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

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.