Preventing and mitigating farmed bivalve diseases

Project Information

VIVALDI

Grant agreement ID: 678589

DOI

10.3030/678589

Project closed

EC signature date 9 February 2016

Start date 1 March 2016

End date 29 February 2020

Funded under

• SOCIETAL CHALLENGES - Food security, sustainable agriculture and forestry, marine, maritime and inland water research, and the bioeconomy

Total cost

€ 5 414 417,50

EU contribution

€ 4 503 082,50

Coordinated by

INSTITUT FRANCAIS DE RECHERCHE POUR L'EXPLOITATION DE LA MER
France

Periodic Reporting for period 3 - VIVALDI (Preventing and mitigating farmed bivalve diseases)

Reporting period: 2019-03-01 to 2020-02-29

Summary of the context and overall objectives of the project

The European shellfish industry is a major contributor to global production of marine bivalves and has a significant social impact. Since 2008, massive mortality outbreaks in Pacific oyster spat have been reported, attributed to the oyster herpesvirus OsHV-1. More recently, increased mortality has been reported in adult Pacific oysters, associated with Vibrio aestuarianus and among blue mussels with the detection of V. splendidus. Similarly, the Brown Ring Disease caused by V. tapetis and Perkinsosis have a significant impact on the production of clams. In Spain, the parasite Marteilia cochillia has contributed to the collapse of cockle fishery since 2012. Disease management methods rely, among others, on preventive measures, which are regulated at EU level.
VIVALDI has brought new knowledge on the interactions between shellfish, environment and pathogens and has developed practical tools and approaches aimed at better preventing and controlling diseases in the main European shellfish species. These species include oysters (Crassostrea gigas and Ostrea edulis), mussels (Mytilus edulis and M. galloprovincialis), clams (Ruditapes philippinarum) and scallops (Pecten maximus). The project has addressed the most harmful pathogens affecting these species: the virus Ostreid herpesvirus 1 (OsHV-1), Vibrio species including V. aestuarianus, V. splendidus and V. tapetis, as well as micro- eukaryotes such as the parasites Perkinsus olseni, Marteilia refringens, and Bonamia ostreae.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Pathogen diversity and lifecycles:
- Investigations on oyster pathogens’ genomes show that the virus OsHV-1 is evolving via animal transfers and depending on host speciesr;
- Differences in the virulence of the bacteria Vibrio aestuarianus have been revealed;
- Next Generation Sequencing has allowed us to characterise new pathogens and revealed the presence of micro-eukaryotes such as haplosporidians and mikrocytids in bivalve and environmental samples;
- The creation of a MALDI-TOF MS database will allow diagnostic laboratories to rapidly identify bacteria;
- Diagnostic approaches such as passive sensors allow to successfully detect aquatic pathogens in sea water; Magnetic Beads could be used prior to PCR to improve the detection OsHV-1 in aquaculture facilities.
Host and pathogen response:
- Important pathways involved in the bivalves’ response against pathogens were identified: e.g. autophagy (mechanism contributing to cellular components degradation and recycling), seems involved in the oyster defence against the virus OsHV-1;
- We have discovered that mussels show an extremely high expression of antimicrobial peptides that might be very effective against pathogens;
- Tissular distribution and pathogenesis of oyster pathogens OsHV-1 and Vibrio aestuarianus and the bacteria Vibrio tapetis in clams have been successfully explored;
- Improved survival of oysters challenged with UV inactivated OsHV-1 has been revealed.
Development of selective breeding programmes:
- We have produced and identified oyster tolerant families (able to support high viral load without dying) and resistant families (able to limit the infection);
- A massive genotyping approach based on 20 000 SNPs (Single Nucleotide Polymorphisms) combined with whole genome sequencing has allowed us to identify genomic regions associated with the resistance/tolerance to the viral infection;
- Parentage assignation tools based on SNP panels were developed and tested in oysters and clams;
- Simulation exercises have shown that it is possible to select for survival and growth without increasing inbreeding.
Microbiota:
- Bacterial and protist communities were investigated in bivalves under different environmental conditions and infections;
- Experimental studies have shown that oyster depuration does not remove Vibrio from bivalve tissues and exposure to nanoparticles such as n- TiO2 modifies the composition of the bacteriome;
- These first results suggest that microbiota could be used as a health marker.
Environmental parameters:
- Environmental parameters influence disease development: OsHV-1 infection is drastically reduced at 29°C or increased in the presence of green algae;
- Laboratory and field experiments have highlighted interactions between plankton and Vibrio;
- Modelling the spread of pathogens by water currents was achieved. Such models are of interest to simulate outbreak and test the efficiency of management measures.
Disease management measures:
- Strategies to avoid OsHV-1 in hatcheries/nurseries and reduce mortalities were reviewed;
- Field experiments confirm that husbandry practices need to be locally adapted;
- We have demonstrated that UV-based technology inactivates pathogens in the water in entrance of hatcheries/nurseries but also oyster gametes and larvae from the wastewater. In addition, antimicrobial photodynamic therapy appears as a promising approach to decontaminate water in hatcheries;
- A model aiming to categorising shellfish farms depending on the risk of introduction and spread of oyster pathogens was designed. This tool will help the competent authorities in Member States to better implement risk-based surveillance;
- Stakeholder analysis and mapping was carried out in several countries so as to better identify the key stakeholders in the shellfish industry and improve communication flows. A risk-perception analysis was carried out, based on individual and group interviews. The critical importance of variation in beliefs and priorities across locations, mollusc species, and stakeholder categories was highlighted. These differences should to be taken into account for prevention strategies implemented at EU and national levels;
- This work has facililated a co construction approach involving VIVALDI scientists, producers, hatcheries and competent authorities, who identified recommendations to improve biosecurity and disease management. These recommendations have been gathered under a manual that will be disseminated at large throughout the EU.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

- Characterizing the diversity of oyster pathogens: these results are of interest for future detection tools;
- Passive sensors, magnetic beads and electrochemical biosensors to improve the detection aquatic pathogens: such tools will be useful for pathogen surveillance in the environment and development of early warning systems;
- Better understanding of the life-cycles of some pathogens is required to develop effective disease management plans;
- Characterizing bivalve microbiome under different scenarios could help to identify bivalve health markers;
- Identifying key mechanisms involved in the response of bivalves during an infection may help to identify markers related with resistance against diseases;
- Panels of SNP markers are now available for oysters and clams. Combined with oyster and clam phenotyping, these panels will allow optimizing breeding programmes in combination with Marker panels for parentage assignment;
- Existing strategies to avoid OsHV-1 in hatchery/nursery were identified and completed by field studies, so as to identify the best husbandry practices to reduce mortality;
- UV treatment showed efficacy to inactivate pathogens and remove oyster gametes and larvae from the wastewater;
- By disseminating VIVALDI’s results to producers and competent authorities, the manual for biosecurity and disease management measures will contribute to prevent and mitigate effect of bivalve diseases.

VIVALDI project

Water treatment, to better prevent the entry of pathogens in nurseries and hatcheries

Modeling to better predict shellfish diseases

Dissemination activities

Studying the diversity of pathogens, such as Marteilia Refringens (parasite)

Oyster selection programmes to increase resistance/tolerance to diseases

Sampling in Ria de Vigo (ES)

Studying the autophagy pathway to better understand the virus/oyster interactions