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Haematopoietic necrosis virus [cyprinid herpesvirus 2 (CyHV-2)] was isolated during disease outbreaks in goldfish, Carassius auratus, at an ornamental fish retail site in southern England in 2004. Signs of disease included lethargy and inappetence and were first seen after water temperatures increased from 14-15 to 19-21 degrees C. External gross pathology included pale patches on the gills and skin and internally the spleen was enlarged, often with distinctive white nodules. The most prominent histopathological changes observed were necrotic lesions in the spleen and kidney and focal patches of necrosis in the gill lamellae. Necrotic cells often contained nuclei with marginated chromatin and pale intranuclear inclusions. Ultrastructural examination of the spleen tissue revealed typical herpesvirus-like particles measuring 100 nm in diameter. The virus was isolated from extracts of gill tissue in KF-1 cells at 20 degrees C and oligonucleotide primer sets were designed based on conserved gene sequences and used to amplify viral DNA by polymerase chain reaction (PCR). The PCR assays were then used to detect the virus in DNA extracted from tissues sampled during earlier disease investigations at the retail site owner's holding facility in 2002 and 2003 and stored at -70 degrees C since then. Polymerase gene-specific PCR amplification products obtained from tissue samples and from the virus isolated in cell culture shared 100% nucleotide sequence identity with the published sequence for CyHV-2.

Cold water strawberry disease (CWSD), or red mark syndrome (RMS), is a severe dermatitis affecting the rainbow trout Oncorynchus mykiss. The condition, which presents as multifocal, raised lesions on the flanks of affected fish, was first diagnosed in Scotland in 2003 and has since spread to England and Wales. Results of field investigations indicated the condition had an infectious aetiology, with outbreaks in England linked to movements of live fish from affected sites in Scotland. Transmission trials confirmed these results, with 11 of 149 and 106 of 159 naïve rainbow trout displaying CWSD-characteristic lesions 104 to 106 d after being cohabited with CWSD-affected fish from 2 farms (Farm B from England and Farm C from Wales, respectively). The condition apparently has a long latency, with the first characteristic lesions in the previously naïve fish not definitively observed until 65 d (650 day-degrees) post-contact with affected fish. Affected fish from both outbreak investigations and the infection trial were examined for the presence of viruses, oomycetes, parasites and bacteria using a combination of techniques and methodologies (including culture-independent cloning of PCR-amplified bacterial 16S rRNA genes from lesions), with no potentially causative infectious agent consistently identified. The majority of the cloned phylotypes from both lesion and negative control skin samples were assigned to Acidovorax-like β-Proteobacteria and Methylobacterium-like α-Proteobacteria. KEY WORDS: RFLP · 16S rRNA · Clone library · Flavobacterium psychrophilum · Red mark syndromeResale or republication not permitted without written consent of the publisher Dis Aquat Org 79: 207-218, 2008 report that the disease is prevalent at low water temperatures (<15°C), in comparison to the UK experience of WWSD, which generally occurs only when water temperatures exceed 14°C (a summer rather than winter condition). Early signs of CWSD can include severe scale loss prior to the emergence of the characteristic external lesions (Ferguson et al. 2006), and there are no signs of systemic infection (i.e. no affect on appetite, growth or mortality). However, the condition causes losses to farmers both in treatment costs and in downgrading of affected fish at harvest.The objective of the present study was to determine if the disease had an infectious aetiology by conducting a disease investigation on farms affected by the condition. Laboratory trials evaluating whether the condition could be transmitted from affected to naïve fish were also conducted. As a recent report implicated Flavobacterium psychrophilum as potentially being linked to the condition (Ferguson et al. 2006), particular effort was made to identify whether this, or a closely related organism, was associated with diseased fish. MATERIALS AND METHODS Outbreak investigationsOutbreaks of CWSD at 3 farms in England and Wales were investigated between January 2005 and January 2006. Structured interviews with the farmers asked about the chronology of the disease o...

