Bring out the tissues and antihistamines: like every year at the same time, ambrosia is back, to the chagrin of allergy sufferers and asthmatics. THE National Aerobiological Monitoring Network (RNSA) placed thirteen departments at “high level” allergic risk in its latest bulletin published on August 25. “Drôme, Isère, Ardèche, Rhône, Ain, Saône-et-Loire, Nièvre, Allier, Cher, Indre, Creuse, Vaucluse and Gard” are affected by this alert.
A late and severe pollinosis
“Ambrosia comes into pollination late in the season, explains Dr. Sophie Silcret-Grieu, allergist in Paris. First there is the tree pollen season in March-April, then the grass pollen season in June-July-August. Ambrosia pollens arrive at the end of summer, from mid-August to mid-September”. And as with other pollinosis, or pollen allergies, “ragweed triggers symptoms such as rhinitis, runny nose, sneezing, stuffy nose, scratchy throat, itchy eyes and asthma attacks in susceptible individuals. Classic symptoms, but which are often even more severe and violent with ambrosia”.
People allergic to ragweed can also suffer from “conjunctivitis and have swollen eyelids. A symptomatology that is expressed more aggressively than with other pollens, abounds Isabella Annesi-Maesano, director of research at Inserm, epidemiologist of allergic and respiratory diseases. Allergic reactions so severe that you can bleed when you blow your nose as the mucous membranes are inflamed”. Eczema-like skin reactions are also frequently observed. If you are allergic to it, “you have to consult, remember to watch the pollen alerts and follow your treatment well, especially if you are asthmatic, insists Dr. Silcret-Grieu. On the one hand, there are symptomatic treatments, to be taken as soon as the pollen arrives and as long as you have symptoms. But also desensitization treatments, to start upstream”.
Because with the late arrival of ambrosia, it’s a bit as if the pollen season was saving the worst for the end. “For people allergic to several varieties of pollen including ragweed, the fact of having had the first manifestations in early spring and summer makes the mucous membranes more vulnerable, more permeable to pollen, which can aggravate the symptoms of ragweed allergy, describes the allergist. There is then a doubly irritating action of ambrosia on the airways”.
A deleterious cocktail effect
To make matters worse, “pollution and global warming multiply the effect of pollen”, underline Dr. Silcret-Grieu and Isabella Annesi-Maesano together. “Pollution has two effects: it breaks the outer membrane of the pollen, which opens and releases its particles into the ambient air, explains the researcher. In addition, it increases the irritation of the airways: if you inhale a pollutant, it generates inflammation. Pollens and viruses can then penetrate more easily. The pollen-pollution cocktail effect is particularly deleterious”. Especially since “pollutants can attach themselves to pollen, which then acts as a vector in the respiratory tract,” adds Dr. Silcret-Grieu.
Global warming, as we have said, also plays its part. “Studies show that CO2 – a greenhouse gas – can increase the production of pollen in the plant, adds Isabella Annesi-Maesano. We can clearly see this this year, when we broke heat records, this has an effect on the plants, and the levels of pollen emitted”.
And “in the case of ambrosia, we have the very clear impression that global warming is causing the plant to rise in regions that were previously unaffected: it is proliferating and colonizing the territory”a.
An invasive and tenacious plant
In Auvergne-Rhône-Alpes, the massive arrival of ragweed pollen took place on August 11. There, the Regional Health Agency (ARS) implemented action plans in the 2000s to fight against this invasive and tenacious plant. The region – in particular the Rhone Valley – is the most affected in the country with 80% of reports, explains Frédéric Caray, in charge of the Auvergne-Loire ambrosia control plan for the Fredonnational surveillance network for species harmful to human health.
“It is a plant that has spread through road works and has a great ability to establish itself in field crops. The east of Lyon brought together all the conditions that facilitated its installation”, recalls Hervé Bertrand, environmental health technician at ARS Auverne-Rhône-Alpes and regional referent on ragweed. Other departments called “front areas”, less infested, are closely monitored such as Haute-Loire, Cantal, Charentes or Côte d’Or.
“The plant is intelligent and adapts to survive and spread out,” observes Isabella Annesi-Maesano. From now on, “we see ambrosia north of the Loire, notes Dr. Silcret-Grieu. Some patients in the Paris region have told me that they have observed it even though it is not an area that is supposed to be affected”.
A plant that is difficult to eradicate
Ambrosia has become a major and expensive public health problem: between 59 and 186 million euros per year. “It is considered a biological pollutant because it is a public health problem in the affected regions, underlines Dr. Silcret-Grieu. It is a weed, like most allergenic plants, which tends to proliferate in uncultivated land, which it is advisable to clear. There are campaigns against ambrosia, to prevent its proliferation, but it is very difficult to eradicate it”.
“You have to pull it out manually, cut it before it starts flowering to avoid the emission of pollen and its spread”, recommend the researcher and the allergist. Uprooting campaigns are organized in the spring until the end of July. A reporting platform has been set up and prefectural decrees make its destruction mandatory.
“If you see it, you have to pull it out immediately”
“If you see it in your garden, you have to pull it out immediately,” advises Isabella Annesi-Maesano. “It’s a struggle that interests everyone: communities, businesses and individuals,” adds Hervé Bertrand. On average, 10% of the population is allergic to ragweed in infested areas, but this percentage can reach more than 25%, he continues. And the number of allergic people could still grow with the increase in CO2 in the atmosphere, up to 10 million in 2041-2060, according to scientists.
For the time being, “only the arrival of the rain will bring some respite to allergy sufferers by placing the pollen on the ground, specifies Dr. Silcret-Grieu. But a short-lived respite, since after having benefited from the rain, the plants will pollinate even more strongly when the good weather returns”.