Willow
Summary
Willow trees (Salix caprea) are distributed across temperate regions of Europe, North America, western temperate Asia and north-east Africa. Salix pollen is a minor to moderate allergen source causing allergic rhinitis and asthma. Willow pollen shows cross-reactivity with other members of the Salicaceae family (mainly poplars) and with beech.
Epidemiology
Worldwide distribution
In a review of 36 publications of pollen allergy in the Middle East, an average of 10.9% of the study populations were allergic to willow pollen.
Pediatric issues
In a US study of 123 children aged 2-8 years with allergic rhinitis, willow was a significant sensitizing allergen, with the highest prevalence in children ages 2-3 years.
Route Of Exposure
Main
The main route of exposure is inhalation.
Clinical Relevance
Salix pollen is associated with allergic rhinitis and asthma. It has been considered a minor allergen source due to its low airborne pollen counts. However, in regions where willow trees are common, airborne pollen loads may be sufficient to cause significant allergen sensitization. Salicaceae species were among the ten most allergenic tree pollens described in a review of common tree pollens in the Middle East. In a study of 866 allergic Turkish patients, 45.8% showed a positive skin prick test to Salix caprea.
Diagnostics
Willow pollen is sampled using a volumetric trap such as the Hirst-type pollen trap.
Prevention And Therapy
Prevention strategies
Avoidance
Allergenic vegetation maps may contribute to allergy risk assessments by showing the location of willow trees at 1 km resolution. They can be combined with health data to inform allergy research, or with weather data to improve pollen forecasting or to generate pollen emission models.
Cross-Reactivity
Strong cross-reactivity between pollens has been reported, as well as moderate cross-reactivity between Salicaceae and Fagales (beech)
References
- LOINC. Willow (Salix caprea) 2021 [cited 2021 18.11.21]. Available from: https://loinc.org/LP13974-8/.
- Costache A, Berghi ON, Cergan R, Dumitru M, Neagos A, Popa LG, et al. Respiratory allergies: Salicaceae sensitization (Review). Exp Ther Med. 2021;21(6):609.
- McInnes RN, Hemming D, Burgess P, Lyndsay D, Osborne NJ, Skjøth CA, et al. Mapping allergenic pollen vegetation in UK to study environmental exposure and human health. Science of The Total Environment. 2017;599-600:483-99.
- CABI. Salix (Willows) Wallingford, UK2021 [cited 2021 18.11.21]. Available from: https://www.cabi.org/isc/datasheet/48455.
- Mansouritorghabeh H, Jabbari-Azad F, Sankian M, Varasteh A, Farid-Hosseini R. The Most Common Allergenic Tree Pollen Grains in the Middle East: A Narrative Review. Iran J Med Sci. 2019;44(2):87-98.
- Wong V, Wilson NW, Peele K, Hogan MB. Early Pollen Sensitization in Children Is Dependent upon Regional Aeroallergen Exposure. J Allergy (Cairo). 2012;2012:583765.
- Tawfeek N, Mahmoud MF, Hamdan DI, Sobeh M, Farrag N, Wink M, et al. Phytochemistry, Pharmacology and Medicinal Uses of Plants of the Genus Salix: An Updated Review. Front Pharmacol. 2021;12:593856.
- Oteros J, Pusch G, Weichenmeier I, Heimann U, Möller R, Röseler S, et al. Automatic and Online Pollen Monitoring. Int Arch Allergy Immunol. 2015;167(3):158-66.
- Yalcin AD, Basaran S, Bisgin A, Polat HH, Gorczynski RM. Pollen aero allergens and the climate in Mediterranean region and allergen sensitivity in allergic rhinoconjunctivitis and allergic asthma patients. Med Sci Monit. 2013;19:102-10.