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...

Yersinia ruckeri is a salmonid pathogen with widespread distribution in cool-temperate waters including Australia and New Zealand, two isolated environments with recently developed salmonid farming industries. Phylogenetic comparison of 58 isolates from Australia, New Zealand, USA, Chile, Finland and China based on non-recombinant core genome SNPs revealed multiple deep-branching lineages, with a most recent common ancestor estimated at 18 500 years BP (12 355–24 757 95% HPD) and evidence of Australasian endemism. Evolution within the Tasmanian Atlantic salmon serotype O1b lineage has been slow, with 63 SNPs describing the variance over 27 years. Isolates from the prevailing lineage are poorly/non-motile compared to a lineage pre-vaccination, introduced in 1997, which is highly motile but has not been isolated since from epizootics. A non-motile phenotype has arisen independently in Tasmania compared to Europe and USA through a frameshift in fliI, encoding the ATPase of the flagella cluster. We report for the first time lipopolysaccharide O-antigen serotype O2 isolates in Tasmania. This phenotype results from deletion of the O-antigen cluster and consequent loss of high-molecular-weight O-antigen. This phenomenon has occurred independently on three occasions on three continents (Australasia, North America and Asia) as O2 isolates from the USA, China and Tasmania share the O-antigen deletion but occupy distant lineages. Despite the European and North American origins of the Australasian salmonid stocks, the lineages of Y. ruckeri in Australia and New Zealand are distinct from those of the northern hemisphere, suggesting they are pre-existing ancient strains that have emerged and evolved with the introduction of susceptible hosts following European colonization.

A real-time PCR assay using a molecular beacon was developed and validated to detect the vapA (surface array protein) gene in the fish pathogen, Aeromonas salmonicida. The assay had 100% analytical specificity and analytical sensitivities of 5 ± 0 fg (DNA), 2.2 × 10(4) ± 1 × 10(4) CFU g(-1) (without enrichment) and 40 ± 10 CFU g(-1) (with enrichment) in kidney tissue. The assay was highly repeatable and proved to be robust following equivalency testing using a different real-time PCR platform. Following analytical validation, diagnostic specificity was determined using New Zealand farmed Chinook salmon, Oncorhynchus tshawytscha (Walbaum), (n = 750) and pink shubunkin, Carassius auratus (L.) (n = 157). The real-time PCR was run in parallel with culture and all fish tested were found to be negative by both methods for A. salmonicida, resulting in 100% diagnostic specificity (95% confidence interval). The molecular beacon real-time PCR system is specific, sensitive and a reproducible method for the detection of A. salmonicida. It can be used for diagnostic testing, health certification and active surveillance programmes.

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A total of 777 fish from three growing regions of New Zealand Chinook salmon farms comprising of five sites were tested. Quantitative PCR was used to determine the distribution of New Zealand rickettsia‐like organism and Tenacibaculum maritimum. Genetic information from these bacteria were then compared with strains reported worldwide. Using this information, suggested associations of pathogens with clinically affected fish were made. NZ‐RLO was detected in two of the three regions, and T. maritimum was detected in all regions. Three strains of NZ‐RLO were identified during this study. Based on analysis of the ITS rRNA gene, NZ‐RLO1 appears to be part of an Australasian grouping sharing high similarity with the Tasmanian RLO, NZ‐RLO2 was shown to be the same as an Irish strain, and NZ‐RLO3 was shown be closely related to two strains from Chile. Based on multi‐locus sequence typing, the New Zealand T. maritimum was the same as Australian strains. NZ‐RLOs were detected more frequently in fish with skin ulcers than fish without skin ulcers. While additional research is required to investigate the pathogenicity of these organisms, this is the first time that NZ‐RLOs have been associated with the development of clinical infections in farmed Chinook salmon.