Salinity influences disease-induced mortality of the oyster Crassostrea gigas and infectivity of the ostreid herpesvirus 1 (OsHV-1)

M Fuhrmann,V Quillien,F Pernet,B Morga,B Petton,N Faury

doi:10.3354/aei00197

Abstract

Mortality of young Pacific oysters Crassostrea gigas associated with the ostreid herpesvirus 1 (OsHV-1) is occurring worldwide. Here, we examined for the first time the effect of salinity on OsHV-1 transmission and disease-related mortality of C. gigas, as well as salinity-related effects on the pathogen itself. To obtain donors for OsHV-1 transmission, we transferred laboratory-raised oysters to an estuary during a disease outbreak and then back to the laboratory. Oysters that tested OsHV-1 positive were placed in seawater tanks (35‰, 21°C). Water from these tanks was used to infect naive oysters in 2 experimental setups: (1) oysters acclimated or non-acclimated to a salinity of 10, 15, 25 and 35‰ and (2) oysters acclimated to a salinity of 25‰; the latter were exposed to OsHV-1 water diluted to a salinity of 10 or 25‰. The survival of oysters exposed to OsHV-1 water and acclimated to a salinity of 10‰ was 95%, compared to only 43 to 73% survival in oysters acclimated to higher salinities (Expt 1), reflecting differences in the levels of OsHV-1 DNA and viral gene expression (Expts 1 and 2). However, the survival of their non-acclimated counterparts was only 23% (Expt 2), and the levels of OsHV-1 DNA and the expression of 4 viral genes were low (Expt 1). Thus, OsHV-1 may not have been the ultimate cause of mortality in non-acclimated oysters weakened by a salinity shock. It appears that reducing disease risk by means of low salinity is unlikely in the field.

Highlights

Since 2008, massive mortality events of young Pacific oysters Crassostrea gigas have been reported in France (Miossec et al 2009, EFSA AHAW 2010, Barbosa Solomieu et al 2015, Pernet et al 2016)
These mortality events are associated with the infection of oysters with a newly described genotype of ostreid herpesvirus 1 (OsHV-1) (Segarra et al 2010)
The levels of OsHV-1 DNA and the expression of 4 viral genes in oysters were lower at 10 ‰ than at other salinities

Summary

Introduction

Since 2008, massive mortality events of young Pacific oysters Crassostrea gigas have been reported in France (Miossec et al 2009, EFSA AHAW 2010, Barbosa Solomieu et al 2015, Pernet et al 2016). These mortality events are associated with the infection of oysters with a newly described genotype (μVar) of ostreid herpesvirus 1 (OsHV-1) (Segarra et al 2010). A causal relationship between OsHV-1 and oyster mortality has been established (Schikorski et al 2011, EFSA AHAW 2015). Salinity influences host−pathogen interactions by acting directly on the pathogen, the host or both, and it can modulate the severity of the disease

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