Oyster mortality

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Article
Pacific oyster; mortality; Crassostrea gigas; ostreid herpesvirus; Vibrio aestuarianus
First published in the EFSA Journal
4 June 2015
Adopted
5 May 2015
Type
Scientific Opinion
Abstract

This updated scientific opinion on oyster mortality addresses 1) the role of ostreid herpesvirus (OsHV-1) in mortality, 2) evidence for a role of Vibrio aestuarianus in mortality, 3) effectiveness of water treatment in inactivating OsHV-1 and V. aestuarianus and 4) feasibility, availability and effectiveness of the disease prevention and control measures. A new pattern of mass mortality of Pacific oysters (C. gigas) was observed in France and other European countries from 2008 onwards. Similar outbreaks were reported in 2010-11 from Australia and New Zealand. Studies performed since 2010 has provided strong evidence that OsHV-1 µVar is causally linked to increased oyster spat mortality at sea water temperatures above 16 °C. V. aestuarianus subsp. francensis was detected in France in 2001 in moribund oysters; since then this bacterium has been regularly detected during oyster mortality events. Owing to a lack of information, the causal relationship between V. aestuarianus and oyster mortality has not been established. Discharge of untreated seawater from depuration plants remains a potential mode of transmission of diseases affecting bivalves and other marine life. Effective disinfection of seawater effluent from depuration and holding facilities will minimize the risk of transmission of infectious agents. Unrestricted movement of oysters is associated with a high risk of spread of OsHV-1. Wild populations of C. gigas also contribute to spread of OsHV-1. Only a few areas in Europe continue to remain free from OsHV-1. Once infected, an area is not likely to regain freedom from OsHV-1 if a wild population of C. gigas is present. Almost all OsHV-1 strains isolated after 2008 conform to the definition of microvariants. Therefore, it appears unnecessary to maintain a separate definition of microvariants for disease control purposes. The criteria in Directive 2006/88/EC for listing of non-exotic diseases are currently not fulfilled for mortality caused by OsHV-1 microvariants.

Panel members at the time of adoption
Charlotte Berg, Anette Bøtner, Howard Browman, Aline De Koeijer, Klaus Depner, Mariano Domingo, Christian Ducrot, Sandra Edwards, Christine Fourichon, Frank Koenen, Simon More, Mohan Raj, Liisa Sihvonen, Hans Spoolder, Jan Arend Stegeman, Hans-Hermann Thulke, Ivar Vågsholm, Antonio Velarde and Preben Willeberg
Panel on Animal Health and Welfare
Contact
alpha [at] efsa.europa.eu
doi
10.2903/j.efsa.2015.4122
EFSA Journal 2015;13(6):4122 [59 pp.].
Question Number
On request from
European Commission
Print on demand
Number of Pages
59