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There have been increased reports of outbreaks of enteric redmouth disease (ERM) caused by Yersinia ruckeri in previously vaccinated salmonids in Europe, with some of these outbreaks being attributed to emergent non-motile, Tween 80-negative, biotype 2 isolates. To gain information about their likely origins and relationships, a geographically and temporally diverse collection of isolates were characterised by serotyping, biotyping, pulsed-field gel electrophoresis (PFGE) and outer membrane protein (OMP) profiling. A total of 44 pulsotypes were identified from 160 isolates by PFGE, using the restriction enzyme Not I. Serotype O1 isolates responsible for ERM in rainbow trout in both the US and Europe, and including biotype 2 isolates, represented a distinct subgroup of similar pulsotypes. Biotype 2 isolates, responsible for outbreaks of the disease in rainbow trout in the UK, Denmark and Spain, had different pulsotypes, suggesting that they represented different clones that may have emerged separately. Danish biotype 2 isolates recovered since 1995 were indistinguishable by PFGE from the dominant biotype 1 clone responsible for the majority of outbreaks in Denmark and the rest of mainland Europe. In contrast, US biotype 2 isolate YRNC10 had an identical pulsotype and OMP profile to UK biotype 2 isolates, suggesting that there had been exchange of these isolates between the UK and the US in the past. UK Atlantic salmon isolates were genetically and serologically diverse, with 12 distinct pulsotypes identified among 32 isolates.KEY WORDS: Yersinia ruckeri · Pulsed-field gel electrophoresis · PFGE · Enteric redmouth disease · ERM · Biotype · Emerging strain Resale or republication not permitted without written consent of the publisherDis Aquat Org 84: [25][26][27][28][29][30][31][32][33] 2009 monovalent killed whole cell commercial vaccines, generally based on the Hagerman type strain (Horne & Barnes 1999). However, reports of ERM vaccine breakdown have emerged in Europe and the USA, which are attributed to biotype 2 (Tween 80-negative, nonmotile) isolates of Y. ruckeri (Austin et al. 2003, Fouz et al. 2006, Arias et al. 2007. Biotype 2 isolates were first described as having caused the disease in UK rainbow trout by Davies & Frerichs (1989).Farmers have also reported increasing mortalities due to yersiniosis of UK Atlantic salmon Salmo salar (L.); however, there are limited published studies regarding yersiniosis of this species (Bullock et al. 1976, Bruno & Munro 1989. Nevertheless, farmed Atlantic salmon fry in the major production areas of Europe (Scotland, Ireland and Norway) and Chile are routinely vaccinated with commercial rainbow trout ERM vaccines or autologous preparations (Bravo & Midtlyng 2007, L. A. Laidler pers. comm.). In Chile alone, up to 140 million salmon yr -1 were vaccinated against yersiniosis between and 2003(Bravo & Midtlyng 2007.Yersinia ruckeri is a highly clonal and biochemically homogeneous species (Schill et al. 1984, Stevenson & Airdrie 1984, Daly et al. 1986, Pyle et al...

Since its emergence in the 1990s, White Spot Disease (WSD) has had major economic and societal impact in the crustacean aquaculture sector. Over the years shrimp farming alone has experienced billion dollar losses through WSD. The disease is caused by the White Spot Syndrome Virus (WSSV), a large dsDNA virus and the only member of the Nimaviridae family. Susceptibility to WSSV in a wide range of crustacean hosts makes it a major risk factor in the translocation of live animals and in commodity products. Currently there are no effective treatments for this disease. Understanding the molecular basis of disease processes has contributed significantly to the treatment of many human and animal pathogens, and with a similar aim considerable efforts have been directed towards understanding host–pathogen molecular interactions for WSD. Work on the molecular mechanisms of pathogenesis in aquatic crustaceans has been restricted by a lack of sequenced and annotated genomes for host species. Nevertheless, some of the key host–pathogen interactions have been established: between viral envelope proteins and host cell receptors at initiation of infection, involvement of various immune system pathways in response to WSSV, and the roles of various host and virus miRNAs in mitigation or progression of disease. Despite these advances, many fundamental knowledge gaps remain; for example, the roles of the majority of WSSV proteins are still unknown. In this review we assess current knowledge of how WSSV infects and replicates in its host, and critique strategies for WSD treatment.

Microcell parasites have independently evolved in several eukaryotic lineages and are increasingly recognized as important and emerging pathogens of diverse hosts, including species of economic importance subject to international legislation concerning the trading of aquatic animals [1-3]. The microcell Mikrocytos mackini causes Denman Island disease of oysters and represents one of the most genetically divergent eukaryotes known. Mikrocytos has remained an isolated lineage with a limited distribution. We investigated two emerging diseases of juvenile crabs and oysters from the UK using massively parallel sequencing and targeted primer approaches to reveal that their causative agents are highly divergent lineages related to M. mackini (Paramikrocytos canceri n. gen. et n. sp. and M. mimicus sp. nov., respectively). We demonstrate a major new globally distributed parasite radiation (Mikrocytida ord. nov.) with phylogenetic affinities to the commercially important haplosporidian parasites of invertebrates. Mikrocytids have eluded detection because of their small size, intracellular habit, and extreme sequence divergence. P. canceri was frequently detected in a range of shoreline invertebrates, demonstrating that these newly recognized parasites are in fact common, diverse, and widespread and should be considered when assessing the risks of aquaculture activities, invasive species spread, and movements of ballast water and sediments with associated invertebrates.