Modelling Ostreid Herpesvirus Transmission in Mixed-Species Oyster Population.
Supervisors: Gorka Bidegain (UPV/EHU), Tal Ben-Horin (North Carolina State University)
Recent decades have seen Pacific oyster (Crassostrea gigas) aquaculture expand worldwide. This robust, fast-growing species is favoured in the growing half-shell market and has replaced local native oyster species worldwide as the primary oyster species in culture. This global expansion has been met with the emergence of novel microvariants (μvars) of a virulent herpesvirus, the Ostreid herpesvirus 1 (OsHV-1). Industry important losses due to OsHV-1 μvars have initiated discussion of alternative species for aquaculture production, notably American oysters, Crassostrea virginica. Work to date has demonstrated that C. virginica is far less susceptible to OsHV-1 infection and pathology, but not immune. In this study, a viral pathogen transmission model describing disease impacts to mixed species aquaculture was developed in order to explore the influence of C. virginica introductions on OsHV-1 dynamics in existing C. gigas aquaculture systems. The model accounts for oyster filtration and release of viral particles from infected and dead individuals, and viral environmental decay. The model was verified and evaluated against real mortality data. For this, different aquaculture systems’ scenarios in terms of oyster species proportions were simulated: monoculture and 10/90, 40/60, and 50/50 co-culture systems. The  model performed adequately under varying species proportions, resulting in a promising tool for (i) improving the understanding of OsHV-1 – mixed oyster species system and providing insights into similar systems, and thus, (ii) potentially supporting studies about the influence of aquaculture species introduction on disease dynamics in existing aquaculture systems. Although more robust model validation is needed, the preliminary results of performed simulations here showed that the introductions of C. virginica in existing C. gigas aquaculture systems are not limiting disease progression: the co-culture scenarios did not confer a significant benefit to C. gigas.

Keywords: OsHV-1, C. virginica, C. gigas, model, co-culture