Scientists think that a warm winter and wet spring caused the young oysters to grow too fast by feeding on abundant plankton and this made them vulnerable to Oyster Herpes virus type 1.
Jacques Sourbier, regional president of the Loire's national shellfish producers' body, has been quoted by the AFP news agency as saying that the problem they are facing now is "every bit as worrying and serious as last year".
Oyster beds in the Mediterranean Sea and as far up the coast as Normandy have also been hit badly by the disease.
