented the highest frequency of sensitization of all species tested overall (62.2%; CI 59.0%–65.3%) (2).

Ramon et al. (2017) described a 4-year old male child who developed acute urticaria and mild neurologic/respiratory symptoms after exposure to grasses including P. arundinacea (3). On two occasions, the child laid down on grass and within several minutes experienced generalized itching, angioedema, erythema and respiratory symptoms which resolved following treatment with glucocorticoids and/or antihistamines (3). Notably, SPTs for this child were negative for a broad range of foods and airborne allergens but significantly positive for three grasses including P. arundinacea (3).

Luis et al. (2017) described two case reports of patients with a personal history of seasonal allergic rhinoconjunctivitis and asthma to pollen, who developed perennial symptoms after keeping parakeet birds at home (4). SPTs in both patients were positive to a range of seed and grass substances including canary grass, and the authors concluded that asthma and rhinoconjunctivitis after inhalation of bird food were rare but should be considered as a potential cause of respiratory allergy in bird-keepers (4).

Allergenic molecules

To date, no allergens have been characterized from P. arundinacea specifically.  However, several protein allergens have been isolated from the pollen of P. aquatica, a closely-related bulbous canary grass, which suggests these allergens may be present in P. arundinacea (11, 12):

·       Pha a 1, a 34 kDa protein and major Group 1 allergen

·       Pha a 5, a major Group 5 allergen with four isoforms

Cross-reactivity

Variable degrees of cross-reactivity may occur between grass pollen species sharing Group 1 and/or Group 5 grass allergens (13). Radioallergosorbent testing (RAST) of sera from subjects sensitized to inhaled wheat or flour indicated that there was significant reaction with seed extracts of 12 different cereals, including canary grass (14).

Carbohydrate-reactive IgE antibodies attributed to grass pollen sensitization have been found to cross-react with glycan structures from other allergen sources, particularly vegetable foods (15). Extensive cross-reactivity is also possible between profilins, a family of Group 12 allergen proteins which are highly conserved throughout the plant kingdom and present in all tissues (15).

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

Last reviewed: December  2021