We have shown that mortalities due to OsHV-1 are strongly linked to water temperature. Observations of environmental conditions during outbreaks in affected estuaries in NSW since 2010 have now been confirmed under controlled laboratory conditions.
de Kantzow M, Hick P, Becker JA and Whittington RJ (2016). Effect of water temperature on mortality of Pacific oysters Crassostrea gigas associated with microvariant ostreid herpesvirus 1 (OsHV-1 μVar). Aquaculture Environment Interactions 8: 419-428.
Summary: The ostreid herpesvirus 1 microvariant (OsHV-1 μVar) causes mass mortality of Pacific oysters Crassostrea gigas. Water temperature can directly influence the incidence of disease or correlate with seasonal changes in the environment and oyster physiology that modify the susceptibility of the oysters to disease. The effect of water temperature was evaluated in controlled laboratory conditions by intramuscular injection of OsHV-1 μVar after acclimation of 8 mo old spat and 17 mo old adult oysters at 4 different temperatures (14, 18, 22 and 26°C). Mortality was 84 and 77% at 26 and 22°C, respectively, compared to 23% at 18°C and nil at 14°C. There was a statistically significant interaction between the dose of OsHV-1 μVar and water temperature. At 18°C, mortality occurred exclusively at a dose of 1 million OsHV-1 μVar genome copies per oyster whereas at the higher temperatures, oysters challenged with 1 thousand copies per oyster also died. Mortality did not occur at 14°C and OsHV-1 μVar was detected in tissues of only 1% of the oysters after 14 d. When accounting for temperature and dose, spat (8 mo) were 2.7 times more likely to die than adults (17 mo). Our study confirms a direct effect of water temperature on infection and disease caused by OsHV-1 μVar. We identified a threshold water temperature of between 14 and 18°C below which productive infection does not occur and the requirement for a higher dose of OsHV-1 μVar to initiate infection at 18°C than at 22°C. These results have implications for predicting and managing disease outbreaks caused by OsHV-1 μVar.
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