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|Route of Exposure||Inhalation|
|Latin Name||Paspalum notatum|
|Other Names||Paraguay Paspalum|
Pollen from bahia grass (Paspalum notatum) is an important allergen, especially in the warm subtropical regions. Bahia grass belongs to the tribe Paspaleae of the genus Paspalum. Originally found in Central and South America, it was later introduced to other regions of the world, including North America, Africa, Asia, India, and Australia. Bahia grass is wind-pollinated and presents a prolonged pollination period, from spring through autumn in Australia. Grass pollens of Bahia grass can trigger IgE-mediated allergenic responses like allergic rhinitis and asthma in sensitized individuals. The major allergen identified is Pas n 1 which belongs to group 1 family of allergens. Another allergen identified in Bahia grass is group 13 allergen termed as Pan n 13. Further, Bahia grass shows clinically relevant cross-reactivity with pollens of other temperate grasses.
Bahia grass (Paspalum notatum) is a perennial grass growing in bunches. It thrives well in warm-seasons and is deep-rooted. It exhibits sod-forming properties. Bahia grass propagates vegetatively by runners and root stalks (1, 2). It usually exists in two types: diploid and tetraploid varieties. The diploid variety reproduces sexually whereas the tetraploid variety reproduces asexually by unfertilized, viable seeds (3). The tetraploid type is the common variety (P. notatum) while the diploid type is the saurae variety (Penascola type) with different morphological characteristics. They can be differentiated as the common form is comparatively shorter and has broad leaves and short internodes than saurae variety (1, 4). The stems usually grow 20 to 75 cm in height. The leaves are long (6-25 cm) with a flat base and tapering ends (1, 2).
The central axis continues to grow, and flowers are borne on the lateral axes having a spike inflorescence (1, 2). The flowering season and the pollination period of Bahia grass are very long extending from May till October in the Gulf states while from spring through autumn in Australia (2, 5). The robust woody rhizomes and comparatively narrow leaves distinguish P. notatum from other Paspalum species (1).
Paspalum is a large genus with around 310 species (3). Bahia grass belongs to the subtropical grass clade (PACMAD) and tribe Paspaleae of this genus Paspalum. Other grasses under this tribe with allergenic pollens are P. distichum (water couch) and P. dilatatum (Dallas grass) (6).
|Taxonomic tree of Bahia grass (6,7)|
Bahia grass pollens are round (32-45 µm diameter) with a thick cell wall (2, 5, 8). They have a single circular pore of 3.4-5.1 µm diameter. It has an entangled texture of the outer surface (2). Pas n 1, a β-expansin, has been identified as an allergenic molecule from this pollen (9).
The Pooideae grasses are abundantly found in parts of Africa, India, Asia, Australia, and America (6) and the pollen of Bahia grass is prominent in some regions, like subtropical Australia, Gulf states, and Cuba. It is considered as one of the major allergies (rhinitis) causing pollens in these regions (2, 10).
Sensitization to Bahia grass pollen also seems to be a major problem in the United States (US) pediatric population. With a sensitization rate of 38 % amongst military children with allergic rhinitis (AR), pollen from Bahia grass was shown to be the most frequently affecting grass pollen (11).
Also, in other parts of the world, sensitization to Bahia grass pollen has been reported to be of significance. A retrospective cross-sectional study in Argentina found that 69% of 894 patients with seasonal AR were sensitized to extracts of Bahia grass along with Sorghum halepense (12).
A study conducted in New South Wales, Australia found a 31.6% prevalence of sensitization for Bahia grass among 206 residents (13). Another study in Australia found that 85% of 34 grass pollen allergic patients with seasonal rhinitis were sensitive to Bahia grass pollen (5). Further, a retrospective (2001-2014), cross-sectional multicenter study in Sydney, Australia reported 43.8% of 755 patients sensitized to Bahia grass aeroallergen based on positive skin prick test (SPT) (14). In Victoria, a temperate region of Australia, 78% of patients with seasonal rhinitis, with or without asthma, who were allergic to grass pollens, tested positive for the SPT to Bahia grass (15). In a subtropical region in Brisbane, Australia, SPT, and plasma IgE reactivity in the 233 patients included in a study were significantly higher (p<0.0001) with Bahia grass pollens than the Johnson grass, Bermuda grass or Ryegrass pollen (16).
Although Bahia grass is a subtropical grass species, it has been extensively introduced in the tropical and warm-temperate regions of the world. In Asia, Africa, Europe, Australia, and the Pacific, it is used as a forage and turf grass, as a ground cover and is also used to control soil erosion (4, 5, 17). It can grow well on moist soils (8) and is adaptable to sandy as well as marginally fertile soils (1).
