Herpèsvirus infectant les bivalves marins : détection, génome et transmission

Since 1991, high mortality rates of larvae and juveniles of different bivalve mollusc species associated with herpesvirus infections have been reported in different countries. The aim of this study was to determine if more than one helpesvirus species was responsible for these infections or just one species exhibiting polymorphism. The investigations concentrated on the analysis of the virus genome, studies of virus transmission in different mollusc species and on the potential role of bivalve adults in the occurrence of infections. The analysis of various target sequences within the virus genome present in infected larvae samples demonstrated the presence of polymorphism. More notably a variant of the virus was identified and the variation appears independent of the host species and the geographic origin of the animais. Interspecies transmission assays demonstrated that the herpesvirus is not species specific within the range of mollusc species tested and suggests that unlike veliebrate herpesviruses, the bivalve herpesvirus has a wide host range. Intensive rearing could also promote the selection of new variants that are capable of crossing the species barrier and further broadening the host range. The detection of viral DNA and proteins in asymptomatic adult oysters demonstrate the ability of the virus to persist in its host and to be expressed as a chronic attenuated or asymptomatic infection, similar to other members of the family Herpesviridae. Adult bivalves would then represent a reservoir of infectious virus that may be transmitted, by the horizontal route to their larvae.