Variants of herpetic virus ostreid herpesvirus-1 (OsHV-1) in young Pacific oyster Crassostrea gigas.

International audienceSince the 1990s, high mortality rates of young Pacific oysters Crassostrea gigas have been regularly recorded in France and affect mainly spat (oysters less than 1 year old). Pathogens infecting marine bivalve mollusks have been studied particularly due to their economic and ecologic impacts on the farmed and wild oysters. A herpes virus belonging to the family Malacoherpesviridae and called Ostreid Herpesvirus-1 (OsHV-1) has been detected in infected oysters. Since the summer 2008, the mortality of spat has greatly increased on the French coast (with a mortality rate ranging from 40 to 80%) and may be linked to a variant of the OsHV-1, named OsHV-1 μVar. Few variants of the OsHV-1 and genotypes closed to the OsHV-1 μVar have been described in several areas in the world. However, the OsHV-1 μVar is predominant in analyzed samples and the reference genotype of the OsHV-1 has not been detected since 2008. The causes of the emergence of the OsHV-1 μVar and its rapid spreading in the world are currently unknown