Experimental infection of European flat oyster Ostrea edulis with ostreid herpesvirus 1 microvar (OsHV-1 μvar): Mortality, viral load and detection of viral transcripts by in situ hybridization

Ostreid herpesvirus 1 (OsHV-1) infections have been reported in several bivalve species. Mortality of Pacific oyster Crassostrea gigas spat has increased considerably in Europe since 2008 linked to the spread of a variant of OsHV-1 called var. In the present study we demonstrated that O. edulis juveniles can be infected by OsHV-1 mu var when administered as an intramuscular injection. Mortality in the oysters injected with OsHV-1 mu var was first detected 4 days after injection and reached 25% mortality at day 10. Moreover, the high viral load observed and the detection of viral transcripts by in situ hybridization in several tissues of dying oysters suggested that OsHV-1 mu var was the cause of mortality in the O. edulis juveniles. This is therefore the first study to provide evidence about the pathogenicity of OsHV-1 var in a species that does not belong to the Crassostrea genus. Additionally, we present a novel method to detect OsHV-1 transcripts in infected individuals' using in situ hybridization. (C) 2016 Elsevier B.V. All rights reserved.