IgE-mediated reactions
Intense hay fever, but not asthma, has been described. (6, 7) Although only very few reports document sensitisation to pollen from this tree, anecdotal evidence from areas where the tree is commonly found suggests that allergic sensitisation is common following exposure to the pollen. Furthermore, because of the close family relationship with white elm tree, which induces asthma, allergic rhinitis and allergic conjunctivitis, (8,9) clinical inferences may be drawn. (See White elm t8.)
In a Canadian study that evaluated the impact of different trees on asthma, along with the association between daily hospitalisations for asthma and daily concentrations of different tree pollens in 10 large Canadian cities, it was reported that for an interquartile increase in daily tree pollen concentration, the percentage increase in daily hospitalisation for asthma was 2.63% for Ulmus. (10)
Aerobiology studies often do not draw distinctions between the various species of Ulmus, but this may not be problematic; considering the close relationship between species of elm, cross-sensitisation or cross-reactivity to Ulmus is possible, and hence inferences can be drawn, including that individuals sensitised to cedar elm may be affected in areas where white elm or other members of the genus produce pollen.
In Tampa, Florida, in the USA, where the major tree-pollen season occurs from December until May, with a minor season occurring from October to November, elm tree pollen is important during the minor season. (11)
In Cordoba, Spain, aerobiology studies have reported pollen grains from the closely related species Ulmus minor in the air. (12) In Siena, in central Italy, elm tree pollen was found to be an important aeroallergen in March, but not during the rest of the tree-pollen season, (13) whereas in Modena, in northern Italy, the elm family contributed little pollen to the air (about 1% of the total recorded). (9)
In aerobiology studies of 9 districts of northern China, the most common aeroallergens in spring were often Ulmus, Populus and Salix. (1) Elm has also been reported to be an important tree pollen in Tehran, Iran. (15)
Pollen concentrations in the atmosphere of Lublin (eastern Poland) were reported to be the highest for Betula, Pinaceae and Alnus; and the lowest for Ulmus, Fagus and Corylus. Significantly, total pollen grains for Ulmus varied almost twofold between successive years. (16) Pollen from the Ulmus species has been reported to be an important allergen in Zagreb, Poland. (17)