Its red stems and spike-like flowers grow at high speed, in the form of an invasive bush. Once established, ragweed is highly allergenic. It irritates the eyes, makes the nose run and can even cause asthma. Unlike hay fever caused by grass in the spring, it is in August that the plant rages.
While the number of people with allergies could increase with global warming, monitoring its spread has become a goal of health organizations. At the moment, the National Agency for Health, Food, Environment and Labor Safety (Consider) estimates that 3% of the population knows this.
“Ambrosia has been present for many years in Auvergne-Rhône-Alpes, and we have the impression that its presence will grow in Lyon, Grenoble, and Valence”, list Frédéric de Blay, president of the French Allergy Federation. Almost 80% of reports in France come from the region.
Although the plant, native to North America and accidentally imported to France in 1860, is well known, eradicating it remains a challenge for the authorities. “Ambrosia develops, for example, when the soil turns on a construction site, in a region where it is installed. Once it starts, it’s hard to stop it”admitted the allergist.
Health organizations remain vigilant
In Auvergne-Rhône-Alpes, the Regional Health Agency (ARS) renewed a prevention system. During work in the region, they planted grass, for example, to prevent ragweed from taking root and, in five years, more than 6,000 people learned how to recognize it, in order to better eliminate it.
The National Aerobiological Monitoring Network (RNSA), in partnership with the Federation of Approved Air Quality Monitoring Associations (Atmo) also publishes, every week, a bulletin which informs about the risks of allergies in each department.
It remains nonetheless complex to anticipate the exact consequences of global warming on the spread of ragweed allergies, acknowledged the doctor. It could certainly multiply the cases of allergies to pollen, including those from ragweed and thus multiply the number of people affected, but “also has the opposite effect”, explains Frédéric de Blay. For the allergist at the University Hospital of Strasbourg, the flowers, in addition to being pollinated earlier, could also be faster burned by the sun. This would prevent the spread of the plant, as in Provence-Alpes-Côte d’Azur, where the plant is present.
How to identify the symptoms? Colds, asthma and watery eyes… only an allergist can diagnose sensitization after testing. But certain signs can alert: if the symptoms are similar to those caused by grass pollen, they are also more disabling. “Major asthma attack can be even alert”quoted by Frédéric de Blay.
The treatment is based on the prescription of antihistamines – the sale of which rose at the end of August in the metropolitan area of Lyon -, corticosteroids and inhalers in the event of asthma. But the president of the French federation of allergies insists: it is better to focus on prevention. “The best way to fight remains to know how to recognize the plant, and, if necessary, make it disappear. »