Influence of temperature on disease transmission associated with ostreid herpes virus OSHV-1 µVAR in relation to survival of juvenile Crassostrea gigas

• Main Authors: Petton, Bruno, Pernet, Fabrice, Robert, Rene, Boudry, Pierre, Alunno-bruscia, Marianne
• Format: Conference Object
• Language: English
• Published: Aquaculture Europe 13 "Making Sense of Science", 9-12 August 2013, Trondheim (Norway) 2013
• Subjects: Crassostrea gigas
• Online Access: https://archimer.ifremer.fr/doc/00151/26259/24343.pdf; https://archimer.ifremer.fr/doc/00151/26259/

Since 2008, mass mortalities of 1-yr-old oysters Crassostrea gigas associated with ostreid herpes virus OsHV-1 μVar have occurred along all coasts of France. These mortality events represent the most serious crisis for the French oyster industry since the introduction of C. gigas in the early 1970s. Temperature is commonly one of the major triggering factors of disease epizootics, notably for aquatic species. In France, OsHV-1 is generally detected in dying oysters when seawater temperature is higher than 16° C. The influence of temperature on OsHV-1 detection and expression was also demonstrated for C. gigas larvae and suspected for juveniles. The present study aims to characterize the effect of temperature on disease transmission and survival related with ostreid herpesvirus OsHV-1 µVar in juvenile C. gigas. To examine the effect of seawater temperature on disease transmission and related mortality of oysters, we conducted two sets infection experiments based on a unique biological material, i.e. healthy naive oysters that are free of mortality and negative for OsHV-1 µVar and Vibrio bacteria, which cohabitated with oysters previously exposed (challenged) to natural field conditions in areas where mortalities were occurring. The first set of experiments was carried out at 13.0° C and 20.6° C to investigate whether survival of healthy naive oysters was influenced by cohabitation with presumably infected (challenged) oysters, i.e. that were exposed to field conditions with surrounding mortalities. The second set of experiments aimed to investigate whether disease transmission and related survival of oysters were influenced by seawater temperature. Challenged oysters were placed in contact with naive oysters at 8 temperatures ranging from 13.4° C to 29.0° C. Animals were regularly sampled for OsHV-1 DNA detection by real-time qPCR and for quantification of Vibrio bacteria on CHROMagar media. The optimal temperature range for disease transmission from challenged (field-exposed) to unexposed (naive) cohabiting animals was between 16.2° C and 21.9° C, which corroborated field observations (Pernet et al. 2012). Our results suggested that a long-term period (40 days) at low temperature (13° C) may offer a way to stop or mitigate mortalities in oysters that have been exposed to an infecting environment.