CE20 - Biologie des animaux, des organismes photosynthétiques et des microorganismes

Deciphering the whole complexity of the Pacific oyster mortality syndrome for modeling epidemiological risk. – DECICOMP

DECICOMP

Deciphering the whole complexity of the Pacific oyster mortality syndrome for modeling epidemiological risk.

POMS a disease still misunderstood

The Pacific oyster (Crassostreae gigas) has been introduced from Asia to numerous countries throughout the world (including Canada, USA, Australia, New-Zealand, Chile, Argentina, France) during the 20th century. C. gigas is currently the main oyster species farmed in the world and represents more than 95% of world production. For decades, C. gigas has been suffering mortalities but the severity of these outbreaks has dramatically increased since 2008. They mainly affect juvenile stages, decimating up to 100% of young oysters in French farms. In recent years, this mortality syndrome, designated Pacific oyster mortality syndrome (POMS), has become panzootic and represents a threat for the oyster industry worldwide. Recently, the consortium of the DECICOMP project overcame a major step towards understanding POMS using a holistic molecular approach developed in mesocosm. We showed that the infection by the Ostreid herpesvirus (OsHV-1 µVar) was the initial step of the infectious process leading to an immune-compromised state, which evolved towards subsequent bacteraemia by opportunistic bacterial pathogens. Nevertheless, by elucidating the mechanisms of the pathogenesis, only a part of the POMS complexity was deciphered. Indeed, this multifactorial disease is tightly controlled by a series of host and environmental factors (temperature, oyster age and diet). However, we still ignore the mechanisms by which these key factors control disease expression. This knowledge is urgently needed to elucidate the whole complexity of the disease and ultimately assess the epidemiological risk. In this context, the first objective of the DECICOMP project is to determine how temperature, oyster age and diet control POMS expression. The second objective is to weight and evaluate the interactions between all these factors in real farming conditions. Finally, our third objective is to model the epidemiological risk of POMS in oyster farms by using the sum of data generated in the project.

To address the objectives of the DECICOMP project, we will combine experimental/field experiments and theoretical approaches. Our multidisciplinary approach (mesoscosm and rationalized infections, integrative omics including epigenomics and metatranscriptomics, physiological/histological/functional validation approaches, modelling) is unique, ambitious and, as we believe, highly original. To reach our objectives, we have put together a consortium of researchers with highly complementary expertise that makes possible the implementation of a multiscale approach for deciphering the functioning of such a complex pathosystem from the finest molecular level to farmed populations.

Biparental oyster families with contrasting phenotypes were produced in the spring and mesocosm experiments were carried out at the end of August 2020 . The phenotypes of interest and the protective effect of diet and non-permissive temperatures (<16 ° C and> 24 ° C) have been obtained.
Ecophysiological and bioenergetic measurements on oysters have been carried out and are being analyzed. The quantifications of pathogens (viral / bacterial load in oysters, in the water column) and histological analyzes (HIS and classical histology) are in progress. Transcriptomic and metatranscriptomic analyzes are in progress on oysters under different conditions. Epigenomic sequencing will begin next months.

We believe DECICOMP will not only open prospects for substantial scientific knowledge advancement on a complex multifactorial disease but will also help decision-making thanks to tools and applied innovations for a sustainable and integrated management of oyster aquaculture. Indeed, by modelling the epidemiological risk under the influence of the different factors influencing POMS, we will be able to quantify the benefits of different measures that could be conducted by oyster farmers to play on these factors and consequently provide some action-levers to reduce the impact of the disease in farms.

1. DE LORGERIL J., PETTON B., LUCASSON A., PEREZ V., STENGER P.L., DEGREMONT L., MONTAGNANI C., ESCOUBAS J.M., HAFFNER P., ALLIENNE J.F., LEROY M., LAGARDE F., VIDAL-DUPIOL J., GUEGUEN Y., MITTA G. (2020). Differential basal expression of immune genes confers Crassostrea gigas resistance to Pacific Oyster Mortality Syndrome. BMC Genomics, 21(1):63. doi: 10.1186/s12864-020-6471-x.

The Pacific oyster (Crassostreae gigas) has been introduced from Asia to numerous countries throughout the world (Canada, USA, Australia, New-Zealand, Chile, Mexico, Argentina, South Africa, Namibia and in numerous European countries including France) during the 20th century. C. gigas is currently the main oyster species farmed in the world and represents more than 95% of world production. For decades, C. gigas has been suffering mortalities but the severity of these outbreaks has dramatically increased since 2008. They mainly affect juvenile stages, decimating up to 100% of young oysters in French farms. In recent years, this mortality syndrome, designated Pacific oyster mortality syndrome (POMS), has become panzootic and represents a threat for the oyster industry worldwide. Recently, the consortium of the DECICOMP project overcame a major step towards understanding POMS using a holistic molecular approach developed in mesocosm. We showed that the infection by the Ostreid herpesvirus (OsHV-1 µVar) was the initial step of the infectious process leading to an immune-compromised state, which evolved towards subsequent bacteraemia by opportunistic bacterial pathogens. Nevertheless, by elucidating the mechanisms of the pathogenesis, only a part of the POMS complexity was deciphered. Indeed, this multifactorial disease is tightly controlled by a series of host and environmental factors (temperature, oyster age and diet). However, we still ignore the mechanisms by which these key factors control disease expression. This knowledge is urgently needed to elucidate the whole complexity of the disease and ultimately assess the epidemiological risk. In this context, the first objective of the DECICOMP project is to determine how temperature, oyster age and diet control POMS expression. The second objective is to weight and evaluate the interactions between all the factors controlling POMS in real farming conditions. Finally, our third objective is to model the epidemiological risk of POMS in oyster farms by using the sum of data generated in the project. To address the objectives of the DECICOMP project, we will combine laboratory/field experiments and theoretical approaches. Our multidisciplinary approach (mesoscosm and rationalized infections, integrative omics including epigenomics and metatranscriptomics, physiological/histological/functional validation approaches, modelling) is unique, ambitious and, as we believe, highly original. To reach our objectives, we have put together a consortium of researchers with highly complementary expertises that makes possible the implementation of a multiscale approach for deciphering the functioning of such a complex pathosystem from the finest molecular level to farmed populations. We believe DECICOMP will not only open prospects for substantial scientific knowledge advancement on a complex multifactorial disease but will also help decision-making thanks to tools and applied innovations for a sustainable and integrated management of oyster aquaculture. Indeed, by modelling the epidemiological risk under the influence of the different factors influencing POMS, we will be able to quantify the benefits of different measures that could be conducted by oyster farmers to play on these factors and consequently provide some action-levers to reduce the impact of the disease in farms.

Project coordinator

Monsieur Guillaume Mitta (Interactions Hôtes-Pathogènes-Environnements)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LEMAR LABORATOIRE DES SCIENCES DE L'ENVIRONNEMENT MARIN
LBI2M Laboratoire de Biologie intégrative des modèles marins
RBE-SG2M Santé, Génétique et Microbiologie des Mollusques
MIVEGEC Maladies Infectieuses et Vecteurs : Ecologie, Génétique, Evolution et Contrôle
IHPE Interactions Hôtes-Pathogènes-Environnements

Help of the ANR 664,210 euros
Beginning and duration of the scientific project: December 2019 - 48 Months

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