title: Crassostrea gigas mortality in France: the usual suspect, a herpes virus, may not be the killer in this polymicrobial opportunistic disease.
abstract: Successive disease outbreaks in oyster (Crassostrea gigas) beds in France have resulted in dramatic losses in production, and subsequent decline in the oyster-farming industry. Deaths of juvenile oysters have been associated with the presence of a herpes virus (OsHV-1 μvar) and bacterial populations of the genus Vibrio. Although the pathogenicity of OsHV-1 μvar, as well as several strains of Vibrio has been demonstrated by experimental infections, our understanding of the complexity of infections occurring in the natural environment remains limited. In the present study, we use specific-pathogen-free (SPF) oysters infected in an estuarine environment to study the diversity and dynamics of cultured microbial populations during disease expression. We observe that rapid Vibrio colonization followed by viral replication precedes oyster death. No correlation was found between the vibrio concentration and viral load in co-infected animals. We show that the quantity of viral DNA is a predictor of mortality, however, in the absence of bacteria, a high load of herpes virus is not sufficient to induce the full expression of the disease. In addition, we demonstrate that juvenile mortalities can occur in the absence of herpes virus, indicating that the herpes virus appears neither essential nor sufficient to cause juvenile deaths; whereas bacteria are necessary for the disease. Finally, we demonstrate that oysters are a reservoir of putative pathogens, and that the geographic origin, age, and cultivation method of oysters influence disease expression.
authors.affiliation: LEMAR UMR 6539, Ifremer Argenton-en-Landunvez, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Petton
authors.affiliation: Unité Physiologie Fonctionnelle des Organismes Marins, Ifremer Plouzané, France ; CNRS, Equipe Génomique des Vibrios, LBI2M, UPMC Paris 06, UMR 8227, Integrative Biology of Marine Models, Sorbonne Universités Roscoff, France.
authors.forename: Maxime
authors.initials: M
authors.lastname: Bruto
authors.affiliation: Unité Physiologie Fonctionnelle des Organismes Marins, Ifremer Plouzané, France ; CNRS, Equipe Génomique des Vibrios, LBI2M, UPMC Paris 06, UMR 8227, Integrative Biology of Marine Models, Sorbonne Universités Roscoff, France.
authors.forename: Adèle
authors.initials: A
authors.lastname: James
authors.affiliation: Unité Physiologie Fonctionnelle des Organismes Marins, Ifremer Plouzané, France ; CNRS, Equipe Génomique des Vibrios, LBI2M, UPMC Paris 06, UMR 8227, Integrative Biology of Marine Models, Sorbonne Universités Roscoff, France.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Labreuche
authors.affiliation: LEMAR UMR 6539, Ifremer Argenton-en-Landunvez, France.
authors.forename: Marianne
authors.initials: M
authors.lastname: Alunno-Bruscia
authors.affiliation: Unité Physiologie Fonctionnelle des Organismes Marins, Ifremer Plouzané, France ; CNRS, Equipe Génomique des Vibrios, LBI2M, UPMC Paris 06, UMR 8227, Integrative Biology of Marine Models, Sorbonne Universités Roscoff, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Le Roux
keywords: experimental infection; herpes virus; pacific oysters; summer mortality; vibrio pathogenicity