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Piscirickettsia salmonis is the causative agent of piscirickettsiosis, a disease with high socio-economic impacts for Chilean salmonid aquaculture. The identification of major environmental reservoirs for P. salmonis has long been ignored. Most microbial life occurs in biofilms, with possible implications in disease outbreaks as pathogen seed banks. Herein, we report on an in vitro analysis of biofilm formation by P. salmonis Psal-103 (LF-89-like genotype) and Psal-104 (EM-90-like genotype), the aim of which was to gain new insights into the ecological role of biofilms using multiple approaches. The cytotoxic response of the salmon head kidney cell line to P. salmonis showed interisolate differences, depending on the source of the bacterial inoculum (biofilm or planktonic). Biofilm formation showed a variable-length lag-phase, which was associated with wider fluctuations in biofilm viability. Interisolate differences in the lag phase emerged regardless of the nutritional content of the medium, but both isolates formed mature biofilms from 288 h onwards. Psal-103 biofilms were sensitive to Atlantic salmon skin mucus during early formation, whereas Psal-104 biofilms were more tolerant. The ability of P. salmonis to form viable and mucus-tolerant biofilms on plastic surfaces in seawater represents a potentially important environmental risk for the persistence and dissemination of piscirickettsiosis. [ABSTRACT FROM AUTHOR]

Abstract Proliferative kidney disease (PKD) of salmonids is a disease of economic and environmental concern caused by the myxozoan parasite Tetracapsuloides bryosalmonae. Finer details of the immune repertoire during T. bryosalmonae infection have been elucidated in rainbow trout (Oncorhynchus mykiss). In contrast, there remain many unanswered questions regarding the immune response of the wild fish host in Europe, the brown trout (Salmo trutta) to this parasite. The first aim of this study is to examine the brown trout immune response to T. bryosalmonae and compare it with the published information on rainbow trout as two species that have undergone a different coevolution with the parasite. According to ecoimmunology terminology, infected organisms may manage infection by reducing the damage caused by parasites (tolerance) or by limiting parasite burden (resistance). The second aim of this study is to investigate tolerance/resistance patterns of these species during PKD infection. Our results suggest subtle differences in sequential aspects of the immune response and of immune genes that correlate with parasite intensity for the brown trout, in contrast to rainbow trout, in terms of the B cell response and Th-like interplay that may be linked to PKD pathogenesis. These differences in the immune response also correlate with species-specific differences in tolerance/resistance patterns, in that brown trout had increased tolerance but rainbow trout had greater resistance to infection. The variance in tolerance/resistance investment resulted in a different evolutionary outcome for each host-parasite interaction. A greater exploration of these concepts and an association of immune mechanisms could open an additional gateway for interpreting fish host-parasite interactions. Highlights • We assessed the immune response of brown trout to Tetracapsuloides bryosalmonae. • Combinatorial B cell gene profiling indicated a strong antibody type response. • Th1-like cytokines (Tbet, IFNγ and TNFα) were upregulated at later time points. • We compared tolerance/resistance defence strategies in two salmonids. • Brown trout had increased tolerance, but rainbow trout had greater resistance. [ABSTRACT FROM AUTHOR]

Many rivers in the Pacific Northwest region of North America are anthropogenically manipulated via dam operations, leading to system-wide impacts on hydrodynamic conditions and aquatic communities. Understanding how dam operations alter abiotic and biotic variables is important for designing management actions. For example, in the Klamath River, dam outflows could be manipulated to alter water age and temperature to reduce risk of parasite infections in salmon by diluting or altering viability of parasite spores. However, sensitivity of water age and temperature to the riverine conditions such as bathymetry can affect outcomes from dam operations. To examine this issue in detail, we conducted a global sensitivity analysis of water age and temperature to a comprehensive set of hydraulics and meteorological parameters in the Klamath River, California, where management of salmonid disease is a high priority. We applied an analysis technique, which combined Latin-hypercube and one-at-a-time sampling methods, and included simulation runs with the hydrodynamic numerical model of the Lower Klamath. We found that flow rate and bottom roughness were the two most important parameters that influence water age. Water temperature was more sensitive to inflow temperature, air temperature, solar radiation, wind speed, flow rate, and wet bulb temperature respectively. Our results are relevant for managers because they provide a framework for predicting how water within ‘high infection risk’ sections of the river will respond to dam water (low infection risk) input. Moreover, these data will be useful for prioritizing the use of water age (dilution) versus temperature (spore viability) under certain contexts when considering flow manipulation as a method to reduce risk of infection and disease in Klamath River salmon. [ABSTRACT FROM AUTHOR]

While intensive fish production has many advantages, it also has a number of drawbacks as regards disease and stress. To date, there has been no conclusive review of disease resistance at Czech fish farms. The aim of the study was to describe briefly the existing salmonid breeding practice in the Czech Republic and to point out the trends and new possibilities gaining ground around Europe. However, the present situation in the Czech stocks is not rare at all and therefore it is used here as a model example representing numerous breeding practices in Europe. Stress and disease resistance in fish is polygenic and quantitative, making selection for such traits difficult. In recent years, however, fish breeding methods have developed rapidly, with the use of genetic analysis tools, for example, now allowing much greater selection accuracy. Gradual progress in understanding the importance of individual genetic markers offers many new options that can be utilised in breeding practice. New selection methods, such as quantitative trait loci (QTLs) and genomic selection, are increasingly employed in European aquaculture. Next generation sequencing techniques now help in the finding of new and promising QTLs that can be used in assisted selection. This review maps the current progress in improving salmonid resistance to stress and disease in aquaculture and at the same time provides the breeders with a short overview of the latest tools of genetically controlled breeding and of the newest products available at the European market. [ABSTRACT FROM AUTHOR]

Salmonid alphavirus (SAV), genus Alphavirus, family Togaviridae, is a single-stranded RNA virus affecting Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). It is known to be responsible for pancreas disease (PD) and sleeping disease (SD) which are increasing problems, causing high fish mortality and economic losses in the European aquaculture industry. Pancreas disease was first described in Atlantic salmon in Scotland in 1976 and a similar disease caused by the closely related sleeping disease virus was first described in rainbow trout in France. There have also been reports of salmonid alphavirus infections from other European countries, including Ireland, England, Norway, Germany, Italy, and Spain. Salmonid alphaviruses have been classified into six subtypes (SAV1-6). SAV1 and SAV4-6 cause pancreas disease in Atlantic salmon in Ireland or Scotland, SAV2 is the causative agent of sleeping disease in rainbow trout, and SAV3 has been detected in Atlantic salmon in Norway. The aim of this paper was to summarise current knowledge of infections caused by salmonid alphavirus and diagnostic methods including the newest techniques, and to briefly describe prevention from SAV infections by vaccination. [ABSTRACT FROM AUTHOR]

