Interaction between the Pacific oyster Crassostrea gigas and the Ostreid herpesvirus OsHV-1 : influence of salinity and pH

Crassostrea gigas est l’espèce d’huître la plus cultivée au monde. Depuis 2008, des évènements de mortalité massive touchent les huîtres âgées de moins d’un an en Europe et en Océanie et ont été associés à l’émergence d’un nouveau variant de l’Ostréid herpèsvirus type 1, OsHV-1 μvar. Les huîtres sont naturellement présentes dans les écosystèmes estuariens et côtiers, caractérisés par des fluctuations de salinité et de pH. Dans le cadre de ce travail, l’effet de la salinité (10, 15, 25, 35‰) et du pH (7.8, 8.1) sur la réponse de l’huître à une infection par OsHV-1 a été étudié. La survie d’huîtres acclimatées à une salinité de 10‰ préalablement à l’exposition à une source infectieuse est de 95% et s’explique par une diminution de l’infectiosité d’OsHV-1. En revanche, la survie d’huîtres non-acclimatées simultanément soumises à un choc de salinité à 10‰ et exposées à une source infectieuse n’est que de 23%, ce qui reflète un affaiblissement physiologique. La survie (S) des huîtres aux autres salinités est classée de la manière suivante : S15‰ > S35‰ > S25‰ et selon le pH comme suit : SpH 7.8 S35‰ > S25‰ and according to pH as follows: SpH 7.8 < SpH 8.1. In both studies these contrasts of survival are not explained by differences in OsHV-1 infectivity but in host metabolic response. The carbohydrate metabolism and antioxidant activity of oysters acclimated to 25 and 35‰ is higher than in oysters at 10-15 ‰ and could explain the lower survival. Lower antioxidant activity is observed in oysters maintained at pH 7.8 likely reflecting a reduced production of reactive oxygen species and the maintenance of a basal production of nitrogen reactive species despite infection. This might impair the defense ability of oysters to OsHV-1 explaining the reduced survival at pH 7.8 in comparison to what observed at pH 8.1

Interaction entre l'huître creuse Crassostrea gigas et l'Ostréid herpèsvirus OsHV-1 : influence de la salinité et du pH

Crassostrea gigas is the most cultivated oyster species around the world. Since 2008, mass mortality events have been affecting oysters aged less than one year old in Europe, and Oceania and have been associated with a new variant of the ostreid herpesvirus type 1, OsHV-1 μvar. Oysters live in estuaries and bays where they are exposed to fluctuations of salinity and pH. In the present work, the effect of salinity (10, 15, 25, 35 ‰) and pH (7.8, 8.1) on the response of oysters to infection by OsHV-1 was investigated. The survival of oysters acclimated to 10 ‰ prior to be exposed to a source of infection is 95% and is explained by a reduction of OsHV-1infectivity. In contrast, the survival of non-acclimated oysters simultaneously submitted to a salinity stress at 10 ‰ and exposed to a source of infectious is only 23%, likely reflecting physiological impairment. The survival (S) of oysters in other salinity treatment is ranked as follow: S15‰ > S35‰ > S25‰ and according to pH as follows: SpH 7.8 S35‰ > S25‰ et selon le pH comme suit : SpH 7.8 < SpH 8.1. Dans les deux études ces contrastes de survie ne sont pas expliqués par un différentiel d’infectiosité du virus mais par celui de la réponse métabolique de l’hôte. Le métabolisme des sucres et l’activité antioxydante d’huîtres acclimatées à 25 et 35‰ sont supérieurs à celui d’huîtres à 10-15‰ et pourraient expliquer leur moindre survie. La plus faible activité antioxydante observée chez des huîtres maintenues à pH 7.8 suggère une production réduite d’espèces réactives de l’oxygène et le maintien d’une production basale d’espèces réactives de l’azote malgré l’infection, ce qui aurait pu réduire la capacité de défense des huîtres face au virus et expliquer leur moindre survie en comparaison à ce qui est observé à pH 8.1

Deciphering the effect of food availability, growth and host condition on disease susceptibility in a marine invertebrate

