Effect of air exposure, handling stress and imidacloprid on the susceptibility of crassostrea gigas to ostreid herpesvirus 1 (OSHV-1)

Abstract

The emergence of the microvariant genotype of Ostreid herpesvirus 1 (OsHV-1 μVar) has caused mass mortalities of Pacific oysters Crassostrea gigas, resulting in significant economic losses in Europe, New Zealand and Australia. There is variability in the occurrence and severity of disease caused by OsHV-1, with the disease incompletely described by the known complex interactions between host, environment and pathogen. There is a need to evaluate the role of anthropogenic factors on this disease expression due to the number of interactions between humans and oysters. A controlled in vivo laboratory infection model was used to assess changes to the susceptibility of 6 mo old Pacific oysters to OsHV-1 challenge after pre-exposure to combinations of stressors. Pre-exposure of oysters to a concentration of the pesticide imidacloprid consistent with the higher range of environmental contamination in some estuaries had no impact on their survival or OsHV-1 viral load. Oysters pre-exposed to air for 24 h prior to OsHV-1 challenge by cohabitation were more resilient to infection. Moderate physical handling that simulated onfarm handling did not affect survival. This indicates that farm management practices implemented prior to OsHV-1 exposure might not specifically predispose oysters to more severe disease, and more complex confounding factors need to be considered. It is likely that changes in host physiology during emersion provide the host with increased resilience to disease caused by OsHV-1. Continued investigation of the effect of air exposure in the field will aid in validating the results from this laboratory experiment.