New Zealand juvenile oyster mortality associated with ostreid herpesvirus 1—an opportunistic longitudinal study

Abstract

During the 2010−11 summer outbreak of ostreid herpesvirus 1 (OsHV-1) in New Zealand, an opportunistic longitudinal field study was conducted. OsHV-1 PCR-negative oyster spat (Crassostrea gigas) were relocated to an OsHV-1 PCR-positive area of the North Island of New Zealand that was experiencing juvenile oyster mortalities. Over a period of 13 d, spat were monitored for mortality, sampled for histopathology, and tested for the presence of OsHV-1 using real time PCR and Vibrio culture. Histopathology showed some evidence of tissue pathology; however, no consistent progressive pathology was apparent. Field mortalities were evident from Day 6 on. After 5 and 7 d of exposure, 83 and 100% of spat, respectively, tested positive for the virus by real time PCR. Vibrio species recovered during the longitudinal study included V. splendidus and V. aestuarianus. This study offers insight into the rapidity of onset and virulence of the virus in naïve oyster spat in New Zealand waters. KEY WORDS: Ostreid herpesvirus 1 · Vibrio · Crassostrea gigas Resale or republication not permitted without written consent of the publisherDis Aquat Org 109: 231-239, 2014 al. 1972). In 1999, Le Deuff and Renault undertook initial molecular characterisation of the virus infecting Pacific oysters (Le Deuff & Renault 1999). This was followed up by the identification of the first variant (OsHV-1 Var) (Arzul et al. 2001a,b) and subsequent whole-genome sequencing of the ostreid herpesvirus 1 (OsHV-1; GenBank AY509253) (Davison et al. 2005). Segarra et al. (2010) published sequencing data on the emergence of the now problematic microvariant (OsHV-1 µVar).Several studies have identified other pathogens associated with major OsHV-1 mortality events in Europe. Vibrio species, including V. splendidus, V. aestuarianus and V. harveyi, have been isolated in association with OsHV-1 mortalities , Dégremont 2011, Schikorski et al. 2011a. Whilst Vibrio species are likely to be opportunistic pathogens, the significance of regular detection in association with OsHV-1 should not be overlooked. The major oyster mortality events in Europe are considered to be multi-factorial, with OsHV-1, Vibrio species and environmental conditions (e.g. increased water temperatures) all believed to contribute (Sauvage et al. 2009, Segarra et al. 2010, De Decker & Saulnier 2011, De Decker et al. 2011.During the summer of 2010−11 in New Zealand, OsHV-1, Vibrio species and warm water temperatures appeared to contribute to the deaths of juvenile C. gigas on the North Island of New Zealand. During the mortality event, the oyster industry provided access to pre-planned movements of apparently healthy hatchery-reared spat to an oyster growing site on the North Island where oyster mortalities attributed to OsHV-1 were occurring. This provided a unique opportunity to conduct a longitudinal study. This paper describes the molecular characterisation of the New Zealand OsHV-1 virus and results of the longitudinal study. MATERIALS AND METHODS Longitudinal studyApproximately 17 0...

In situ hybridization and histopathological observations during ostreid herpesvirus-1-associated mortalities in Pacific oysters Crassostrea gigas

“…Mortalities were estimated to range between 15 and 100% in spat and between 5 and 60% in adult oysters (Bingham et al 2013). The ostreid herpesvirus detected from affected oysters was similar to the microvariant genotype previously reported from the northern hemisphere (Keeling et al 2014). The OsHV-1 microvariant was detected from outbreaks of disease with unusually high mortalities in Pacific oyster spat and juveniles in France in 2008 (Segarra et al 2010.…”

“…As a result, OsHV-1 microvariants were detected by realtime PCR in 83% of spat by Day 5 following transfer from hatchery to a farm experiencing high level (up to 100%) mortalities in the farmed oysters (Keeling et al 2014). The aetiological role of OsHV-1 in the high losses experienced by the farm, while strongly suggested, was not fully established.…”

“…Resale or republication not permitted without written consent of the publisher dic losses experienced by oyster-producing regions in the USA, France, Spain, Ireland, Mexico, New Zealand and Australia (Friedman et al 2005, Vásquez-Yeomans et al 2010, Roque et al 2011, Jenkins et al 2013, Keeling et al 2014, Paul-Pont et al 2014 have been attributed to several OsHV-1 variants. The existence of many OsHV-1 genotypic variants may also reflect the wide natural host range of bivalves susceptible to infection with the virus (Hine & Thorne 1997, Hine et al 1998, Renault et al 2000, 2001, Arzul et al 2001a,b, Ren et al 2013.…”

“…For the development of the OsHV-1 ISH assay, formalin-fixed paraffin-embedded (FFPE) tissues that had been previously confirmed to be either positive (n = 4) or negative (n = 3) for OsHV-1 DNA by realtime PCR were used. To further investigate the involvement of OsHV-1 in the 2010−2011 summer mortality event in New Zealand, 87 FFPE tissue samples from live spat collected during the previous study (Keeling et al 2014) were examined ( Table 1). The FFPE tissues, approximately 2−5 mm thick, were obtained from a transverse cut between the labial palps and adductor muscle of the spat and processed as described previously (Keeling et al 2014).…”

Antiviral immunity in marine molluscs

“…These high mortalities were linked to the emergence of a newly described OsHV-1 genotype labelled mVar (Segarra et al, 2010). In addition, mortality events of Crassostrea gigas were reported in 2010 from New Zealand and Australia in association with a virus closely related to mVar (Jenkins et al, 2013;Keeling et al, 2014). Numerous genomic and proteomic studies investigating the host-pathogen interactions of Crassostrea gigas and OsHV-1 have been undertaken (Corporeau et al, 2014;Du et al, 2013;Fleury & Huvet, 2012;Green & Montagnani, 2013;Jouaux et al, 2013;Normand et al, 2014;Renault et al, 2011;Segarra et al, 2014a, b, c;Tamayo et al, 2014).…”