Abstract: Proliferative kidney disease (PKD) of salmonids caused by Tetracapsuloides bryosalmonae causes high mortalities of wild brown trout (Salmo trutta fario) and farmed rainbow trout (Oncorhynchus mykiss) at elevated water temperatures. Here the aim was to compare the temperature‐dependent modulation of T. bryosalmonae in the two salmonid host species, which display different temperature optima. We used a novel experimental set‐up in which we exposed brown trout and rainbow trout to an identical quantified low concentration of T. bryosalmonae for a short time period (1 hr). We followed the development of the parasite in the fish hosts for 70 days. PKD prevalence and parasite kinetics were assessed using qPCR. Exposures were performed at temperatures (12°C and 15°C) that reflect an environmental scenario that may occur in the natural habitat of salmonids. T. bryosalmonae infection was confirmed earliest in brown trout kept at 15°C (day 7 post‐exposure) while, in all other groups, T. bryosalmonae was not confirmed until day 15 post‐exposure. Moreover, significantly greater infection prevalence and a faster increase of parasite intensity were observed in brown trout kept at 15°C than in all other groups. These results indicate that PKD is differentially modulated by water temperature in related host species. [ABSTRACT FROM AUTHOR]

This work reports the effect of two DNA vaccines against salmonid alphavirus 3 ( SAV3) in Atlantic salmon. Presmolts were vaccinated by intramuscular injection of plasmids encoding the SAV3 structural polyprotein C-E3-E2-6K-E2 ( pCSP), E2 only ( pE2), or plasmid without insert (pc DNA3.3). E2 is expressed at the surface of cells transfected with pCSP and internally in cells transfected with pE2. A commercial vaccine based on inactivated SAV ( NCPD) was used for comparison. At 10 weeks post-vaccination, only fish vaccinated with pCSP showed antibody against E2 and virus-neutralizing activity. Vaccinated fish were infected with SAV3 to determine protection by virus quantitation in serum after 7 days and scoring of pathological changes after 21 days. Fish vaccinated with both pCSP and NCPD vaccines showed significant virus reduction in serum, while fish vaccinated with pE2 did not. All fish vaccinated with pc DNA3.3 and pE2 showed pathological changes in organs typical of PD, 60% of fish vaccinated with NCPD showed PD pathology, while fish vaccinated with pCSP did not show PD pathology. Taken together, DNA vaccination with pCSP provided strong protection for salmon against SAV3 infection, which in part may be due to production of virus-neutralizing antibodies. [ABSTRACT FROM AUTHOR]

Infections caused by the facultative intracellular bacterial pathogen Piscirickettsia salmonis remains an unsolved problem for the aquaculture as no efficient treatments have been developed. As a result, substantial amounts of antibiotic have been used to limit salmonid rickettsial septicemia (SRS) disease outbreaks. The antibiotic usage has not reduced the occurrence, but lead to an increase in resistant strains, underlining the need for new treatment strategies. P. salmonis produce membrane vesicles (MVs); small spherical structures know to contain a variety of bacterial components, including proteins, lipopolysaccharides (LPS), DNA and RNA. MVs mimics' in many aspects their mother cell, and has been reported as alternative vaccine candidates. Here, MVs from P. salmonis was isolated and evaluated as a vaccine candidate against SRS in an adult zebrafish infection model. When zebrafish was immunized with MVs they were protected from subsequent challenge with a lethal dose of P. salmonis . Histological analysis showed a reduced bacterial load upon challenge in the MV immunized group, and the mRNA expression levels of several immune related genes altered, including mpeg1.1, tnfα , il1b, il10 and il6 . The MVs induced the secretion of IgM upon immunization, indicating an immunogenic effect of the vesicles. Taken together, the data demonstrate a vaccine potential of MVs against P. salmonis. [ABSTRACT FROM AUTHOR]

A new disease in farmed rainbow trout (Onchorhyncus mykiss) was described in Norway in 2013. The disease mainly affected the heart and resembled heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar L.). HSMI is associated with Piscine orthoreovirus (PRV), and a search for a similar virus in the diseased rainbow trout led to detection of a sequence with 85% similarity to PRV. This finding called for a targeted effort to assess the risk the new PRV-variant pose on farmed rainbow trout and Atlantic salmon by studying infection and disease pathogenesis, aiming to provide more diagnostic knowledge. Based on the genetic relationship to PRV, the novel virus is referred to as PRV-Oncorhynchus mykiss (PRV-Om) in contrast to PRV-Salmo salar (PRV-Ss). In experimental trials, intraperitoneally injected PRV-Om was shown to replicate in blood in both salmonid species, but more effectively in rainbow trout. In rainbow trout, the virus levels peaked in blood and heart of cohabitants 6 weeks post challenge, along with increased expression of antiviral genes (Mx and viperin) in the spleen, with 80–100% of the cohabitants infected. Heart inflammation was diagnosed in all cohabitants examined 8 weeks post challenge. In contrast, less than 50% of the Atlantic salmon cohabitants were infected between 8 and 16 weeks post challenge and the antiviral response in these fish was very low. From 12 weeks post challenge and onwards, mild focal myocarditis was demonstrated in a few virus-positive salmon. In conclusion, PRV-Om infects both salmonid species, but faster transmission, more notable antiviral response and more prominent heart pathology were observed in rainbow trout. [ABSTRACT FROM AUTHOR]

