An investigation into the detection and identification of OsHV-1 μvar virus and associated risk factors causing mortalities in Crassostrea gigas in Ireland.

Abstract

Part two of this study investigated the detection of OsHV-1 μvar and associated risk factors during mortality outbreaks. An epidemiological study was conducted during 2011. 17 bays from around the Irish Coast were selected, comprising of sites which have been endemically infected by the OsHV-1 μVar virus. Batches of Pacific oysters, Crassostrea gigas were selected in each of the 17 bays and were tracked through the study period in an effort to identify any associated management factors. Samples of C. gigas oysters were collected from selected stocks in each of the 17 bays to screen for OsHV-1μvar. In addition to pathogen screening and tracking stocks of oysters, environmental monitoring also took place, using sampling points which were located in the vicinity of the point where the samples were collected. From the analysis of risk factors in 2011, several factors were found significant during mortality outbreaks, including hatchery source, and OsHV-1 viral load in 2011 and the maximum water temperature recorded between June and August 2011. Multivariable risk analysis indicated that mortalities increased with temperature until a peak was reached. The current study provides some insights into mortality events affecting farmed Pacific oyster production in Ireland. The epidemiological study conducted found that batch mortality was lower in 2011, compared with earlier years, in association with lower OsHV-1 μvar viral loads.