A herpes‐like virus infecting Crassostrea gigas and Ruditapes philippinarum larvae in France

Concomitant sporadic high mortalities were reported in June 1997 among batches of larval Pacific oyster, Crassostrea gigas, and Manila clam, Ruditapes philippinarum, in a French commercial hatchery. Histological observation showed the presence of cellular abnormalities in affected animals. Electron transmission microscopy revealed the presence of herpes‐like virus particles in infected larvae of both bivalve species. Viruses observed in C. gigas and R. philippinarum are closely related with respect to ultrastructure and morphogenesis. They were detected simultaneously in both bivalve species larvae indicating possible interspecific transmission. Moreover, PCR analysis using oyster herpes‐like virus specific primers allowed amplification of fragments of expected sizes for both bivalve species and demonstrated the presence of viral DNA. The PCR products obtained for both bivalve species and digested by restriction enzymes displayed the same patterns. These data suggest that the same herpes‐like virus may infect larval oysters and clams.