Potential pathogens associated with abnormal mortalities

In France abnormal mortalities of mollusks affect many species of bivalves. They occur mainly in summer and concern all the French coastline. For Crassostrea gigas, they affect all life's stages but more particularly spat. A pathology monitoring network, REPAMO, was created at the beginning of the nineties in France in order to answer European requirements as regards mollusk pathology. REPAMO observes whether there is abnormal mortality and keeps track of the health situation of mollusk stocks including the presence of pathogens notifiable to the European Union and OIE. When mortalities occur, the network REPAMO, samples the populations and performs different types of analysis (histology, bacteriology, viral detection) in order to detect potential pathogens. In France, different agents have been sometimes associated with abnormal mortalities of bivalves such as herpes-virus in Crassostrea gigas. Bacterial agents can be also involved. Indeed hemolymph of moribund oysters from open sea and from hatchery are often invaded by one Vibrio species belonging to V. splendidus group or V. aestuarianus. These observations suggest that Vibrio could induce or aggravate mortality in oysters weakened by environmental or physiological (maturation) factors.