Gastronomes are in a cold sweat over warnings that they might be deprived of a cherished delicacy by a mystery disease that is devastating France's oyster population.

With farmers lamenting a sudden and inexplicable rise in the death rate of young oysters, an alarming shortage is looming. The problem is so grave that Michel Barnier, the Agriculture Minister, abandoned World Trade Organisation negotiations yesterday for an urgent visit to scientists and producers on the Atlantic Coast. He urged researchers to save next year's Christmas and new year meals in France with a cure for la surmortalité mystérieuse.

Several theories have been suggested to explain the phenomenon, including toxic algae and a rise in sea temperatures leading to an abnormally high quantity of the plankton eaten by oysters, which are dying of indigestion. But the most likely cause appears to be a combination of OHS-V1, a herpes-like virus, and the Vibrio splendidus bacterium. Both are constant menaces for oysters but are particularly fierce this year after a mild winter and a rainy spring.

Confédération Paysanne, the left-wing farming union, blamed industrialisation of oyster production, which it said had provided a breeding ground for viruses and bacteria.

France's 20,000 oyster farmers insist that gourmets can look forward to the coming festive season with confidence because the disease has had no effect on the three-year-old shellfish, which are ready to be eaten.

Indeed, they appear healthier and fleshier than ever, to the bewilderment of experts. But producers are reporting the loss of between 40 per cent and 100 per cent of one-year-old oysters in what is being described in the press as a national crisis. The mortality rate among two-year-old oysters is 15 per cent, compared with 8 per cent in an average year, according to the French Institute for Research into Use of the Sea.

This could have a big impact next year and in 2010, according to Le Parisien, which said that it would be difficult to supply demand. At best the upshot will be a price increase for a delicacy that costs between €9 (£7) for six huîtres fine de claires and €19.20 for half a dozen huitres spéciales in the Bar à Huîtres in Montparnasse, Paris.

At worst, it will signal an oyster-less period while stocks are replenished. Confédération Paysanne said that French production would be halved in 2010. The repercussions could be felt elsewhere since France is the world's fourth biggest oyster producer - and the biggest in Europe - with an annual supply in a normal year of 130,000 tonnes.

Britain's far smaller oyster industry appears to have escaped unscathed. “The whole thing is extremely odd,” Peter Hunt, director of the Shellfish Association of Great Britain, said. “Even the Channel Islands haven't got it. We don't quite know why.” Chefs and managers in London's restaurants appeared confident yesterday of maintaining their supply. Most buy oysters from Britain and Ireland.

Caio Souza, manager of the Oyster Bar at the Michellin-starred Bibendum restaurant, said: “We do have one French oyster on the menu, but that comes from a UK provider. Most of our oysters come from UK farms, so it shouldn't affect us.”

Pearls of wisdom

— France is Europe’s leading oyster producer, hauling in 130,000 tonnes a year from the Atlantic and Mediterranean. The French also are the biggest consumers, with an average of about 50 oysters per person a year

— The Romans popularised oysters in Britain. Large numbers of shells have been found at Roman sites

— From Roman to Victorian times, oysters occurred naturally in such large numbers that they were seen as a food for the poor. In Dickens’s The Pickwick Papers, Sam Weller remarks: “Oysters and poverty always seem to go together”

— The oyster farming industry in Britain is worth £23.5 million

Sources: Times Archive, agencies, the Shellfish Association of Great Britain

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