Herpes‐like virus infections in hatchery‐reared bivalve larvae in Europe: specific viral DNA detection by PCR

Periodic losses in oyster hatcheries are regularly reported in Europe. Herpes‐like virus infections seem to play a key role. Polymerase chain reaction (PCR) was used to investigate the presence of herpes‐like virus DNA in larval samples belonging to different bivalve species from different geographical origins. Seventeen samples of the 81 analysed appeared positive for the herpes‐like virus DNA by PCR. These results confirm previous data indicating that herpes‐like virus infections occur in commercial French hatcheries. Polymerase chain reaction positive results were also obtained for bivalve larval samples originating from Spain and the UK. The number of virus DNA positive samples depended on the primer pair used. The primer pair C2/C6 appears well adapted for herpes‐like virus DNA detection because of processing ease and great sensitivity. Positive samples were observed in four bivalve species: Crassostrea gigas, Ostrea edulis, Ruditapes decussatus and Ruditapes philippinarum. Herpes‐like virus DNA detection is reported in larval R. decussatus for the first time. Many samples in which viral DNA was detected by PCR correspond to larval batches presenting mortalities. Herpes‐like viruses may be one of the causative agents of mortalities observed in bivalve hatcheries.