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

Since 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.