DAO 42:173-183 (2000)  -  doi:10.3354/dao042173

Concomitant herpes-like virus infections in hatchery-reared larvae and nursery-cultured spat Crassostrea gigas and Ostrea edulis

Tristan Renault*, Rose-Marie Le Deuff, Bruno Chollet, Nathalie Cochennec, André Gérard

Institut Français de Recherche pour l┬╣Exploitation de la Mer, Laboratoire de Génétique et Pathologie, BP 133, 17390 La Tremblade, France

ABSTRACT: Concomitant sporadic high mortalities were reported in France in May 1994 among batches of hatchery-reared larval Pacific oysters Crassostrea gigas and European flat oysters Ostrea edulis in 2 hatcheries, and in June and July 1994 among batches of cultured spat of both species in a shellfish nursery. Histological observation showed the presence of cellular abnormalities in moribund animals. Transmission electron microscopy revealed the presence of herpes-like virus particles in infected larvae and spat of both oyster species. This is the first description of a herpes-like virus infection in larval O. edulis. Viruses observed in diseased larvae and spat of both species are similar with respect to ultrastructure and morphogenesis. They were detected simultaneously in C. gigas and O. edulis larvae and spat, indicating possible interspecific transmission. Moreover, these viruses are associated with high mortality rates in both oyster species. An electron microscopic examination revealed hemocytes with condensed chromatin and extensive perinuclear fragmentation of chromatin. These data suggest that herpes-like viruses infecting oysters may induce apoptosis in oyster hemocytes.

KEY WORDS: Herpes-like virus · European flat oyster · Ostrea edulis · Pacific oyster · Crassostrea gigas · Oyster mortality · Concomitant infection · Virus replication · Apoptosis

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