First comparison of French and Australian OsHV-1 µvars by bath exposure.

Ca Burge,Cs Friedman,Ks Reece,Ak Dhar,P Kirkland,B Morga,N Faury,A Macintyre,Bjt Wippel,L Dégremont

doi:10.3354/dao03452

Abstract

Economically devastating mortality events of farmed and wild shellfish due to infectious disease have been reported globally. Currently, one of the most significant disease threats to Pacific oyster Crassostrea gigas culture is the ostreid herpesvirus 1 (OsHV-1), in particular the emerging OsHV-1 microvariant genotypes. OsHV-1 microvariants (OsHV-1 µvars) are spreading globally, and concern is high among growers in areas unaffected by OsHV-1. No study to date has compared the relative virulence among variants. We provide the first challenge study comparing survival of naïve juvenile Pacific oysters exposed to OsHV-1 µvars from Australia (AUS µvar) and France (FRA µvar). Oysters challenged with OsHV-1 µvars had low survival (2.5% exposed to AUS µvar and 10% to FRA µvar), and high viral copy number as compared to control oysters (100% survival and no virus detected). As our study was conducted in a quarantine facility located ~320 km from the ocean, we also compared the virulence of OsHV-1 µvars using artificial seawater made from either facility tap water (3782 µmol kg-1 seawater total alkalinity) or purchased distilled water (2003 µmol kg-1). Although no differences in survival or viral copy number were detected in oysters exposed to seawater made using tap or distilled water, more OsHV-1 was detected in tanks containing the lower-alkalinity seawater, indicating that water quality may be important for virus transmission, as it may influence the duration of viral viability outside of the host.

Highlights

A robust aquaculture industry is dependent on understanding risks, such as disease, that affect production
Survival was low in oysters exposed to either ostreid herpesvirus 1 (OsHV-1) μvar and was significantly lower in those exposed to the AUS μvar (2.5%) than to the FRA μvar (10%) (p = 0.004, log-rank test statistic = 8.50, df = 1, Fig. 1)
The mean survival time was 3.58 ± 0.17 d for oysters exposed to the AUS μvar, and 4.33 ± 0.23 d for oysters exposed to the FRA μvar

Summary

Introduction

A robust aquaculture industry is dependent on understanding risks, such as disease, that affect production. Dis Aquat Org 138: 137–144, 2020 ter aquaculture, the ostreid herpesvirus 1 (OsHV-1) and its variants are considered one of the most significant threats to culture of this species globally (Barbosa-Solomieu et al 2015). OsHV-1 and its variants, the OsHV-1 microvariants (μvars), are virulent and problematic viruses of larval, seed, and adult Pacific oysters (reviewed by Barbosa-Solomieu et al 2015, Pernet et al 2016, Burge et al 2018). In the 1990s, losses of larval and juvenile oysters associated with OsHV-1 were first described in France, New Zealand, and the USA (reviewed by Burge et al 2018). Sequence variations in some genomic regions have been observed among the different OsHV-1 μvars (BarbosaSolomieu et al 2015, Abbadi et al 2018), a complete understanding of strain variation and how this impacts virus phenotype remains unknown

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Conclusion