A novel divergent group of Ostreid herpesvirus 1 μVar variants associated with a mortality event in Pacific oyster spat in Normandy (France) in 2016

• Published in: Journal of Fish Diseases
• Main Authors: Burioli, Erika A. V., Varello, Katia, Lavazza, Antonio, Bozzetta, Elena, Prearo, Marino, Houssin, Maryline
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: Pacific; Pacific oyster
• Online Access: http://dx.doi.org/10.1111/jfd.12883; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjfd.12883; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfd.12883

Abstract The acute course of disease in young oysters infected by Os HV ‐1 and the rapid tissue degradation often preclude histological examination of specimens collected during outbreaks in field. Herein, live spat originated from two geographical areas were sampled just at the onset of a mortality event that occurred in Normandy (France) in June 2016. The lesions, associated with high Os HV ‐1 DNA quantities, were characterized by severe and diffuse haemocytosis mainly involving blast‐like cells, myocyte degeneration and large, irregularly shaped degenerate eosinophilic cells in the connective tissue. The herpesvirus was identified by negative staining TEM and real‐time PCR . Sequencing of the C region and ORF s 42/43 confirmed that the variants met the definition of Os HV ‐1 μVar. We sequenced 30 other ORF s in twenty Os HV ‐1‐positive individuals and compared them to the μVar specimens isolated between 2009 and 2011. The ORF s encoding putative membrane proteins showed the highest number of variations. Seven different genotypes were identified, confirming the presence of relevant genetic diversity. Phylogenetic analysis provided evidence for a well‐separated μVar new group, with an evolutionary divergence estimated at 0.0013 from the other μVar variants. The geographical distribution of these newly described variants and their effective virulence should be investigated in future.