Phylogenomic evidence for host specialization and genetic divergence in OsHV-1 infecting Magallana gigas and Ostrea edulis

Cross-species transmission is a major driver of disease emergence in humans and animals. The Ostreavirus ostreidmalaco1 (OsHV-1) is mainly associated with mortality in the Pacific oyster Magallana gigas , but has also been found in other mollusks, including the European flat oyster Ostrea edulis . This raises questions about OsHV-1 host specificity. This study explored the genetic differentiation of OsHV-1 in M. gigas and O. edulis and the underlying mechanisms. Using high-throughput sequencing, 40 OsHV-1 genomes were obtained from both O. edulis and M. gigas and were analyzed to assess viral diversity, lineage isolation, and cross-species transmission. Comparative genomics, population genetics, phylogenetic and phylodynamic methods revealed that host species significantly influence viral genetic structure. The data suggest that OsHV-1 was introduced in Europe with M. gigas , followed by a cross-species transmission event and divergence into two distinct lineages. Selection signals were identified in genomic regions involved in key viral functions, including host binding, DNA replication, and membrane-associated proteins, indicating possible adaptation to different hosts. Future research should investigate coevolution between OsHV-1 and a broader range of host species using phylogenetic approaches to better understand host-virus dynamics.