This paper presents a validated protocol, using a novel, specifically formulated medium, to perform broth microdilution antimicrobial susceptibility assays of the salmonid bacterial pathogen Piscirickettsia salmonis. The minimum inhibitory concentrations (MIC) for florfenicol and oxytetracycline against 58 P. salmonis isolates recovered from various outbreaks occurred in Chilean salmonid farms were determined using this protocol. Normalized resistance interpretation (NRI) analysis was applied to these data to calculate appropriate protocol-specific epidemiological cut-off values. These cut-off values allow the isolates to be categorized as either fully susceptible wild type (WT) members of this species, or as manifesting reduced susceptibility non-wild type (NWT). The distribution of MIC values of florfenicol was bimodal and the distribution of the normalized values for the putative WT observation had a standard deviation of 0.896 log2 mg mL-1. This analysis calculated a cut-off value of ≤0.25 mg mL-1 and categorized 33 (56%) of the isolates as manifesting reduced susceptibility to florfenicol. For the oxytetracycline MIC data the NRI analysis also treated the distribution as bimodal. The distribution of the normalized values for the putative WT observation had a standard deviation of 0.951 log2 mg mL-1. This analysis gave a cut-off value of ≤0.5 mg mL-1 and categorized five isolates (9%) as manifesting reduced susceptibility to oxytetracycline. The susceptibility testing protocol developed in this study was capable of generating MIC data from all the isolates tested. On the basis of the precision of the data it generated, and the degree of separation of values for WT and NWT it achieved, it is argued that this protocol has the performance characteristics necessary for it to be considered as a standard protocol. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is an important pathogen of salmonid fishes. A validated universal reverse transcriptase quantitative PCR (RT-qPCR) assay that can quantify levels of IHNV in fish tissues has been previously reported. In the present study, we adapted the published set of IHNV primers and probe for use in a reverse-transcriptase droplet digital PCR (RT-ddPCR) assay for quantification of the virus in fish tissue samples. The RT-ddPCR and RT-qPCR assays detected 13 phylogenetically diverse IHNV strains, but neither assay produced detectable amplification when RNA from other fish viruses was used. The RT-ddPCR assay had a limit of detection (LOD) equating to 2.2 plaque forming units (PFU)/μl while the LOD for the RT-qPCR was 0.2 PFU/μl. Good agreement (69.4–100%) between assays was observed when used to detect IHNV RNA in cell culture supernatant and tissues from IHNV infected rainbow trout ( Oncorhynchus mykiss ) and arctic char ( Salvelinus alpinus ). Estimates of RNA copy number produced by the two assays were significantly correlated but the RT-qPCR consistently produced higher estimates than the RT-ddPCR. The analytical properties of the N gene RT-ddPCR test indicated that this method may be useful to assess IHNV RNA copy number for research and diagnostic purposes. Future work is needed to establish the within and between laboratory diagnostic performance of the RT-ddPCR assay. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV) is a common pathogen that causes severe disease in the salmonid aquaculture industry. Because oral vaccines induce more efficient mucosal immunity than parenteral immunization, an oral vaccine was developed with an improved yeast cell surface display technology to induce an immune response to IHNV. The oral yeast vaccine, designated EBY100/pYD1-bi-G, was delivered orally to rainbow trout ( Oncorhynchus mykiss ) on days 1 and 32, and the nonspecific and specific immune responses were measured 50 days after the first vaccination. In the hindgut, spleen, and head kidney, the expression of IFN-1 and Mx-1 was significantly upregulated after oral vaccination with EBY100/pYD1-bi-G, and the highest expression of IFN-1 and Mx-1 was observed in the spleen (7.5-fold higher than the control group) and head kidney (3.9-fold higher than the control group), respectively. Several markers of the adaptive immune response (IgM, IgT, CD4, and CD8) were also significantly upregulated, and the highest expression of these markers was observed in the hindgut, suggesting that the mucosal immune response was successfully induced by oral vaccination with EBY100/pYD1-bi-G. Sera from the orally vaccinated rainbow trout showed higher anti-IHNV neutralizing antibody titers (antibody titer 81 ± 4) than the control sera (antibody titer 7 ± 3), and the relative percentage survival after IHNV challenge was 45.8% compared with 2% in the control group. Although the protection afforded by this orally delivered vaccine was lower than that of a DNA vaccine (83%–98%), it is a promising candidate vaccine with which to protect larval fish against IHNV, which are most susceptible to the virus and difficult to inject with a DNA vaccine. [ABSTRACT FROM AUTHOR]

Fredericella sultana is an invertebrate host of Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease in salmonids. The bryozoan produces seed-like statoblasts to facilitate its persistence during unfavourable conditions. Statoblasts from infected bryozoans can harbor T. bryosalmonae and give rise to infected bryozoan colonies when conditions improve. We aimed in the present study to evaluate the integrity and viability of T. bryosalmonae-infected statoblasts after a range of harsh treatment conditions. We tested if statoblasts could survive ingestion by either brown trout or common carp. After ingestion, the fish faeces was collected at different time points. We also tested physical stressors: statoblasts collected from infected colonies were desiccated at room temperature, or frozen with and without Bryozoan Medium C (BMC). After treatments, statoblasts were assessed for physical integrity before being incubated on BMC to allow them to hatch. After 4 weeks, hatched and unhatched statoblasts were tested by PCR for the presence of the parasite. We found that statoblasts ingested by brown trout and those frozen in BMC were completely broken. In contrast, statoblasts ingested by common carp and those subjected to dry freezing were able to survive and hatch. T. bryosalmonae was detected by PCR in both hatched and unhatched infected statoblasts, but neither from broken nor uninfected statoblasts. Our results confirmed for the first time the ability of infected statoblasts to survive passage through a fish, and freezing. These findings suggest potential pathways for both persistence and spread of T. bryosalmonae-infected statoblasts in natural aquatic systems. [ABSTRACT FROM AUTHOR]

The article presents a study of the specificity and sensitivity of real time reverse-transcriptase polymerase chain reaction (RC-PCR) with universal probe library (UPL) for the diagnosis of infectious pancreatic necrosis virus (IPNV) through genogroups 1 and 5 in salmonid tissues. Results demonstrated the high potential of RT-PCR with UPL probes for early IPNV diagnosis with positive health and economic impact in the salmonid industry.