WOS:000485288700024International audienceFood provisioning influences disease risk and outcome in animal populations in two ways. On the one hand, unrestricted food supply improves the physiological condition of the host and lowers its susceptibility to infectious disease, reflecting a trade-off between immunity and other fitness-related functions. On the other hand, food scarcity limits the resources available to the pathogen and slows the growth and metabolism of the host on which the pathogen depends to proliferate. Here, we investigated how food availability, growth rate and energetic reserves drive the outcome of a viral disease affecting an ecologically relevant model host, the Pacific oyster, Crassostrea gigas. We selected fast- and slow-growing animals, and we exposed them to high and low food rations. We evaluated their energetic reserves, challenged them with a pathogenic virus, monitored daily survival and developed a mortality risk model. Although high food levels and oyster growth were associated with a higher risk of mortality, energy reserves were associated with a lower risk. Food availability acts both as an enabling factor for mortality by increasing oyster growth and as a limiting factor by increasing their energy reserves. This study clarifies how food resources have an impact on susceptibility to disease and indicates how the host's physiological condition could mitigate epidemics. Practically, we suggest that growth should be optimized rather than maximized, considering that trade-offs occur with disease resistance or tolerance

Low pH reduced survival of the oyster Crassostrea gigas exposed to the Ostreid herpesvirus 1 by altering the metabolic response of the host

WOS:000458730400020International audienceEnvironmental change in the marine realm has been accompanied by emerging diseases as new pathogens evolve to take advantage of hosts weakened by environmental stress. Here we investigated how an exposure to reduced seawater pH influenced the response of the oyster Crassostrea gigas to an infection by the Ostreid herpesvirus type I (OsHV-1). Oysters were acclimated at pH 8.1 or pH 7.8 and then exposed to OsHV-1. Their survival was monitored and oyster tissues were sampled for biochemical analyses. The survival of oysters exposed to OsHV-1 at pH 7.8 was lower (33.5%) than that of their counterparts at pH 8.1 (44.8%) whereas levels of OsHV-1 DNA were similar. Energetic reserves, fatty acid composition and prostaglandin levels in oyster did not vary consistently with pH, infection or their interactions. However, there was a reduction in the activities of superoxide dismutase (SOD) and nitric oxide synthase (iNOS) in oysters at low pH, which is associated with the observed difference in survival

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

International audienceMortality 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 degrees 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 \textgreater 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

The Voltage-Dependent Anion Channel (VDAC) of Pacific Oysters Crassostrea gigas Is Upaccumulated During Infection by the Ostreid Herpesvirus-1 (OsHV-1): an Indicator of the Warburg Effect

WOS:000424459500008International audienceVoltage-dependent anion channel (VDAC) is a key mitochondrial protein. VDAC drives cellular energy metabolism by controlling the influx and efflux of metabolites and ions through the mitochondrial membrane, playing a role in its permeabilization. This protein exerts a pivotal role during the white spot syndrome virus (WSSV) infection in shrimp, through its involvement in a particular metabolism that plays in favor of the virus, the Warburg effect. The Warburg effect corresponds to an atypical metabolic shift toward an aerobic glycolysis that provides energy for rapid cell division and resistance to apoptosis. In the Pacific oyster Crassostrea gigas, the Warburg effect occurs during infection by Ostreid herpesvirus (OsHV-1). At present, the role of VDAC in the Warburg effect, OsHV-1 infection and apoptosis is unknown. Here, we developed a specific antibody directed against C. gigas VDAC. This tool allowed us to quantify the tissue-specific expression of VDAC, to detect VDAC oligomers, and to follow the amount of VDAC in oysters deployed in the field. We showed that oysters sensitive to a mortality event in the field presented an accumulation of VDAC. Finally, we propose to use VDAC quantification as a tool to measure the oyster susceptibility to OsHV-1 depending on its environment

Determination of risk factors for herpesvirus outbreak in oysters using a broad-scale spatial epidemiology framework

Marine diseases have major impacts on ecosystems and economic consequences for aquaculture and fisheries. Understanding origin, spread and risk factors of disease is crucial for management, but data in the ocean are limited compared to the terrestrial environment. Here we investigated how the marine environment drives the spread of viral disease outbreak affecting The Pacific oyster worldwide by using a spatial epidemiology framework. We collected environmental and oyster health data at 46 sites spread over an area of 300 km2 along an inshore-offshore gradient during an epizootic event and conducted risk analysis. We found that disease broke out in the intertidal farming area and spread seaward. Mortalities and virus detection were observed in oysters placed 2 km from the farming areas, but oysters of almost all sites were subclinically infected. Increasing food quantity and quality, growth rate and energy reserves of oyster were associated with a lower risk of mortality offshore whereas increasing turbidity, a proxy of the concentration of suspended particulate matter, and terrestrial inputs, inferred from fatty acid composition of oysters, were associated with a higher risk of mortality. Offshore farming and maintenance of good ecological status of coastal waters are options to limit disease risk in oysters

