Identification of a newly described OsHV-1 µvar from the North Adriatic Sea (Italy).

Surveillance activities of abnormal bivalve mortality events in Italy include the diagnosis of OsHV-1 in symptomatic oysters. OsHV-1-positive oysters (Magallana gigas) were used as source for in vivo virus propagation and a derived virus-rich sample was selected to perform a shotgun sequencing based on Illumina technology. Starting from this unpurified supernatant sample from gills and mantle, we generated 3.5 million reads (2 x 300 bp) and de novo assembled the whole genome of an Italian OsHV-1 microvariant (OsHV-1-PT). The OsHV-1-PT genome encodes 125 putative ORFs, seven of which had never been previously predicted in other sequenced Malacoherpesviridae. Overall, OsHV-1-PT displays typical features of microvariant OsHV-1 genomes while few polymorphisms (0.08%) determine its uniqueness. As little is known about genetic determinants of OsHV-1 virulence, the comparison of complete OsHV-1 genomes support a better understanding of the virus pathogenicity and provide new insights into virus-host interactions.