Need for improved biosecurity in oyster aquaculture.

Date: November 19, 2010

SCIENTIFIC OPINION
European Food Safety Authority (EFSA)

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.


Source: EFSA Panel on Animal Health and Welfare (2010). Scientific Opinion on the increased mortality events in Pacific oysters, Crassostrea gigas. EFSA Journal, 8(11):1894-1953.

ABSTRACT
In the summer of 2008 and 2009, severe mortality events in cultured Pacific oyster were reported from the main European producing countries. The European Commission requested EFSA to assess the relative importance of possible causes, including infectious agents with special focus on Ostreid herpesvirus 1 (OsHV-1) μvar and environmental factors. An assessment of the role of other mollusc species and the risks posed by transference of adult Pacific oysters from affected to unaffected areas was also requested. The available evidence suggests that OSHV-1 infection is a necessary cause but may not be a sufficient cause, the strain; OsHV-1 μvar seems to be dominant. An increase or a sudden change in the temperature was shown to be a risk factor. Husbandry practices such as introduction of non certified possibly infected spat, movements and mixing of populations and age groups are also important risk factors. In addition to C. gigas, there is evidence of susceptibility to OsHV-1 in Ostrea edulis, Pecten maximus and Ruditapes philippinarum.

It was concluded that it is not safe to transfer oysters older than 18 months from affected areas to areas not affected. The panel recommended that to promote and preserve a 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 and clear criteria for viral strain differentiation taking in account genotype and epidemiological criteria are necessary.

See http://www.efsa.europa.eu/en/scdocs/doc/s1894.pdf for summary (2 pg).
See http://www.efsa.europa.eu/en/scdocs/doc/1894.pdf for full report (59 pg).

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AquaVetMed e-News provides information to veterinary and veterinary-allied subscribers concerning aquatic animal medicine, health, welfare, public health and seafood safety, obtained from a variety of sources (largely AquaVetMed subscribers). While provided by the American Veterinary Medical Association's, Aquatic Veterinary Medicine Committee and are for public distribution, they do not necessarily reflect the opinion of the AVMA or the veterinary profession. See the AVMA Terms of Use (http://tinyurl.com/29h2rf) for further information.

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