THERMAL CHALLENGE AS A SANITARY QUALIFICATION TEST OF OYSTER SPATS Crassostrea gigas AND OF THEIR ECOSYSTEMS WITH REGARD TO THE HERPESVIRUS OSHV-1 MVAR

摘要

Since 2008, mass mortalities of juvenile oysters Crassostrea gigas associated with ostreid herpevirus OsHV-1 uVar (Segarra et al. 2010) have occurred along all coasts of France when sea water temperature is higher than 16°C (Pernet etal. 2012). Laboratory experiments have established a direct link between the oyster mortalities and the infection by OsHV-1 uVar (Schikorski et al. 2011). OsFfV-1 DNA can be quantified and detected by quantitative polymerase chain reaction (qPCR) above a threshold of 102 copies mg'1 of wet tissues (Pepin et al. 2008). But this threshold does not allow to identify any asymptomatic individuals. In this context, we proposed a two-step methodological approach to qualify the sanitary status of C. gigas spats and of their ecosystems. The first step consisted in testing under laboratory conditions a thermal challenge based on a sharp increase in water temperature (>16°C) to test the sanitary status of C. gigas spats with regard to OsHV-1 uVar. In the second step, spats thatwere produced under a standardized laboratory protocol and that were qualified as naive after the thermal challenge with regard to OsHV-1 uVar (i.e. naive standardised spats, NSS) were deployed in the field (Brest Harbour) for a OsHV-1 uVar imprint. Then they were brought back to the laboratory for a 21°C thermal challenge to reveal the disease. The objective of this study was to determine the periods and the duration of OsHV-1 uVar infectivity in the ecosystem. The aim of this sanitary qualificationmethod was to provide an objective and accurate test to determine the status of oysters which can be used as a management tool of OsHV-1 uVar sanitary risk.