Asthma sufferers in Geneva are bracing themselves for a difficult summer, as a result of an invasion by the dangerously allergenic ragweed.
Ragweed, also known by its Latin name, ambrosia artemisiifolia, is a native of North America. This invasive plant has already colonised the whole of Canada, while the US federal government and a number of states list it as a "noxious weed".
And with good reason. This annual plant, with its spikes of greenish bell-like flowers, is not as inoffensive as it looks. Its fine yellow grains of pollen are one of the main causes of late-season hay fever-type allergies in those places where it has a foothold.
This ambrosia is certainly not a food of the gods.
"The problem with ragweed is that its pollen is not only allergenic, it's also a powerful irritant, so it can induce a range of often severe symptoms in non-specifically allergic patients," says Pierre Gumowski, head of the allergy department of Geneva's Hôpital de la Tour.
Those symptoms, which include irritation to the eyes and skin and breathing difficulties, are difficult to treat and often lead to serious asthma attacks, even in those who have shown no previous susceptibility.
The danger period is late summer, when pollination takes place. With 20 per cent of the population asthmatic, the potential for a public health crisis is apparent.
"We've been sounding the alarm. It's important to get rid of it as quickly as possible," Gumowski told swissinfo. "If we let it grow, there will be a sharp increase in asthmatic patients being hospitalised. That's what we want to avoid."
Ragweed has been noticed sporadically in the canton for many years, in the course of regular surveys by Geneva's botanical gardens. This led to the creation of a special group, known as Ambrosia-Genève - comprising botanists, agronomists, meteorologists and doctors like Pierre Gumowski - which had the task of monitoring the situation and devising ways to control this unwanted visitor.
The increase in its incidence in the past couple of years - proven by scientific studies of soil and air contamination - has been dramatic.
France has been battling to contain it in the Rhone Valley for years, while Italy's Po Valley, the whole of Hungary, parts of Austria and southern Germany have been infested with it. Other Swiss cantons - notably Basel and Ticino - have begun being colonised.
A French programme to contain ambrosia had considerable success in reducing the number of cases caused by its pollen. But since the programme was stopped for financial reasons, there has been an explosion in the number of plants and the number of patients presenting symptoms.
Although Ragweed will thrive in gardens, building sites and along roadsides, it is particularly fond of fields of sunflowers. It is no surprise to learn, then, that it may have entered Europe in consignments of sunflower seeds or bird food.
As well as the serious health implications, ambrosia can have a serious impact on agriculture. The cost of ambrosia to the economy of Quebec alone has been estimated at almost SFr 50 million.
This weed reduces productivity by competing with crops. It also contaminates them, meaning they cannot be sold. In addition, ragweed is resistant to many kinds of herbicide. Several of those that are effective are banned in Switzerland.
The Ambrosia-Genève group wants to see those restrictions eased. It also wants farmers to be made more aware of the dangers and educated in how to treat their fields before sowing their crops.
"We have to do this preventive work before it becomes a major problem," Gumowski says.
by Roy Probert