L’ambroisie à feuilles d’armoise : une menace croissante pour la santé et l’environnement

Rhinitis, conjunctivitis, and even asthma attacks… The Ambrosia artemisiifolia, or common ragweed pollen – which typically peaks in mid-August – is highly allergenic and often causes acute symptoms. According to the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), currently 3% of the French population is sensitized to it. However, it is the projections for the number of allergics by 2050 that are alarming: according to some scientific studies, up to 15% of the French population could become sensitized! Originally from North America, Ambrosia is an invasive plant in our country. It was accidentally introduced to France in the mid-19th century, imported from the United States along with violet clover seeds. How can such a rapid increase occur in just a few decades? Is air pollution involved? What role will climate change play? Will the increase in atmospheric carbon dioxide (CO2) concentration have an impact? And most importantly, how can we fight against this progression? Harder to manage allergies Coughing, blocked and runny nose, itching… Ambrosia allergy causes more severe and harder to manage symptoms than other pollen allergies, according to healthcare professionals. In France, the ambrosia pollen season lasts nearly two months, making it one of the longest. The consequences of allergies can be particularly debilitating, significantly affecting the quality of life of those affected. Historically, the main areas of ambrosia establishment were the Rhône and Loire valleys. But since 2005, an acceleration of expansion has been observed in other regions: Nouvelle-Aquitaine, Occitanie, Northern Provence-Alpes-Côte d’Azur, Centre-Val de Loire (FREDON). This expansion occurs naturally through seed dispersal, which can be facilitated by agricultural activities. However, to explain the future spread of ambrosia in France, other factors must be considered. Air pollution, suspect but not guilty? Air pollution is the first potential culprit that comes to mind when it comes to allergies. However, in the case of ambrosia, it is probably not the cause. Although atmospheric pollutants do have a proven effect on worsening symptoms severity. The ambrosia pollination period sometimes coincides with peaks of ozone or fine particle pollution (particularly from forest fires). Atmospheric pollutants are indeed responsible for both respiratory irritation and direct alteration of pollen. These two phenomena can lead to exacerbation of inflammation and respiratory allergy symptoms. Ambrosia pollen grains can cause severe allergies. However, the role that air pollution could play in sensitization, in other words, the possibility of developing symptoms, has not yet been formally demonstrated. Beyond pollution, the roles of the increase in atmospheric CO2 concentration and climate change are among the main suspects. The impact of increased CO2 concentration Atmospheric carbon dioxide concentration has been increasing since the 19th century: it has gone from 0.028% in 1850 to 0.042% today. By the end of the century, it is expected to reach between 0.06% and 0.1%, depending on decarbonization efforts produced in our societies. When atmospheric CO2 concentration increases, photosynthesis also increases, meaning plant growth is more substantial. However, it should be noted that plant growth is also influenced by other parameters such as temperature and drought episodes, and all plants do not respond to these changes in the same way. Nevertheless, the impact of this increase in atmospheric CO2 on plant growth and reproduction is already visible in some species. What about ambrosia? To find out, scientists use greenhouses to simulate conditions corresponding to future atmospheres and try to predict their effects on pollen production. Ambrosia plants are cultivated under either current atmospheric conditions (0.042% CO2) or under elevated CO2 concentrations (e.g., 0.06% CO2). Let’s be warned right away: the projections are not good… More allergenic ambrosia pollen, in greater quantity These experiments indicate that the increase in atmospheric CO2 will most likely lead us to breathe a greater quantity of ambrosia pollen in the future. Indeed, various studies have shown a 1.5 to 3-fold increase in pollen production due to elevated atmospheric CO2. Research has also revealed faster ambrosia growth and an extended pollination period. Furthermore, it has been found that ambrosia crops grown under enriched CO2 atmospheres produce more pollen. Worse yet, under these conditions, the released pollen contains increased quantities of allergens (the proteins responsible for allergies). Recent studies have confirmed that pollen from plants exposed to elevated CO2 levels is more allergenic. As a result, it is feared that in the future, the levels of allergens we will come into contact with will be higher, and allergic symptoms will be exacerbated. The role of climate change Carbon dioxide will have a direct effect on ambrosia growth and the quantity and quality of its pollen. It will also have an indirect effect on its pollination by inducing climate change (along with other greenhouse gases). Warmer temperatures, in fact, favor pollen production. In 2022, the amounts of ambrosia pollen detected in Nouvelle-Aquitaine, on pollen sensors located in Mareuil and Angoulême, have never been higher. A positive correlation has been established between the amount of pollen in the air and the number of sick individuals. In other words, greater pollen production means more people allergic to this pollen. Ambrosia could benefit from climate change. Climate change could also lengthen the pollen season, increasing the duration of allergic symptoms in affected individuals. However, this season lengthening effect is not sufficiently documented at present to have certainty about this trend in the decades to come. One thing is certain: the future climate will be more conducive to the spread of ambrosia. A larger number of French regions will become infested with this invasive plant, and a larger population will therefore be exposed to its pollen. As a consequence, once again, there will be an increased likelihood of pollen sensitization, as well as an increase in the number of allergic individuals. How many additional allergic individuals? Modeling studies have recently estimated the evolution of ambrosia allergy in France in the coming decades. The geographical expansion of ambrosia in France by 2041-2060 has been calculated, taking into account both the influence of climate change and the increase in atmospheric CO2 concentration. In summary, the increase in ambrosia allergies will directly depend on the extent of global CO2 emissions reduction. The higher our emissions, the higher the number of allergies will be… Beyond the atmospheric CO2 level, the spread of ambrosia will also depend on the rate of plant spreading and therefore on the means allocated to curb it. For France, the prevalence of ambrosia allergies is at risk of increasing from 3% currently to over 15% in 2050, representing more than 10 million people… To avoid reaching this point, resistance to ambrosia is being organized. Several structures or associations are already fighting against this plant with the support of public authorities. The National Aerobiological Surveillance Network (RNSA) measures the quantities of pollen grains present in the air. These analyses allow real-time monitoring of areas affected by ambrosia and provide information to healthcare professionals and allergic individuals who can subscribe to
#millions #Français #allergiques
2023-08-07 23:09:45