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Shellfish Health in the UK - FC1205

This project will be arranged into four distinct pillars which offer stand-alone outputs but will also provide an improved understanding of key disease agents in sentinel invertebrates from the UK marine environment. Pillars 1 to 3 focus on significant issues of policy concern, particularly regarding the EC Directive 2006/88 listed pathogens of molluscan shellfish. Pillar 4 builds upon a previous Defra contract (FC1186) and will provide initial molecular evidence for the basis of viral management (for the EC Directive listed virus WSSV) in crustacean hosts. Together, the work programme within these pillars emphasizes the current and future importance of invertebrates (and their diseases) in capture and culture production from the UK marine environment.

Pillar 1: Paramyxean taxonomy
Focusing on the phylogenetics and ultrastructure of Marteilia sp. in molluscan hosts from UK waters, the project will provide a definitive statement on the relationship between Marteilia maurini and Marteilia refringens issue by utilization of transmission EM, laser capture microscopy and potentially, next generation sequencing of isolates. The study will investigate the presence, pathogenesis and taxonomy of Marteilia spp. from mussels and oysters and will deliver specific evidence for policy decisions regarding this listed pathogen. In a second component of pillar 1, we will carry out a phylogenetic assessment of the edible crab and spider crab pathogen Paramarteilia canceri (Feist et al. 2009) and will define the relationship between this parasite and the Marteilia spp. from oysters and mussels. This will allow for investigation of potential for multi-trophic presence of paramyxeans in invertebrate hosts from UK marine habitats.

Pillar 2: Haplosporidia of shoreline communities
Recent finding of the asporous Haplosporidium littoralis n.sp. (Stentiford et al., 2011) in up to 80% of juvenile edible crabs from the English channel shoreline, and its close relationship with co-generic parasites from European limpets and abalone suggest that crustaceans and molluscs may share pathogens in a manner not previously investigated. In this pillar we will carry out a shoreline survey of H. littoralis positive areas to investigate potential for life cycle variants of important pathogens within these host groups. Histological, ultrastructural and molecular tools already developed for H. littoralis detection will be utilized to screen candidate host species in the littoral environment. Similar tools will also be utilized to investigate the potential for co-occurrence of the haplosporidian Bonamia ostrea and Bonamia exitiosa. Further, approaches developed for H. littoralis will be used to similarly investigate potential for the asporous Bonamia sp. to possess life cycle stages in other host taxa.

Pillar 3: Molluscs as pathogen sinks
Despite specific information relating to the presence of important pathogens in harvested molluscan shellfish, little effort has been directed to the detection of pathogens in native wild populations. In many regions, these native populations inhabit the same sites as harvested stock and therefore have the potential to act as reservoirs for pathogens causing disease outbreak in culture scenarios (e.g. Oyster Herpes Virus). Conversely, pathogens/disease states arising from intensive culture may impact upon wild populations in adjacent waters. In this pillar we will assess the potential for wild stocks of mussels (Mytilus spp.) to act as a ‘sentinel’ for potential outbreaks of disease in culture scenarios and to investigate the potential for development of a UK-wide pathogen ‘risk-map’ that may be utilised for assessing suitable regions for the on-growing of molluscan shellfish. This pillar will also investigate the effect of age/size on pathogen profile in the sentinel from UK waters.

Pillar 4: The invertebrate host-pathogen interface
Previous work at the Cefas Weymouth laboratory has demonstrated the potential for exotic viral pathogens (such as WSSV) to infect, cause disease, and kill, a wide range of decapod crustaceans from UK waters (Defra project FC1186). Inherent within this dataset however is a wide-range of relative host susceptibility (from rapid disease progression in some hosts, to recalcitrance in others). Utilising emerging tools (next generation sequencing), the full genome sequence of the viral pathogen WSSV, and the ability to expose a range of decapod host models to the virus, we aim to investigate the role of host microRNAs (miRNAs) in abating the infection/disease process in these hosts. We will utilise the European shore crab (Carcinus maenas) as a model. This work in this pillar will link with a Cefas Seedcorn-funded project. Together the projects will contribute to an improved understanding of viral management in crustacean hosts and may be expanded to provide a mechanism to rapidly assess susceptibility of aquatic hosts to a range of important pathogens.
Objective 1: To carry out a detailed genomic comparison of the 'm' type and 'o' type isolates of Marteilla sp. from mussels and oysters, respectively. To investigate homology across larger regions of the respective genomes.
Objective 2: To carry out a phylogenetic assessment of Paramarteillia canceri infecting the European edible crab (Cancer pagrus) and to compare specific genome regions to Marteilla spp. infecting bivalve molluscs.
Objective 3: To investigate potential reservoir hosts of classical molluscan pathogens using the model of Haplosporidium littoralis (infecting Cancer pagurus) and Bonamia sp. (infecting oysters) via multi-trophic sampling of communities residing in endemic habitats.
Objective 4: To investigate the utilization of 'sentinel' populations of molluscs (mussels) for generation of a pathogen/disease 'risk-map' for specific locations in the UK. Locations(s) to be chosen based upon acess to inshore/offshore farming programmes and proximity of wild populations.
Objective 5: To classify novel pathogens encountered during Objectives 3 & 4.
Objective 6: To generate suitable material for miRNA transcriptomic studies via exposure of high-susceptible and low-susceptible crustacean hosts to the EC-listed viral pathogen WSSV.
Time-Scale and Cost
From: 2012

To: 2015

Cost: £405,000
Contractor / Funded Organisations
Fish Disease              
Fish Farming