Interaction between toxic dinoflagellate Alexandrium catenella exposure and disease associated with herpesvirus OsHV-1 μVar in Pacific oyster spat Crassostrea gigas

Blooms of toxic dinoflagellates can co-occur with mass mortality events associated with herpesvirus O5HV-1 mu Var infection that have been decimating Pacific oyster Crassostrea gigas spat and juveniles every summer since 2008 in France. This study investigated the possible effect of a harmful dinoflagellate, Alexandrium catenella, a producer of Paralytic Shellfish Toxins (PSTs), upon the oyster spat-herpesvirus interaction. Oyster spat from a hatchery were challenged by cohabitation with oysters contaminated in the field with O5HV-1 mu Var and possibly other pathogens. Simultaneously, the oysters were exposed to cultured A. catenella. Infection with O5HV-1 mu Var and PST accumulation were measured after 4 days of experimental exposure. Exposure to Alexandrium catenella modified the host-pathogen interaction by reducing prevalence of O5HV-1 mu Var infection. In addition, oysters challenged with OsHV-1 mu Var and possibly other pathogens from the environment accumulated smaller amounts of PSTs than unchallenged oysters. Three possible mechanisms are suggested by these results: (i) possible direct interactions between A. catenella and herpesvirus (or associated pathogens) could reduce viral transmission and algal availability for oyster consumption; (ii) oyster feeding behavior or digestive functions may have been altered, thus decreasing both uptake of viral particles and consumption or digestion of toxic algae and consequent toxin accumulation; (iii) immuno-activation by A. catenella could enhance defense efficiency against O5HV-1 mu Var infection. These findings suggest further research on relationships between O5HV-1 mu Var and toxic dinoflagellates and their combined effects upon disease transmission and proliferation processes, as well as on oyster physiological and immunological involvement in this complex, tripartite interaction. (C) 2015 Elsevier B.V. All rights reserved.