w16 Rough marshelder
Allergens within Weed Pollens
- Latin name: Iva ciliata/ Iva annua
- Family: Asteraceae
- Common names: Rough Marshelder, Rough Marsh Elder, Annual Marshelder, Annual Marsh-Elder
- Source material: Pollen
Some other members of the genus:
- Iva acerosa - Copperweed
- Iva ambrosiifolia - Ragged Marshelder
- Iva angustifolia - Narrowleaf Marshelder
- Iva xanthifolia - Giant Sumpweed
A weed species producing pollen, which often induces hayfever, asthma and conjunctivitis in sensitised individuals.
Allergen Exposure
Geographical distribution
Rough Marshelder is native to Northern America, in particular to Mexico, and to Nebraska and Texas in the USA. Although some species of the genus Iva have been introduced in other parts of the world, most are found in the North American states of Texas, Louisiana, Mississippi, Oklahoma and Nebraska. Rough Marshelder pollen rivals Ragweed pollen in the Mississippi Delta. Related species are found in Canada and Australia.
Rough Marshelder is an annual weed with fibrous roots, and grows up to 2m in height. It usually reaches half this height. It has an odour like Ragweed and can be mistaken for that weed. The stems are erect, branched, and hairy. The leaves are hairy, opposite, simple, and oval in shape with a pointed tip. They grow up to 15 cm long and 7 cm wide. Each leaf is irregularly toothed.
Flowering occurs from July to October. The flowers are clustered in small heads, each head up to 4 mm long. The heads are in cylindrical spikes in a branched inflorescence, from the leaf axils and terminal. The flowers are green to cream in colour. The flower parts are not discernable with the naked eye. The flowers result in fruits that are 2 to 3mm achenes, dark-brown, flattened, and with a somewhat triangular shape.
Species of Iva differ from species of Ambrosia, the Ragweeds, by having only one kind of flower, as opposed to the Ragweeds' pollen-producing flowers in elongated spikes and pistil-producing flowers in short clusters in the axils of the leaves. Rough Sumpweed differs from other species in the genus by its rough and hairy leaves.
Environment
Marshelder grows in marshy areas, such as wet meadows, prairies, fallow fields and roadsides, stream banks and the shores of ponds and lakes.
Allergens
No allergens from this plant have yet been characterised.
Potential Cross-Reactivity
An extensive cross-reactivity among the different individual species of the genus could be expected, as well as to a certain degree among members of the family Asteraceae (1).
In a study using a fluorescent allergosorbent test, similar antigenic determinants were found between Short and Giant Ragweed, Cocklebur, Lamb's Quarters, Rough Pigweed, Marshelder, and Goldenrod. Cocklebur and Giant Ragweed were highly potent in their ability to competitively bind to Short Ragweed IgE. The other pollens demonstrated lower potency of cross-reacting antigens (2).
Clinical Experience
IgE mediated reactions
Rough Marshelder pollen frequently induces asthma, allergic rhinitis and allergic conjunctivitis in sensitised individuals (3-4).
Of 1159 patients with asthma and allergic rhinitis attending an allergy clinic in Saudi Arabia who tested positive to one or more inhalants, 23.4% were sensitised to Rough Marshelder. The prevalence of sensitisation to this allergen among the 806 Saudi Arabs was 23.4% and among 241 Western expatriates 20.7% (3).
Other reactions
Contact with the leaves may result in contact dermatitis.
References:
- Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
- Perrick D, Stafford CT, Armstrong E, DuRant RH. Modification of the fluorescent allergosorbent test as an inhibition assay for determination of cross-reactivity among aeroallergens. J Allergy Clin Immunol 1991;87(1 Pt 1):98-103
- Suliaman FA, Holmes WF, Kwick S, Khouri F, Ratard R. Pattern of immediate type hypersensitivity reactions in the Eastern Province, Saudi Arabia. Ann Allergy Asthma Immunol 1997;78(4):415-8
- Stokes JR, Hartel R, Ford LB, Casale TB. Cannabis (hemp) positive skin tests and respiratory symptoms. : Ann Allergy Asthma Immunol 2000;85(3):238-240
2002