Contribution of viral genomic diversity to oyster susceptibility to the Pacific oyster mortality syndrome
Pacific oyster juveniles are subjected to recurrent mass mortality episodes that constitute a threat for oyster industry. This mortality syndrome named "Pacific Oyster Mortality Syndrome" (POMS) is a polymicrobial disease but recent works have shown that the pathogenesis process is initiated by a primary infection by a variant of an Ostreid herpes virus, OsHV-1 µVar. The characterization of OsHV-1 genome during different disease outbreaks occurring in different geographic areas has revealed the existence of a genomic diversity for OsHV-1 µVar but the biological significance of this diversity is totally misunderstood. In order to go further in the understanding of the consequences of OsHV-1 diversity on POMS, we confronted 5 biparental families to 2 different infectious environments of the French coasts (Atlantic and Mediterranean). We observed that the susceptibility to POMS can be different among families within the same environment but also for the same family between the two environments. Viral diversity analysis revealed that Atlantic and Mediterranean POMS are caused by two distinct viral populations. Finally, we observed that oyster families are infected by distinct viral populations within a same infectious environment. Altogether these results suggest that the co-evolution processes playing between OsHV-1 µVar and oyster populations have selected a viral diversity that could facilitate the infection process and the transmission in oyster populations. These new data must be taken into account to develop adapted selection process in the future.