Improved biosecurity in the oyster aquaculture industry in Europe urgently needed, EFSA report concludes
EFSA has published a scientific opinion on the risk factors linked to increased mortality among Pacific oysters in some Member States since 2008. The Panel on Animal Health and Welfare concluded that oysters older than 18 months can be a source of virus and it is not safe to transfer oysters older than 18 months from affected areas to areas not affected by increased mortality events.
The panel recommended that to best promote and preserve high health status and in particular to prevent and/or control increased mortality, measures are urgently needed to improve the general level of biosecurity in the oyster aquaculture industry in Europe. Furthermore to minimize the risk of subsequent transfer of infectious agents from hatcheries and wild- caught spat, there is a need to establish the health status of oyster spat at source. An assessment of the health status should include results of regular batch laboratory testing (at least in regards to OsHV-1, ref strain and µvar, Vibrio species, and histopathological examination) and epidemiological assessment.
Improved diagnostic methods should be developed to check for the presence of OsHV-1 µvar and other strains.The methods for detection of OsHV-1 (including different strains) need to be validated and harmonized. Relevant genomic information of the OsHV-1 µvar virus should be obtained for a better characterization of the strain in order to i) perform phylogenetic studies, ii) improve diagnosis iii) investigate potential for increased infectivity and virulence. The phylogenetic relationship of OsHV-1 strains should be investigated. Clear criteria for viral strain differentiation taking in account genotype and epidemiological criteria are necessary.
To better understand existing and emerging health problems, a robust health surveillance system for Pacific oyster production in Europe is needed. Well designed epidemiological research studies, including comparison studies, in order to determine the potential importance of infectious agents and other environmental factors on increased mortality in pacific oyster are necessary.