European ash
Summary
European ash trees (Fraxinus excelsior) are distributed across temperate regions of Europe, North America and central Asia. Fraxinus pollen is a potent allergen source causing asthma, allergic rhinoconjunctivitis and potentially urticaria and allergic dermatitis. Ash pollen shares structural and allergenic similarities with other members of the Oleaceae (olive) family, although there is conflicting evidence for cross-reactivity with olive tree pollen.
Route Of Exposure
Main
The main route of exposure is inhalation.
Clinical Relevance
European ash is a potent allergen source and a common cause of allergic rhinitis, conjunctivitis and asthma. The prevalence of ash pollen sensitization in Germany is about 10%, although it may be underestimated because the ash pollination season in Europe overlaps with birch (Betulaceae). In a study of 5416 Austrian patients sensitized to any pollen, 17.6% had a positive skin prick test to ash. In northern Iran, 36.7% of 1006 allergic patients showed a positive skin prick test to Fraxinus excelsior; this was significantly associated with asthma and allergic rhinitis, although urticaria and atopic dermatitis were also recorded. In a New York study, 27% of 371 allergic patients were sensitized to ash, while in Istanbul, 8.1% of 60 allergic patients showed a positive skin prick test to ash, which was the main sensitizer among the woody plants tested.
Allergic rhinitis
In a Belgian study comparing pollen exposure and sales of allergic rhinitis medication, positive associations were found between Fraxinus pollen counts and medication sales.
Other topics
In nasal provocation tests, 58% of 113 ash-sensitized patients showed symptoms of allergy, while 42% were clinically silent. 94% of sensitized patients and 88% of allergic patients were poly-sensitized to three or more allergens in addition to ash pollen, and 86% of all patients also had a positive skin prick test to birch (Betulaceae) pollen.
Diagnostics
Detection
Ash pollen is sampled using a vacuum air sampler such as the Burkard volumetric spore sampler or the Hirst-type pollen trap.
Testing ash sensitization using specific IgE to native ash extract is almost as effective as the skin prick test (SPT), with 98% of 113 SPT-positive patients showing specific IgE.
Prevention And Therapy
Allergen immunotherapy
One study suggests that better standardized or more widely available olive pollen extracts may be used instead of ash pollen extract for allergen-specific immunotherapy; this is not supported by a more recent study.
Prevention strategies
Avoidance
Allergenic vegetation maps may contribute to allergy risk assessments by showing the location of ash 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. Fraxinus allergy risk periods can also be forecasted using regression equations of pollen count, rainfall and temperature.
Cross-Reactivity
Extensive immunological cross-reactivity between olive, ash and privet pollen may lead to poly-sensitization of susceptible patients due to the priming effect. Cross-reactivity between the main allergens of Fraxinus and Olea species has been demonstrated by using Ole e 1 (olive) antibodies to detect Fra e 1 (ash) allergens in the atmosphere. One study found that determining specific IgE to Ole e 1 was as effective at diagnosing ash pollen allergy as determining IgE to Fra e 1, whereas another concluded that in countries where sensitization to ash does not occur via the olive tree, testing for component olive allergens (rOle e 1, nOle e 7, rOle e 9) will not reliably identify ash sensitization and allergy. There is very limited cross-reactivity between ash and birch pollen allergens.
References
- LOINC. European Ash wood dust IgE Ab [Units/volume] in Serum 2021 [cited 2021 16.11.21]. Available from: https://loinc.org/96280-3/.
- CABI. Fraxinus excelsior (ash) Wallingford, UK2021 [cited 2021 16.11.21]. Available from: https://www.cabi.org/isc/datasheet/24522.
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