Interactions among host, microbiota and viral pathogens are complex and poorly understood. The goal of the present study is to assess the changes in the skin microbial community of Atlantic salmon (Salmo salar L.) in response to experimental infection with salmonid alphavirus (SAV). The salmon skin microbial community was determined using 16S rDNA pyrosequencing in five different experimental groups: control, 7 days after infection with low-dose SAV, 14 days after infection with low-dose SAV, 7 days after infection with high-dose SAV, and 14 days after infection with high-dose SAV. Both infection treatment and time after infection were strong predictors of the skin microbial community composition. Skin samples from SAV3 infected fish showed an unbalanced microbiota characterized by a decreased abundance of Proteobacteria such as Oleispira sp. and increased abundances of opportunistic taxa including Flavobacteriaceae, Streptococcaceae and Tenacibaculum sp. These results demonstrate that viral infections can result in skin dysbiosis likely rendering the host more susceptible to secondary bacterial infections. [ABSTRACT FROM AUTHOR]

Flavobacterium psychrophilum is one of the most important bacterial pathogens affecting cultured rainbow trout ( Oncorhynchus mykiss ) and is increasingly causing problems in Atlantic salmon ( Salmo salar L.) hatcheries. Little is known about the heterogeneity of F. psychrophilum isolates on UK salmonid farms. A total of 315 F. psychrophilum isolates, 293 of which were collected from 27 sites within the UK, were characterised using four genotyping methods and a serotyping scheme. A high strain diversity was identified among the isolates with 54 pulsotypes, ten (GTG) 5 -PCR types, two 16S rRNA allele lineages, seven plasmid profiles and three serotypes. Seven PFGE groups and 27 singletons were formed at a band similarity of 80%. PFGE group P (n = 75) was found to be numerically predominant in eight sites within the UK. Two major PFGE clusters and 13 outliers were found at the band similarity of 40%. The predominant profileobserved within the F. psychrophilum isolates examined was PFGE cluster II − (GTG) 5 -PCR type r1–16S rRNA lineage II − serotype Th (70/156 isolates examined, 45%). Co-existence of genetically and serologically heterogeneous isolates within each farm was detected, confounding the ability to control RTFS outbreaks. The occurrence over time (up to 11 years) of F. psychrophilum pulsotypes in three representative sites (Scot I, Scot III and Scot V) within Scotland was examined, potentially providing important epidemiological data for farm management and the development of site-specific vaccines. [ABSTRACT FROM AUTHOR]

Parasites and pathogens can have an important effect on their host's thermal resistance. The impact of parasite infection on host physiological performances has traditionally been studied in controlled laboratory conditions, and much less is known about its actual effects in wild populations. Nonetheless, such knowledge is critical when assessing the effect of climate change on the future survival of the host., Tetracapsuloides bryosalmonae is a myxozoan endoparasite causing proliferative kidney disease (PKD) in salmonids. Infection and clinical symptoms of PKD are dependent on environmental temperature and PKD has become an emerging disease of primary importance for farmed and wild salmonids in the last decades. Despite important achievements in understanding PKD pathology in recent years, there are still crucial gaps in the knowledge of the disease ecology, notably in how the parasite affects host performance in the wild., We sampled juvenile (0+) brown trout ( Salmo trutta) from the wild during early and late summer and assessed relative parasite load (DNA quantification with qPCR) and disease severity (kidney hyperplasia). We also measured haematocrit, leucocyte formula, aerobic scope and upper thermal tolerance in a field-physiology approach in order to better understand the relationships between PKD severity and host performance. By using wild-caught individuals and performing measurements directly on location, we aimed to gain insights into host physiology in a natural environment while avoiding biases caused by laboratory acclimation., We found that most physiopathological symptoms in the wild were strongly correlated with kidney hyperplasia, but more weakly linked to parasite load. Disease severity was positively correlated with anaemia and abundance of circulating thrombocytes, and negatively correlated with aerobic scope and thermal tolerance., Our results suggest that impaired aerobic performances and thermal tolerance in infected fish may potentially result in decreased host survival in the wild, especially in relation with predicted higher average summer temperatures and increased frequency of extreme events (summer heatwaves) in the context of global climate change., A is available for this article. [ABSTRACT FROM AUTHOR]

Infectious hematopoietic necrosis virus (IHNV; n = 18) was identified in the Korean national surveillance program between February 2013 and April 2015, suggesting that IHNV is a major viral pathogen in cultured salmonids. By phylogeny analysis, we found that the JRt-Nagano and JRt-Shizuoka groups could each be further subdivided into three distinct subtypes. The Korean strains were genetically similar to Japanese isolates, suggesting introduction from Japan. Interestingly, the amino acid sequences of the middle glycoprotein gene show that distinct Korean subtypes have circulated, indicating that the settled IHNVs might be evolved stably in cultured salmonid farm environments. [ABSTRACT FROM AUTHOR]

Amoebic gill disease (AGD), first documented thirty years ago in sea-caged salmonids, is an ever increasing global concern in finfish aquaculture. The result of gill infection by Neoparamoeba perurans , clinical AGD has been observed in fourteen countries distributed across six continents and in fifteen species of finfish. The greatest impacts of AGD have been on farmed Atlantic salmon during the seawater grow-out phase. When left untreated AGD has resulted in up to 80% mortality, and even mild infections reduce production performance and fish welfare. This review summarizes and analyses three decades of AGD research and outbreaks, with focus on the causal triad of pathogen, host and environment. Statement of relevance This review provides an improved understanding of AGD including practical applications. [ABSTRACT FROM AUTHOR]

Sea lice are the most damaging parasite of marine salmonids, both economically and in terms of potential impacts on wild fish. An increasingly widely applied control is the use of cleaner fish ( CF) such as wrasse that eat lice. However, such CF can carry pathogens that may cause disease in salmon, including the potential emergence of new diseases. This is not just a theoretical risk, as demonstrated by a recent outbreak of viral haemorrhagic septicaemia in wrasse held on salmon farms in Shetland. A modelling framework is developed to identify conditions in which emergence might occur, and, from this, means of reducing risk. Diseases that might emerge easily in farmed salmon would be likely to have already done so by other routes of exposure, and if risks are very low, they would need to be greatly enhanced to become significant relative to costs of lice control. CF may most enhance risks from disease with moderate probability of emerging. Risks of emergence can be reduced by replacing wild-caught with hatchery-reared CF, minimizing mixing of CF from different sources, surveillance for clinical disease in the CF and ensuring strategic biosecurity (area management with synchronized fallowing). Reuse of CF for a second salmon production cycle may reduce costs and even probability of infection (especially from wild-caught CF), but should only be considered as part of a rigorous area management programme because the practice presents opportunities for pathogens to adapt to salmon by weakening fallowing. [ABSTRACT FROM AUTHOR]

