Physiological change under OsHV-1 contamination in Pacific oyster Crassostrea gigas through massive mortality events on fields

Massive mortalities have been observed in France since 2008 on spat and juvenile Pacific oysters, Crassostrea gigas. A herpes virus called OsHV-1, easily detectable by PCR, has been implicated in the mortalities as demonstrated by the results of numerous field studies linking mortality with OsHV-1 prevalence. Moreover, experimental infections using viral particles have documented the pathogenicity of OsHV-1. The physiological responses of host to pathogen are not well known. In this study, a number of genes involved in the response to viral challenge have been identified and can be considered as confirmation of the role of the virus in the observed mortality. The aim of this study was to understand mechanisms brought into play against the virus during infection in the field. A microarray assay has been developed for a major part of the oyster genome and used for studying the host transcriptome. Spat with and without detectable OsHV-1 infection were compared by microarray during mortality episodes. The result allowed establishment of a hypothetic scheme of the host cell’s infection by, and response to, the pathogen. This response seems to be different to “sensu stricto” innate immunity through genic regulation of the virus life cycle. . Some regulatory response against the virus may explain that some oysters are able to survive infection by regulation of the viral genes associated with the OsHV-1 life cycle.