Ambrosia artemisiifolia (ragweed) in Germany - current presence, allergological relevance and containment procedures

Abstract

Ambrosia artemisiifolia (ragweed) is a neophyte in Europe and Germany, which originated from the United States of America. In the USA the rate of sensitization against ragweed equals that of grass pollen, and without containment the rate of allergic sensitizations against ragweed pollen will clearly increase. Currently, the most frequent sensitizations in Germany are against grass pollen, followed by sensitizations against house dust mite and birch pollen. Ragweed pollen evokes symptoms at about 10 pollen/m3, grass pollen at about 15 pollen/m3. These concentrations of ragweed pollen are only reached on limited occasions in Germany. Ragweed cross-reacts with mugwort (Artemisia vulgaris) and a correct diagnosis is only feasible with the ragweed specific allergen Amb a 1. Due to cross reactivity with mugwort, new sensitizations against ragweed pollen are not needed to evoke allergic symptoms. The neophyte encounters an already mugwort-sensitized population, extends the pollen season and may provoke new sensitizations. Ragweed sensitizations are characterized by an increased tendency to also affect the lower airways, which is less with mugwort sensitizations. Thus containment of ragweed is needed. Ragweed seeds are imported or spread by contaminated bird feed, the transport of ragweed contaminated soil (also in tyre treads) and agricultural products from infested areas. States bordering on ragweed positive areas, like Brandenburg and Bavaria, are especially at risk and invasion is already underway. Ragweed seeds survive up to 40 years in soil, and so extended timescales for eradication and observations are needed. Germany is, compared to other countries like France (Rhone-Valley), Italy (Po-Valley), Ukraine and Hungary, limited in respect to ragweed infestation. Conditions in Germany are therefore favourable for the containment of ragweed. Switzerland implemented legislation against birdseed contamination by ragweed early during the plants expansion, and obligatory ragweed registration- and eradication showed that ragweed containment is possible. Without counter measures ragweed expansion in Germany will take place, resulting in more allergic disease. Considering the increasing number of allergic individuals, even without ragweed invasion, containment of the neophyte should be actively persued. Unfortunately, time is running out.

Keywords: Amb a 1; ambrosia; climate change; pollen; ragweed; sensitization.

Figures

Fig. 1

Spread of ragweed in Europe. Yearly modelled ragweed pollen emission (pollen/m2/year, a measure for plant presence) and modulated pollen concentration (pollen index, sum of daily concentrations) in Europe. Averaged 2005–2011. Courtesy of Prank et al. [1] © Prank et al. [1]

Fig. 2

Appearance of the plant. Morphology of Ambrosia artemisiifolia (ragweed) and the very similar Artemisia vulgaris (mugwort). Plant, seeds, microscopic image after safranin staining (red) and electron microscopic image of pollen of both species. Ambrosia seeds are 2–4 mm, Artemisia seeds are smaller. Both Asteraceae look similar but can be discriminated by the leaf bottom that is white with mugwort and similar green as the topside for ragweed. Aerobiologic and immunologic both pollen species are clearly different. © (8) Buters, J.

Fig. 3

Electron microscopic image of the liberation of ragweed pollen. Due to a mechanism, different from anthers of other pollen species, pollen of ragweed is pushed out of the anthers. a: anther during opening. b: empty anther. Source: Weichenmeier, I. / ZAUM © Weichenmeier, I. / ZAUM

Fig. 4

Ragweed populations in Germany. a: Reported ragweed populations > 100 plants during 2000–2010. Countries are colored red when at least one population was reported. b: The situation in 2014 [25]: the classification included size, number of individuals, persistence, expansion tendency and presence at roadsides. Source: own measurements, literature and unpublished data from third parties. © Alberternst, B. (11.07.2011)

Fig. 5

Ragweed pollen index (yearly sum of pollen/m3, average 2012–2014 of those stations with values from all years) of PID-stations. Pollen can be introduced by long-range transport and are no evidence of presence of ragweed plants in a certain area. Monitoring sites without ragweed pollen are not shown. Bars represent the amount of Ambrosia pollen. (max. 1,000 ragweed pollen/m3). For Berlin and Munich that have several stations only the highest numbers were depicted. © Albertsernst

Fig. 6

Extended population of ragweed in a sunflower field in Niederlausitz. Essential for Germany is the active detection of ragweed populations by botanists. Calls to the general public are useful but insufficient as the reports stem mostly from the direct environment of the observer and the number of reports correlated with journalist activities. After random sampling it was calculated from test areas in Bavaria [54] that the actual ragweed populations probably exceed the known population by two- to four-fold. Legal regulations for ragweed control are lacking in Germany. © Buters, J.