Since the mid-1980s, clinical inspections of aquaculture sites carried out on a regular basis by authorized veterinarians and fish health biologists (known as fish health services: FHS) have been an essential part of aquatic animal health surveillance in Norway. The aims of the present study were (1) to evaluate the performance of FHS routine clinical inspections for the detection of VHS and (2) to explore the effectiveness of risk-based prioritisation of FHS inspections for demonstrating freedom from VHS in marine salmonid sites in Norway. A stochastic simulation model was developed to estimate site sensitivity (SeS), population sensitivity (SeP), and probability of freedom (PFree). The estimation of SeS takes into consideration the probability that FHS submit samples if a site is infected, the probability that a sample is tested if submitted, the effective probability of infection in fish with clinical signs, laboratory test sensitivity, and the number of tested samples. SeP and PFree were estimated on a monthly basis over a 12 month period for six alternative surveillance scenarios and included the risk factors: region, species, area production density, and biosecurity level. Model results indicate that the current surveillance system, based on routine inspections by the FHS has a high capability for detecting VHS and that there is a high probability of freedom from VHS in Norwegian marine farmed salmonids (PFree >95%). Sensitivity analysis identified the probabilities that samples are submitted and submitted samples are tested, as the most influential input variables. The model provides a supporting tool for evaluation of potential changes in the surveillance strategy, and can be viewed as a platform for similar exotic viral infectious diseases in marine salmonid farming in Norway, if they share similar risk factors. [ABSTRACT FROM AUTHOR]

The importance and volume of aquaculture is increasing world-wide. Rearing practices play a key role in determining growth rate, survival and disease resistance in aquaculture fishes. Recent evidence suggests that in comparison with a standard stimulus-poor rearing environment, an enriched or variable rearing environment has significant positive effects on several traits underlying growth and well-being of fish. However, the effect of enriched rearing on one of the most important threats for aquaculture development, occurrence of parasitic infections, remains unknown., We used surveillance data of experimental salmonid populations of wild and hatchery origin under semi-natural parasite exposure to explore effects of enriched rearing on outbreaks of important aquaculture pathogens and associated fish mortalities in production-scale fish densities. We also conducted controlled parasite exposures to investigate if enriched rearing reduces susceptibility of fish to infection in comparison with standard rearing conditions., We found evidence of enriched rearing influencing survival and disease resistance of aquaculture fish during parasite epidemics. Essentially, populations from enriched rearing had a higher survival rate, lower parasite occurrence and greater resistance to most infections compared to fish held in standard rearing conditions. Similarly, fish of wild genetic background had lower mortality during some of the epidemics compared to fish of hatchery origin. However, we also demonstrate significant variation in these patterns and in some cases a tendency for opposite effects of enriched rearing and genetic background depending on the fish species and nature of the epidemic., Synthesis and applications. Our results suggest that parasitic infections and epidemics can be managed through enriched rearing conditions. This may have important implications for economically and ecologically sustainable parasite and disease prevention strategies in aquaculture. [ABSTRACT FROM AUTHOR]

Pancreas disease (PD), caused by salmonid alphavirus subtype 3 (SAV3), emerged in Norwegian aquaculture in the 1980s and is now endemic along the south-western coast. In 2011, the first cases of PD caused by marine salmonid alphavirus subtype 2 (SAV2) were reported. This subtype has spread rapidly among the fish farms outside the PD-endemic zone and is responsible for disease outbreaks at an increasing numbers of sites. To describe the geographical distribution of salmonid alphavirus (SAV), and to assess the time and site of introduction of marine SAV2 to Norway, an extensive genetic characterization including more than 200 SAV-positive samples from 157 Norwegian marine production sites collected from May 2007 to December 2012 was executed. The first samples positive for marine SAV2 originated from Romsdal, in June 2010. Sequence analysis of the E2 gene revealed that all marine SAV2 included in this study were nearly identical, suggesting a single introduction into Norwegian aquaculture. Further, this study provides evidence of a separate geographical distribution of two subtypes in Norway. SAV3 is present in south-western Norway, and marine SAV2 circulates in north-western and Mid-Norway, a geographical area which since 2010 constitutes the endemic zone for marine SAV2. [ABSTRACT FROM AUTHOR]

Salmonid alphavirus (SAV) is an enveloped, single-stranded, positive sense RNA virus belonging to the family Togaviridae. It causes economically devastating disease in cultured salmonids. The characteristic features of SAV infection include severe histopathological changes in the heart, pancreas and skeletal muscles of diseased fish. Although the presence of virus has been reported in a wider range of tissues, the mechanisms responsible for viral tissue tropism and for lesion development during the disease are not clearly described or understood. Previously, we have described membrane-dependent morphogenesis of SAV and associated apoptosis-mediated cell death in vitro. The aims of the present study were to explore ultrastructural changes associated with SAV infection in vivo. Cytolytic changes were observed in heart, but not in gill and head-kidney of virus-infected fish, although they still exhibited signs of SAV morphogenesis. Ultrastructural changes associated with virus replication were also noted in leukocytes in the head kidney of virus-infected fish. These results further describe the presence of degenerative lesions in the heart as expected, but not in the gills and in the kidney. [ABSTRACT FROM AUTHOR]

We assessed infection prevalence and intensity by the ectoparasitic copepodSalmincola californiensisamong salmonid species rearing in reservoirs and streams upstream of reservoirs in the Willamette River basin, Oregon, during 2012 and 2013. Infection levels of juvenile Chinook SalmonOncorhynchus tshawytscha, Rainbow TroutO. mykiss, and Cutthroat TroutO. clarkiiwere greater in reservoirs than in streams and increased with the age and size of fish. Copepods were more likely to be attached within the brachial cavity of reservoir fish (79%), whereas fins were the most common attachment site on stream fish (71%). Chinook Salmon in reservoirs were more vulnerable to infection than other species. Age-0 Chinook Salmon in reservoirs showed increasing infection prevalence throughout the year, reaching 84% by fall (compared with 11% in streams). Infection intensity was greater for age-0 Chinook Salmon in reservoirs than for those in streams. Infection prevalence for reservoir-rearing Rainbow Trout was < 1% at age 0, 22% at age 1, 36% at age 2, and 38% at age 3. Intensity was low for age-1 Rainbow Trout and increased for age-2 and age-3 fish. Infection prevalence for reservoir-rearing Cutthroat Trout collected in spring (39%) was greater than for those rearing in streams (4.5%). Juvenile kokaneeO. nerkawere only present in reservoirs and were rarely infected with copepods. The lack of water current in reservoirs may increase the likelihood of infection in the brachial cavity. Greater infection levels observed for juvenile Chinook Salmon compared with the other species in reservoirs may be a function of behavioral, physiological, and habitat differences. We concluded that copepod infection in reservoirs reached levels that could decrease the fitness and survival of Chinook Salmon smolts, potentially hampering conservation and recovery efforts. Received December 23, 2014; accepted May 10, 2015 [ABSTRACT FROM PUBLISHER]

