Mass mortality of farmed Pacific oysters Crassostrea gigas caused by Ostreid herpesvirus-1 is an international problem that has been linked to warm water temperatures. However, little is known about the environmental conditions leading up to the first appearance of the disease in a region – this is called an index case. Our aim was to look for consistent environmental features between the four index cases in Australia that occurred between 2010 and 2024. Water temperature alone did not explain these index cases but each one was preceded by unusually low rainfall and higher rates of temperature change that may be proxies for a range of undetermined factors. Comprehensive protocols for data acquisition are needed during future index cases.
Whittington RJ, Ingram L and Rubio A (2024). Environmental conditions associated with four index cases of Pacific oyster mortality syndrome (POMS) in Crassostrea gigas in Australia between 2010 and 2024: emergence or introduction of Ostreid herpesvirus-1? Animals 14 (Issue 21) 3052. doi:10.3390/ani14213052
Summary: Warm water temperature is a risk factor for recurrent mass mortality in farmed Pacific oysters Crassostrea gigas caused by Ostreid herpesvirus-1, but there is little information on environmental conditions when the disease first appears in a region – the index case. Environmental conditions between four index cases in Australia (2010, 2013, 2016 and 2024) were compared to provide insight into possible origins of the virus. Each index case was preceded by unusually low rainfall and higher rates of temperature change that could increase oyster susceptibility through thermal flux stress. Water temperature alone did not explain the index cases, there being no consistency in sea surface, estuary or air temperatures between them. Tidal cycles and chlorophyll-a levels were unremarkable, harmful algae were present in all index cases and anthropogenic environmental contamination was unlikely. The lack of an interpretable change in the estuarine environment suggests recent introduction of OsHV-1, however viral emergence from a local reservoir cannot be excluded. Future events will be difficult to predict. Temperature flux and rainfall are likely important, but they are proxies for a range of undetermined factors and to identify these, it will be necessary to develop comprehensive protocols for data acquisition during future index cases.
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