Salt grass

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Code: g203
Latin name: Distichlis spicata
Source material: Pollen
Family: Poaceae (Gramineae)
Sub family: Pooideae
Tribe: Poeae
Common names: Salt grass, Seashore Saltgrass, Inland Saltgrass, Alkali Saltgrass, Alkali-grass, Spike grass

Pollen

A grass species producing pollen, which may induce hay fever, asthma and conjunctivitis in sensitised individuals.

Allergen Exposure

Geographical distribution

Within its specialised saline and alkali environments, Salt grass is widely distributed across the western United States and Canada, from Saskatchewan to eastern Washington; and south, to California, Texas, and Mexico.

Distichlis spicata is a tough, warm-season perennial grass species that grows 10 to 60cm tall and spreads through extensive scaly rhizomes. The small blue-green to grey-green leaves are sharp-pointed, coarse, and spread along the entire rigid stem, on opposite sides of which they stand erect, in two rows. They turn golden brown at the end of the growing season. The species is easy to recognize even in the winter, because the leaves (though dry) remain attached.

Plants are dioecious (male and female flowers are on separate plants). The male panicle often extends above the leaves, but the female panicle is normally enclosed within the leaves. Panicles of both sexes are 4 to 8cm long, with only a few spikelets. The tan, flattened and overlapping spikelets contain about five flowers each. Salt grass is a poor seed producer. Reproduction is mainly vegetative; plants spread through a well-developed system of rhizomes.

Environment

Salt grass grows on beaches, along estuary margins, at the edges of desert palm oases, in salt and brackish coastal marshes – where it can form large monocultures (dense mats) – and in other low, moist, saline or alkaline environments (1).

Allergen Description

The following allergens have been characterised:

Dis s 1, a 27-35 kDa Group 1 Grass allergen (2).

Dis s 7, an 8-12 kDa protein, a calcium binding protein (CBP) also known as polcalcin (3, 4).

Potential Cross-reactivity

Extensive cross-reactivity among the different individual species of the genus may be expected, as well as among members of the family Poaceae to a certain degree, especially in the tribe Poeae (Cocksfoot (g3), Meadow Fescue (g4), Rye grass (g5), Meadow grass (g8)) (5, 6).

It has been suggested that Chloridoideae (Salt grass, Bermuda grass, and grama grass) and Panicoideae (Bahia grass and Johnson grass) have little to no cross-reactivity between pooid and chloridoid pollen while the panacoid grasses show moderate cross-reactivity with both the pooids and chloridoids (7).

Clinical Experience

IgE-mediated reactions

Anecdotal evidence suggests that Salt grass pollen may occasionally induce symptoms of asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals; however, no studies have been reported to date.

Compiled by Dr Harris Steinman, developer of Allergy Advisor, http://allergyadvisor.com

References

  1. Lewis WH, Vinay P, Zenger VE. Airborne, and Allergenic Pollen of North America. Baltimore: Johns Hopkins University Press 1983:117.
  2. Smith PM, Avjioglu A, Ward LR, Simpson RJ, Knox RB, Singh MB. Isolation and characterization of group-I isoallergens from Bermuda grass pollen. Int Arch Allergy Immunol 1994;104(1):57-64.
  3. Smith PM, Xu H, Swoboda I, Singh MB. Identification of a Ca2+ binding protein as a new Bermuda grass pollen allergen Cyn d 7: IgE cross-reactivity with oilseed rape pollen allergen Bra r 1. Int Arch Allergy Immunol 1997;114(3):265-71.
  4. Wopfner N, Dissertori O, Ferreira F, Lackner P. Calcium-binding proteins and their role in allergic diseases. Immunol Allergy Clin North Am 2007;27(1):29-44.
  5. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala, Sweden. 1982: ISBN 91-970475-09.
  6. Yman L. Pharmacia: Allergenic Plants. Systematics of common and rare allergens. Version 1.0. CD-ROM. Uppsala, Sweden: Pharmacia Diagnostics, 2000.
  7. Esch RE. Grass pollen allergens. Clin Allergy Immunol 2008;21:107-26.

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.