Cocklebur
Route Of Exposure
Cocklebur is native to Europe, Asia, southern Canada, and most of the United States, Mexico and Central America. Cocklebur is now found worldwide. Another species that is less common but widespread across North America is called Spiny Cocklebur (X. spinosum).
Cocklebur is an annual, grey-green plant, growing up to 1.5m. The plant’s structure is coarse and bushy with stems that are erect, branched, and rigid, with purple or black spots, and very rough. The leaves are lobed, triangular or heart-shaped, coarsely toothed, borne on long stalks, and rough on both sides. Leaves are 5cm to 35cm long, and 2 to 20cm wide.
Cocklebur flowers from July to October and the seeds ripen from August to October. The flowers are monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and are pollinated by insects. The plant is self-fertilising. Male flowers are small and green and hidden at the top of the plant in round clusters. Female flowers occur in burs on short stalks at the base where the leaf axils meet the stem. Each bur contains two flowers. The male flowers drop quickly, while female burs persist, with 2 blackish achenes.
The fruit produced is an elliptic to egg-shaped two-chambered bur, 1 to 3.5cm long, and is covered with about 400 stiff, hooked spines. Two prickles that are longer and wider than the others project from the tip of the bur.
This weed is commonly found in cultivated fields, waste areas, run-down and abandoned pastures, and road ditches. It is poisonous during the two-leafed stage. The burs often become tangled in the fur of grazing animals, thus aiding distribution of the species. Both seeds and seedlings are toxic to livestock.
The seed may be dried, ground into a powder, and mixed with cereal flours during the making of bread and biscuits.
Clinical Relevance
Allergen Description
Cocklebur allergens have not yet been fully characterised. Xan Ib and Xan VIa have been isolated from Cocklebur pollen as the important allergenic components. Xan Ib was found to be devoid of carbohydrate and had a molecular weight of 103 kDa. Xan VIa was a glycoprotein of molecular weight 17 kDa. The carbohydrate moiety of Xan VIa was found to be associated with allergenicity.
Potential Cross Reactivity
Cocklebur is a member of the Ambrosiinae subtribe, tribe Heliantheae, in Asteraceae, as are ragweeds and marshelders. 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. However, despite this close botanical proximity to ragweeds, it was reported that there is little significant cross-reactivity.
However, an earlier study reported that similar antigenic determinants were found between Short Ragweed and Giant Ragweed, Cocklebur, Lamb's Quarters, Rough Pigweed, Marsh Elder, and Goldenrod. Cocklebur and Giant Ragweed were highly potent in their ability to competitively bind to Short Ragweed IgE.
Clinical Experience
IgE mediated reactions
Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are common following exposure to pollen from Cocklebur; however, few specific studies have been reported to date.
In a study in Westchester County in the state of New York of skin prick tests to 48 aeroallergens in100 patients referred for allergic rhinitis, 65% had a positive SPT to at least 1 aeroallergen. Skin prick test for Cocklebur was positive in 3%.
In a study in the Midwestern USA, evaluating the frequency of sensitisation to cannabis pollen, found that 61% were skin prick positive for cannabis and all subjects were also skin test positive to weeds pollinating during the same period: Ragweed, Pigweed, Cocklebur, Russian thistle, Marsh elder, and Kochia.
The incidence of positive intradermal tests after a negative skin prick test for 24 inhalant antigens was conducted on 133 patients in a study in Michigan, USA. Allergens with positive intradermal wheals after negative prick testing included Cocklebur, Rough marshelder, and Ragweed, all with incidences of 16% to 19%.
Common Cocklebur is an important cause of inhalant allergies in Turkey and India.
Other reactions
Cocklebur is a common cause of contact dermatitis.
References
- Jaggi KS, Gangal SV. Purification and characterization of allergens from Xanthium strumarium pollen. Mol Cell Biochem 1987;78(2):177-89.
- Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09.
- Weber RW. Cross-reactivity of plant and animal allergens. Clin Rev Allergy Immunol 2001;21(2-3):153-202.
- 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.
- Guneser S, Atici A, Cengizler I, Alparslan N. Inhalant allergens: as a cause of respiratory allergy in east Mediterranean area, Turkey. Allergol Immunopathol (Madr) 1996;24(3):116-9.
- Basak P, Arayata R, Brensilver J Prevalence of specific aeroallergen sensitivity on skin prick test in patients with allergic rhinitis in Westchester County. Internet J Asthma Allergy Immunol 2008;6(2).
- McKay SP, Meslemani D, Stachler RJ, Krouse JH. Intradermal positivity after negative prick testing for inhalants. Otolaryngol Head Neck Surg 2006;135(2):232-5.
- Stokes JR, Hartel R, Ford LB, Casale TB. Cannabis (hemp) positive skin tests and respiratory symptoms. Ann Allergy Asthma Immunol 2000;85(3):238-40.
- Singh AB, Kumar P. Aeroallergens in clinical practice of allergy in India. An overview. Ann Agric Environ Med 2003;10(2):131-6.
- Singhal V, Reddy BS. Common contact sensitizers in Delhi. J Dermatol 2000;27(7):440-5.
- Nandakishore T, Pasricha JS. Pattern of cross-sensitivity between 4 Compositae plants, Parthenium hysterophorus, Xanthium strumarium, Helianthus annuus and Chrysanthemum coronarium, in Indian patients. Contact Dermatitis 1994;30(3):162-7.
- Guin JD, Skidmore G. Compositae dermatitis in childhood. Arch Dermatol 1987;123(4):500-2.
- Menz J, Winkelmann RK. Sensitivity to wild vegetation. Contact Dermatitis 1987;16(3):169-73.