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Aims: This study was performed to develop a passive sampling methodology for the detection of two viruses in seawater in the area of shellfish production, the norovirus (NoV), a human pathogen implicated in gastroenteritis outbreaks linked to oyster consumption and the ostreid herpesvirus type 1 (OsHV-1), a virus associated with mass mortalities of Pacific oysters., Methods and Results: Commercially, membranes were tested for their capacity to adsorb virus: zetapor, gauze, nylon, low-density polyethylene (LDPE) and polyvinylidene difluoride (PVDF). Laboratory exposures of membranes to contaminated water samples (stool, sewage, seawater) were performed. Our data show that the amount of NoV GII genome per membrane measured with qRT-PCR increased with the time of exposure up to 24 h, for all types of membranes except gauze. After 15 days of exposure, the amount of NoV GII per membrane continued to increase only for nylon and LDPE. The amount of OsHV-1 per zetapor membrane was significantly increased as soon as 4 h of exposure, and after 24 h of exposure for all types of membranes. Exposure of membranes to serial dilutions of various samples revealed that the amount of NoV GII and OsHV-1 per membrane is significantly higher in diluted samples. The detection of NoV and OsHV-1, respectively, with zetapor and PVDF membranes was found to be more efficient than the direct analysis of sewage and seawater., Conclusions: All membranes immersed in contaminated samples adsorbed NoV GII and OsHV-1. The amount of both viruses increased with the time of exposure. Zetapor and PVDF membranes seem to be more adapted to NoV GII and OsHV-1 detection respectively., Significance and Impact of the Study: Membranes tested will be used as passive samplers to improve the detection of virus in oyster production areas. Also, passive samplers could be a valuable tool for microbiome analysis with new generation sequencing., (© 2017 The Society for Applied Microbiology.)

The Pacific oyster (Crassostrea gigas) is farmed globally. Ostreid herpesvirus (OsHV-1) causes severe mortalities of farmed C. gigas. Management of OsHV-1 has proven difficult. Oysters treated with poly(I:C) exhibit enhanced protection (EP) against OsHV-1. This chemical treatment is highly effective, but it is not feasible to treat every oyster on a farm. To circumvent this practical limitation, previous studies on arthropods have suggested that EP can be transferred from parents to their offspring (trans-generational EP, TGEP). This suggests that the treatment of relatively few parents could be used to produce large numbers of offspring with TGEP. Here, we investigated TGEP in oysters to test whether it might be used as a cost effective management tool to control OsHV-1. We found that offspring (D-veliger larvae) produced from poly(I:C)-treated parents had double the chance of surviving exposure to OsHV-1 compared to controls. Furthermore, the larvae of poly(I:C)-treated parents contained elevated levels of mRNA encoding a key transcription factor that regulates antiviral immunity (IRF2). Poly(I:C) treatment had no effect on the survival of oyster parents. Hence, the enhanced immunity of their offspring could not be explained by genetic selection, and instead may reflect epigenetic reprogramming or maternal provisioning., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

French production of the Pacific cupped oyster, Crassostrea gigas, is currently threatened by two pathogens, OsHV-1 and V. aestuarianus. While oysters selected for their higher resistance to OsHV-1 are now available for the industry, the impact of V. aestuarianus on such oysters is unknown, especially for triploids. In addition, experimental infection has used the virus or the bacteria alone, but there have been no investigations of dual exposure to these pathogens. This study is the first report of single or dual exposure in spat (Spat1 and Spat2), juvenile and adult naïve oysters. For each of the two stocks evaluated, unselected oysters and oysters selected for their higher resistance to OsHV-1 infection were tested, as well as their triploid siblings of the selected oysters produced using cytochalasin B. We confirmed that resistance to OsHV-1 infection and susceptibility to V. aestuarianus increased with age and size, although selected oysters were not significantly impacted by OsHV-1 whatever their ploidy, size or age. We found different mortality patterns depending on the pathogen tested. The mortality pattern was similar for oysters exposed to OsHV-1 or to both pathogens in the Spat1 trial (4months old and 1.9g). The mortality pattern was similar for oysters exposed to V. aestuarianus or to both pathogens in the Adult trial (25months old and 63.1g). Surprisingly, mortality was much higher (ranging from 75.9% to 100%), in particular for the selected oysters, for the Spat2 (8months old/3.9g) and Juvenile trials (16months old/18.4g) given a dual exposure, regardless of the level of selection for OsHV-1 and the ploidy state. Our findings highlight an important threat for oyster farmers: oysters exposed to both pathogens could experience dramatic mortality rates, even in oysters selected for their higher resistance to OsHV-1. Finally, our study demonstrated for the first time that triploid oysters were more susceptible to experimental challenges with V. aestuarianus at the spat stage than their diploid siblings. However, the difference in mortality between the triploids and diploids remained limited and ranged from 22.9% to 6.6% for spat and adults, respectively with a relatively regularly decrease in the difference with increased age., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Since the 1990s, high mortality rates of young Pacific oysters Crassostrea gigas have been regularly recorded in France and affect mainly spat (oysters less than 1 year old). Pathogens infecting marine bivalve mollusks have been studied particularly due to their economic and ecologic impacts on the farmed and wild oysters. A herpes virus belonging to the family Malacoherpesviridae and called Ostreid Herpesvirus-1 (OsHV-1) has been detected in infected oysters. Since the summer 2008, the mortality of spat has greatly increased on the French coast (with a mortality rate ranging from 40 to 80%) and may be linked to a variant of the OsHV-1, named OsHV-1 μVar. Few variants of the OsHV-1 and genotypes closed to the OsHV-1 μVar have been described in several areas in the world. However, the OsHV-1 μVar is predominant in analyzed samples and the reference genotype of the OsHV-1 has not been detected since 2008. The causes of the emergence of the OsHV-1 μVar and its rapid spreading in the world are currently unknown.