Evaluation of the Accelerate Pheno\texttrademark system for rapid identification and antimicrobial susceptibility testing of Gram-negative bacteria in bloodstream infections

International audienceIdentification and antimicrobial susceptibility testing (AST) are critical steps in the management of bloodstream infections. Our objective was to evaluate the performance of the Accelerate Pheno\texttrademark System, CE v1.2 software, for identification and AST of Gram-negative pathogens from positive blood culture bottles. A total of 104 bottles positive for Gram-negative bacteria collected from inpatients throughout our institution were randomly selected after Gram staining. The time-to-identification and AST results, and the raw AST results obtained by the Accelerate Pheno\texttrademark system and routine techniques (MALDI-TOF MS and VITEK\textregistered2, EUCAST guidelines) were compared. Any discrepant AST result was tested by microdilution. The Pheno\texttrademark significantly improved turn-around times for identification (5.3 versus 23.7~h; p \textless 0.0001) and AST (10.7 versus 35.1~h; p \textless 0.0001). Complete agreement between the Accelerate Pheno\texttrademark system and the MALDI-TOF MS for identification was observed for 96.2% of samples; it was 99% (98/99) for monomicrobial samples versus 40% (3/5) for polymicrobial ones. The overall categorical agreement for AST was 93.7%; it was notably decreased for beta-lactams (cefepime 84.4%, piperacillin-tazobactam 86.5%, ceftazidime 87.6%) or Pseudomonas aeruginosa (71.9%; with cefepime 33.3%, piperacillin-tazobactam 77.8%, ceftazidime 0%). Analysis of discrepant results found impaired performance of the Accelerate Pheno\texttrademark system for beta-lactams (except cefepime) in Enterobacteriales (six very major errors) and poor performance in P. aeruginosa. The Accelerate Pheno\texttrademark system significantly improved the turn-around times for bloodstream infection diagnosis. Nonetheless, improvements in the analysis of polymicrobial samples and in AST algorithms, notably beta-lactam testing in both P. aeruginosa and Enterobacteriales, are required for implementation in routine workflow

Recherche de gisements de captage naturel de Crassostrea gigas en lagune de Thau.Répartition spatiotemporelle du naissain, aspects culturaux et économiques.

Le travail est axé sur la volonté de la filière conchylicole méditerranéenne pour s'approvisionner en naissains d'huîtres creuses sauvages d’origine lagunaire. L'observatoire du captage naturel, mis en place entre 2012 et 2014, a permis de découvrir des gisements de naissains collectés naturellement dans la lagune de Thau selon un protocole défini à l’échelle expérimentale. Bien que très hétérogènes spatialement et temporellement, les densités de naissains sur les collecteurs révèlent des catégories de captage allant de "moyen i. e. 20 à 200 naissains par coupelle" à "excellent i. e. 200 à 2000 naissains par coupelle " sur certaines stations expérimentales. Les expériences de captage naturel à échelle semi-industrielle (avec filière de coupelles en lagune) ont permis de confirmer le succès du captage naturel sur les gisements favorables mais la mise en prégrossissement en zone ostréicole reste un point de blocage à ce stade de développement du projet. Les suivis de survie des lots de naissains autochtones reflètent des survies intéressantes bien que le naissain montre une sensibilité aux phénomènes de surmortalité automnale. L’étude économique montre que la pratique du captage naturel est rentable sur certaines stations situées en dehors des zones ostréicoles dont les niveaux de captage sont "moyens" à "excellents". Le réseau "Biovigilance" (pour la caractérisation de la ploïdie des huîtres sauvages) et les épreuves thermiques de laboratoire caractérisant le statut de zoo-sanitaire vis-à-vis du virus OsHV-1 permettent de définir le statut du naissain autochtone de la lagune de Thau comme étant de relative bonne qualité cytogénétique en 2013 avec un bon bilan zoo-sanitaire OsHV-1 (faiblement infecté, faiblement infectieux). Après la découverte des zones de captage de naissains d’huitre creuse, la poursuite des travaux de recherche devront, le cas échéant, s'orienter vers la recherche des zones de prégrossissement (micronurserie, nurserie) afin de maximiser la survie du captage naturel en lagune méditerranéenne