Bahia grass is one of the major components of the grasslands of the earth’s western hemisphere (6). Bahia grass is found to be distributed throughout America (North, Central, and South). It was initially found widespread in Brazil, Paraguay, Uruguay, and Argentina. Later, it spread and naturalized throughout the US (1). At present, Bahia grass is abundant in temperate and subtropical regions of America in addition to some parts of Africa, Australia (New South Wales and Queensland), and Asia (2, 6, 17). Both the varieties of this grass are now found in Australia (1, 18). Besides, Bahia grass is also found in Asian regions like India, Japan, Taiwan, and Zimbabwe (1, 6). It is a clinically significant source of grass pollen allergen in the southern USA and Australia (6).
Pollens from Bahia grass can enter the respiratory tract through inhalation. They can induce allergic reactions like allergic rhinitis and asthma, either by encountering the nasal mucosal surface or by inhalation of allergen particles (reduced size by hydration of pollen grain) (5, 19).
The pollens of Bahia grass can provoke IgE-mediated type I hypersensitivity reactions in sensitized individuals (8).
Pollinosis, commonly known as seasonal AR, is caused by Bahia grass allergens in individuals who are sensitive to its pollens. AR or allergic rhino-conjunctivitis symptoms are seen once the allergen comes in contact with the mucosa of the airway and the conjunctiva in patients who were previously sensitized to these allergens (19). It is also considered a major trigger for AR in Australia, especially in subtropical regions like Brisbane where this grass is dominant (18).
It was found to be statistically associated [Odds ratio (OR)-14.47, Confidence Interval (CI) – 1.99-298.21] in a study conducted on 153 atopic patients sensitive to one or more aeroallergens in New South Wales, Australia (13). In a study on 18 Bahia grass pollen allergic patients in Melbourne, Australia, all the patients were clinically diagnosed to have allergic rhinitis (17).
A study in Australia found that an increase in the concentration of grass pollens including Bahia grass, in the atmosphere was linked with a considerable increase in the visits to the hospitals' emergency department and increased admissions for asthma. This was attributed to Bahia grass and Bermuda grass pollens especially in subtropical regions like Brisbane where these grasses are dominant (18).
A study in New South Wales, Australia conducted on 21 atopic children sensitive to one or more aeroallergens, observed a statistically significant association (OR – 12.00, CI – 1.06-315.54) between Bahia grass and asthma in children (13). Bahia grass pollen sensitization was found in 28% of 99 patients with acute asthma in Cartagena, Colombia (20). Further, another study on 31 Bahia grass pollen allergic patients in Australia found that 17% were showing symptoms of asthma (5). Similarly, another study in Melbourne Australia reported only 33% of 18 Bahia grass pollen allergic patients suffering from asthma (17).
Bahia grass pollens comprise several proteins. However, only 4 of them have shown allergenic reactivity. The four allergenic proteins are estimated to have molecular weights of 45, 33, 31 and 28 kDa. It was also found that deglycosylation of these allergenic proteins did not abolish the IgE reactivity (8). However, currently, only one of these proteins has been listed officially in the database of the World Health Organization/International Union of Immunological Studies (WHO/IUIS) Allergen Nomenclature Sub-Committee (9).
The table below provides detailed information on the allergenic protein identified by WHO/IUIS:
|Allergen||Biochemical Name||Molecular Weight (kDa)||Allergenicity|
|Pas n 1||β-expansin||
kDa: kilodaltons, IgE: Immunoglobulin E, ELISA: Enzyme-linked Immunosorbent Assay
Besides the above published allergens by WHO/IUIS, another protein of group 13 allergen has been identified, termed as Pas n 13. It was reported to be a polygalacturonase with 50-55 kDa molecular weight. The IgE reactivity on ELISA with Pas n 13 was observed to be 48% in 71 grass pollen allergic patients. It was able to activate basophils in grass pollen allergic patients in low concentrations suggesting its role in allergic reactions like AR or asthma in sensitized individuals (6, 23).
Cross-reactivity between Chloridoid (such as Bahia grass and Bermuda grass) and Pooid (such as perennial ryegrass, timothy grass, and Kentucky bluegrass) members have been observed (22, 24). Part of the cross-reactivity may be attributed to the major allergen Pas n 1 that has been shown to cross-react, at the T-cell level, to another group 1 grass pollen allergens like Lol p 1 (ryegrass) and Cyn d 1 (Bermuda grass) (17). Pas n 1 has shown homology to other group 1 allergens like maize (85%), ryegrass or timothy grass (64-66%), and Johnson grass (63%) (2, 5). However, since unique epitopes are present in subtropical grass pollen allergens that are not found in temperate grass pollen allergens, the overall cross-reactivity is usually considered to be limited. This was confirmed by a study that reported that extracts of temperate (Ryegrass and Timothy) grass pollens are unable to completely inhibit IgE reactivity of pollen extracts of subtropical species (Bahia, Johnson, and Bermuda grasses) (16). It was found that IgE reactivity with Bahia grass pollen (Pas n 1) was also inhibited by Lol p (Lolium perenne), Phl p 1 (Phleum pratense), Sor h (Sorghum halepense) and Cyn d 1 (Cynodon dactylon) (22).
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Christian Fischer
Last reviewed: January 2021