#	Pagina
attuale pagina	/open-h2020/projects/195715/results.html

Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ResisGal (Ostreid herpesvirus 1: Genetic selection of Resistant strains and environmental interaction in the Atlantic coast of Spain (Galicia))

Teaser

Summary

One of the main concerns in the aquaculture sector is the significant mortality of the Pacific oyster, Crassostrea gigas, the principal shellfish cultivated worldwide. Among other factors, the incidence of a virus (OsHV-1) has been directly associated with these mortality events which can largely exceed normal losses. The economic impact of the disease in oyster production has reached worrying levels since it has been spread to producer countries in both hemispheres.
Shellfish are hard to treat when exposed to disease due to the high population densities involved, the environment in which they are found and that immunisation is not a possibility due to their lack of an adaptive immune response. Treatment and control mechanisms tend to focus on long term solutions such as identification of resistant traits and breeding for the inclusion of these traits. In this study, resistant strains will be genetically characterized and investigated in the field in order to identify the molecular markers required for assisted selection in future breeding programs. The relationship between environmental parameters, virus transmission between species and virus prevalence will be further studied with the aim of establishing less risky conditions for culture.
Objectives of the study:
1. To identify the markers associated with virus resistance in spat produced by genetic selection.
2. To characterize the epigenetic regulation that may be operating in genes related to virus resistance.
3. To investigate the incidence of OsHV-1 in the octopus and determine its role as virus reservoir
4. To determine if DNA from sea water could be used as a predictable signal of oyster mortality.

Work performed

The work performed has consisted of:
1. The production of oyster families attending to different susceptibility to OsHV-1. Two broodstock were compared: survivors from a mortality event and naÃ¯ve oysters - never exposed to the virus. Progenies were exposed to the OsHV-1 in the field and after a mortality event oyster mortality, prevalence of infection, genotyping on selected transcripts and epigenetic variation were compared.
2. A field survey of sea water and a cultured oyster stocks on two sites to evaluate the incidence of OsHV-1 in eDNA and host DNA and to study the effect of different environmental conditions and growth systems on oyster mortality.
3. A retrospective study on common octopus to study the incidence of OsHV-1 and a set of experimental trials to evaluate the transmission between species and the direct effect of the virus on octopus in terms of mortality, prevalence, virus replication and host gene expression.

Overview of the results:
Progenies of oysters with different susceptibility to the virus showed different levels of mortality and prevalence of OsHV-1 after a natural mortality event occurred in the field. The genotyping analysis of molecular markers associated to differently expressed genes under infection showed up a number of markers associated to resistance to OsHV-1. The epigenetic regulations by DNA methylation was corroborated in susceptible animals. Resistant animals showed inherent genetic modifications with might be related to the process of selection itself.
The progression of the OsHV-1 infection in spat oysters might be largely influenced by environmental conditions and basal prevalence. Combination of both parameters can contribute to a process of massive mortality or survival. It was observed that high basal OsHV-1 prevalence under moderate risky environmental conditions did not lead to oyster mortality whereas low prevalence combined with an increased risky natural situation developed in abnormal mortalities.
The incidence of OsHV-1 on the common octopus was corroborated by molecular methods of detection and OsHV-1 seemed to be transmitted between species. The octopus immune defense was activated after virus exposures. However, an evidence of virus replication in octopus tissues were not confirmed which put on doubt the progress of an infection in this species.

Final results

Conclusions derived from this work are beneficial to the European scientific community and can be applied in countries affected by the OsHV-1 all over the world. The research carried out in this project was aligned with the H2020 Societal Challenge â€˜Food security, sustainable agriculture and forestry, marine and maritime and inland water research and the bioeconomyâ€™ which has remarked a â€œspecial emphasis on OsHV-1, in order to better understand genetic diversity, pathogens spread, pathogenicity and key drivers of emergence in relevant parts of the worldâ€.
This project aimed with the impact expected for the problem related to OsHV-1 since new practical information is now available regarding the culture of this species, the reservoirs and the spread of the disease between species and also the very valuable information on the genetic basis and molecular markers that select resistant oysters for selective breeding which will be of high interest also for the industry sector.