Piscine reovirus (PRV) was common among wild and farmed salmonids in British Columbia, western Canada, from 1987 to 2013. Salmonid tissues tested for PRV by real-time rRT-PCR included sections from archived paraffin blocks from 1974 to 2008 ( n = 363) and fresh-frozen hearts from 2013 ( n = 916). The earliest PRV-positive sample was from a wild-source steelhead trout, Oncorhynchus mykiss (Walbaum), from 1977. By histopathology ( n = 404), no fish had lesions diagnostic for heart and skeletal muscle inflammation (HSMI). In some groups, lymphohistiocytic endocarditis affected a greater proportion of fish with PRV than fish without PRV, but the range of Ct values among affected fish was within the range of Ct values among unaffected fish. Also, fish with the lowest PRV Ct values (18.4-21.7) lacked endocarditis or any other consistent lesion. From 1987 to 1994, the proportion of PRV positives was not significantly different between farmed Atlantic salmon, Salmo salar L. (44% of 48), and wild-source salmonids (31% of 45). In 2013, the proportion of PRV positives was not significantly different between wild coho salmon, Oncorhynchus kisutch (Walbaum), sampled from British Columbia (5.0% of 60) or the reference region, Alaska, USA (10% of 58). [ABSTRACT FROM AUTHOR]

Background: Flavobacterium psychrophilum causes serious fish diseases such RTFS and BCWD, affecting the aquaculture industry worldwide. Commercial vaccines are not available and control of the disease depends on the use of antibiotics. Reliable methods for detection and identification of different isolates of this bacterium could play an important role in the development of good management strategies. The aim of this study was to identify genetic markers for discrimination between isolates. A selection of eight VNTRs from 53 F. psychrophilum isolates from Norway, Chile, Denmark and Scotland were analyzed. The results were compared with previous work on the same pathogen using MLST for genetic differentiation. Results: The VNTR analysis gave a separation between the F. psychrophilum isolates supporting the results of previous MLST work. A higher diversity was found among the Chilean isolates compared to those from Norway, which suggests a more homogenous reservoir in Norway. Transgenerational transmission of F. psychrophilum from other countries, exporting salmon embryos to Chile, may explain the differences in diversity. The same transmission mechanisms could also explain the wide geographical distribution of identical isolates in Norway. But, this could also be a result of movement of smolts and embryos. The selected VNTRs are stable genetic markers and no variation was observed after several passages on agar plates at different temperatures. Conclusions: These VNTRs are important additions for genotyping of F. psychrophilum isolates. Future studies on VNTRs of F. psychrophilum should include isolates from more host species from a wider geographical area. To get a more robust genotyping the VNTRs should be used in concert with MLST. Future studies of isolates with high and low virulence should focus on identifying virulence markers using VTNRs and MLST. [ABSTRACT FROM AUTHOR]

Tetracapsuloides bryosalmonae (Myxozoa) is the causative agent of proliferative kidney disease in various species of salmonids which are found in Europe and North America. Less information about the interactions of T. bryosalmonae proteins with salmonid proteins during parasite development is known. In this study, anti- T. bryosalmonae monoclonal antibody-linked to N-hydroxysuccinimide-activated spin columns were used to purify parasite and host proteins from the kidneys of infected and non-infected brown trout ( Salmo trutta) Linnaeus, 1758. The samples were next analyzed by electrospray ionization coupled to mass spectrometry to identify proteins that may be involved in the infection and proliferation of T. bryosalmonae within the brown trout host. A total of 6 parasite proteins and 40 different host proteins were identified in this analysis. The identified host proteins function in various processes, which include host defense, enzymatic, and structural components. In conjunction with modern molecular based tools, such siRNA, gene replacement, or gene disruption, this data can ultimately be used to develop novel control methods for T. bryosalmonae, based on the proteins or pathways identified in this study. [ABSTRACT FROM AUTHOR]

Pancreas disease ( PD) in Norwegian salmonid aquaculture has traditionally been caused by salmonid alphavirus ( SAV) subtype 3. Following the isolation of a novel SAV subtype in 2010, marine SAV2, two separate endemic areas have developed. It has been debated whether disease outbreaks due to marine SAV2 result in milder clinical manifestations compared to outbreaks caused by SAV3. The aim of this study was to descriptively investigate site-level differences in the clinical manifestations of marine SAV2 and SAV3 at Norwegian seawater sites diagnosed with PD in 2012. The findings suggest that Norwegian PD outbreaks caused by marine SAV2 result in lower mortality and milder clinical signs compared to outbreaks caused by SAV3. For sites without reported PD-related mortality, there was no difference in the mortality levels between sites infected by marine SAV2 and SAV3. The results also indicate that there are no differences in grading quality at slaughter between the SAV subtypes. [ABSTRACT FROM AUTHOR]

Rivers originating from the areas of active volcanism in Kamchatka serve a spawning ground for anadromous and resident populations of dolly varden ( Salvelinus malma). In some cases, watercourses with a long-term continuous spawning of S. malma are subjected to chronic pollution with dissolved toxicants and suspended mineral particles. The revealed development conditions range from background ('clean' rivers) to critical (most 'polluted' rivers). Medium pollution leads to the development of hatchlings with abnormalities in the ethmoidal head segment, lower jaw, operculum, lobes of the paired fins, and axial skeleton (up to 40% of all specimens). Delayed ossification of skeletal elements takes place. Abnormalities in the development of spinous processes occur more often (up to 49-55% compared to 25-30% in the background areas). The average number of asymmetries per specimen (in four bilateral structures) increases from 1.1-1.4 to 1.7-2.5. Similar developmental abnormalities have been registered in underyearlings, both anadromous and resident, influenced by various pollutant combinations. While fish continue to grow, some of them die because of abnormalities; thus, their frequency in 3-year-old specimens nears the background one. Upon extreme pollution, deviant specimens are sampled at earlier developmental stages and characterized by a lower frequency of morphological abnormalities. [ABSTRACT FROM AUTHOR]

The article explores the role of fish immunization agent as preventive medical protection against the Flavobacterium psychrophilum which causes bacterial cold-water disease (BCWD) among ayu sweetfishes. A historical overview about the development studies to prevent the spread of BCWD among fishes and salmonid fishes is noted. It conclude the importance of specific antibody production through increasing phagocytic and bactericidal activity of serum against F. psychrophilum in ayu fishes.

Mx proteins are main effectors of the antiviral innate immune defence mediated by type I interferon (IFN I). The IFN I response is under a complex regulation; hence, one of the key issues in understanding virus-host interaction is the knowledge of the regulatory mechanisms governing this response. With this purpose, in this study Chinook salmon embryo cells (CHSE-214) and rainbow trout gonad cells (RTG-2) were transiently transfected with a vector containing the luciferase reporter gene under the control of the Senegalese sole Mx promoter. These transfected cells were infected with infectious pancreatic necrosis virus (IPNV), viral haemorrhagic septicaemia virus (VHSV) and epizootic haematopoietic necrosis virus (EHNV) at different doses in order to study the luciferase fold induction in response to viral infections. Transfected CHSE-214 cells infected with EHNV showed significant induction of the luciferase reporter gene, compared to control non-infected cells, at different times post infection (p.i.). The maximum expression was recorded at 24 h p.i. in cells inoculated with 5 × 10 2 TCID 50 /mL (2.17 folds compared to control cells). In these cells, the infection with IPNV and VHSV did not result in the luciferase expression at any time and doses tested. In transfected RTG-2 cells, VHSV stimulated luciferase expression, obtaining a maximum activity at 48 h p.i. in cells infected with 5 × 10 2 TCID 50 /mL (2.9 folds compared to control cells), whereas RTG-2 cells infected with IPNV and EHNV did not show significant luciferase activity at any time point. The different induction of the Senegalese sole Mx promoter in CHSE-214 and RTG-2 cells after infection with the same viruses indicates that cell-specific factors are significantly involved in the IFN-signalling response, and, probably, on the success of the strategies of these viruses to escape the IFN mechanisms. The use of these two different cellular systems might be an interesting approach to identify such cellular factors. [ABSTRACT FROM AUTHOR]

Piscirickettsia salmonis is the pathogen responsible for salmonid rickettsial septicemia (SRS), a disease that affects a wide variety of marine cultivated fish species and causes economic losses for the aquaculture industry worldwide. Many in vitro studies have reported on the capacity of this microorganism to replicate in the interior of cytoplasmic vesicles from varied fish cell lines. However, the mechanisms used by this bacteria to survive, replicate, and propagate in cell lines, especially in macrophages and monocytes, are unknown. A number of studies have described the diverse proteins in pathogens such as Legionella pneumophila , Coxiella burnetii , and Francisella tularensis which allow these to evade the cellular immune response and replicate in the interior of macrophages in different hosts. Some of these proteins are the virulence factor BipA/TypA and the heat shock protein ClpB, both of which have been widely characterized. The results of the current study present the complete coding sequence of the genes clp B and bip A from the P. salmonis genome. Moreover, the experimental results suggest that during the infectious process of the SHK-1 cellular line in P. salmonis , the pathogen significantly increases the expression of proteins ClpB and BipA. This would permit the pathogen to adapt to the hostile conditions produced by the macrophage and thus evade mechanisms of cellular degradation while facilitating replication in the interior of this salmon cell line. [ABSTRACT FROM AUTHOR]

Anthropogenic warming of stream temperature and the presence of exotic diseases such as whirling disease are both contemporary threats to coldwater salmonids across western North America. We examined stream temperature reduction over a 15-year prerestoration and postrestoration period and the severity ofMyxobolus cerebralisinfection (agent of whirling disease) over a 7-year prerestoration and postrestoration period in Kleinschmidt Creek, a fully reconstructed spring creek in the Blackfoot River basin of western Montana. Stream restoration increased channel length by 36% and reduced the wetted surface area by 69% by narrowing and renaturalizing the channel. Following channel restoration, average maximum daily summer stream temperatures decreased from 15.7°C to 12.5°C, average daily temperature decreased from 11.2°C to 10.0°C, and the range of daily temperatures narrowed by 3.3°C. Despite large changes in channel morphology and reductions in summer stream temperature, the prevalence and severity ofM. cerebralisinfection for hatchery Rainbow TroutOncorhynchus mykissremained high (98–100% test fish with grade > 3 infection) versus minimal for hatchery Brown TroutSalmo trutta(2% of test fish with grade-1 infection). This study shows channel renaturalization can reduce summer stream temperatures in small low-elevation, groundwater-dominated streams in the Blackfoot basin to levels more suitable to native trout. However, because of continuous high infections associated with groundwater-dominated systems,the restoration of Kleinschmidt Creek favors brown troutSalmo truttagiven their innate resistance to the parasite and the higher relative susceptibility of other salmonids. Received February 3, 2014; accepted May 3, 2014 [ABSTRACT FROM AUTHOR]

Highlights: [•] The type I Interferon is induced in salmonids following infection with all known types of viruses. [•] Dendritic cells and natural killer cell markers have been identified in salmonids and their involvement in viral infection confirmed. [•] Viruses have evolved immune evasion mechanisms. [Copyright &y& Elsevier]

Renibacterium salmoninarum is the causative agent of bacterial kidney disease, a major pathogen of salmonid fish species worldwide. Very low levels of intra-species genetic diversity have hampered efforts to understand the transmission dynamics and recent evolutionary history of this Gram-positive bacterium. We exploited recent advances in the next-generation sequencing technology to generate genome-wide single-nucleotide polymorphism (SNP) data from 68 diverse R. salmoninarum isolates representing broad geographical and temporal ranges and different host species. Phylogenetic analysis robustly delineated two lineages (lineage 1 and lineage 2); futhermore, dating analysis estimated that the time to the most recent ancestor of all the isolates is 1239 years ago (95% credible interval (CI) 444-2720 years ago). Our data reveal the intercontinental spread of lineage 1 over the last century, concurrent with anthropogenic movement of live fish, feed and ova for aquaculture purposes and stocking of recreational fisheries, whilst lineage 2 appears to have been endemic in wild Eastern Atlantic salmonid stocks before commercial activity. The high resolution of the SNP-based analyses allowed us to separate closely related isolates linked to neighboring fish farms, indicating that they formed part of single outbreaks. We were able to demonstrate that the main lineage 1 subgroup of R. salmoninarum isolated from Norway and the UK likely represent an introduction to these areas ∼40 years ago. This study demonstrates the promise of this technology for analysis of micro and medium scale evolutionary relationships in veterinary and environmental microorganisms, as well as human pathogens. [ABSTRACT FROM AUTHOR]

Whirling disease, caused by the myxozoan parasite Myxobolus cerebralis, is a serious health threat to salmonid fish and its control remains problematic. The parasite has a 2-host life cycle involving a salmonid and the aquatic oligochaete Tubifex tubifex. A commonly used strategy to control parasites that requires an obligatory invertebrate host is to eliminate or reduce the host population size to a point where parasite transmission can no longer occur. Large numbers of T. tubifex are frequently found in degraded habitats that are characterized by an abundance of fine sediments, organic matter, and a lack of aquatic invertebrate diversity. If such environments are rehabilitated, then the normal flora and fauna should re-establish and the numbers of T. tubifex should decline due to their inability to compete with the re-established invertebrates. During an epizootiological study on Rock Creek, located in west-central Montana, 2 opportunities were available to examine the effects of habitat restoration on the transmission of M. cerebralis. The Puyear Ranch re-establishment project was a major endeavor conducted on the main channel of Rock Creek, a little more than midway upstream. Another significant restoration was conducted on Upper Willow Creek, a tributary of Rock Creek, located closer to the headwaters. Sentinel trout studies, along with examining T. tubifex for the parasite and measuring various water-quality parameters, revealed that the restoration of the Puyear Ranch locality had no significant effect on reducing the intensity of M. cerebralis in trout. This was likely due to the restored area being located mid-river, just downstream from a 'hot spot' of infected T. tubifex. In comparison, there was a significant reduction in the intensity of M. cerebralis in sentinel fish after the Upper Willow Creek restoration project was completed. Unlike the Puyear Ranch locality, there was no hot spot of infected T. tubifex above the area rehabilitated on Upper Willow Creek. Further, the relative abundance of T. tubifex and M. cerebralis-infected worms was reduced. Although further study is needed, it appears that habitat rehabilitation can reduce the transmission of M. cerebralis. Since the triactinomyxon stage of the parasite released from T. tubifex (which infects trout) can float for many kilometers, the rehabilitation of a hot spot may reduce the infection of trout downstream where they inhabit a healthy environment with no M. cerebralis-infected T. tubifex in the vicinity. Thus, rehabilitation of a relatively small area could significantly affect the drainage for many kilometers beyond the improved habitat. [ABSTRACT FROM AUTHOR]

Abstract: An attenuated strain of Flavobacterium psychrophilum (CSF259-93B.17) has shown potential as a vaccine for prevention of bacterial coldwater disease (BCWD) in rainbow trout, Oncorhynchus mykiss (Walbaum). Because BCWD outbreaks can result in high mortality in other salmonid species, specifically coho salmon, Oncorhynchus kisutch (Walbaum), the live-attenuated strain was tested as a vaccine in this species. Additionally, we hypothesized that culture of the vaccine strain under iron-limited conditions would lead to improved protection against BCWD. To test this hypothesis, coho salmon were either injection or immersion immunized with CSF259-93B.17 cultured in iron-replete or iron-limited medium. Resultant antibody titers were low and not significantly different between the two treatments regardless of vaccine delivery method (P > 0.05). Following injection challenge with a virulent F. psychrophilum strain, mortality for injection vaccinated fish was significantly reduced compared to the control but did not differ by treatment (P > 0.05). Relative percent survival (RPS) was high in both treatments (90% in iron-replete, 98% in iron-limited medium). Fish immunized by immersion with CSF259-93B.17 grown in iron-replete medium exhibited lower mortality (29.3%; RPS 46%) when compared to mock immunized fish, but this was not significant. However, mortality was significantly lower in fish immunized with CSF259-93B.17 grown in iron-limited medium (14.7%; RPS 73%) when compared to mock immunized fish. The results demonstrate that the live-attenuated F. psychrophilum strain can confer protection to coho salmon and vaccine efficacy is enhanced by culturing the strain under iron-limited conditions. [Copyright &y& Elsevier]

No gold standard assay exhibiting error-free classification of results has been identified for detection of Renibacterium salmoninarum, the causative agent of salmonid bacterial kidney disease. Validation of diagnostic assays for R. salmoninarum has been hindered by its unique characteristics and biology, and difficulties in locating suitable populations of reference test animals. Infection status of fish in test populations is often unknown, and it is commonly assumed that the assay yielding the most positive results has the highest diagnostic accuracy, without consideration of misclassification of results. In this research, quantification of R. salmoninarum in samples by bacteriological culture provided a standardized measure of viable bacteria to evaluate analytical performance characteristics (sensitivity, specificity and repeatability) of non-culture assays in three matrices (phosphate-buffered saline, ovarian fluid and kidney tissue). Non-culture assays included polyclonal enzyme-linked immunosorbent assay ( ELISA), direct smear fluorescent antibody technique ( FAT), membrane-filtration FAT, nested polymerase chain reaction (nested PCR) and three real-time quantitative PCR assays. Injection challenge of specific pathogen-free Chinook salmon, Oncorhynchus tshawytscha ( Walbaum), with R. salmoninarum was used to estimate diagnostic sensitivity and specificity. Results did not identify a single assay demonstrating the highest analytical and diagnostic performance characteristics, but revealed strengths and weaknesses of each test. [ABSTRACT FROM AUTHOR]

Studies on the ultrastructural morphogenesis of viruses give an insight into how the host cell mechanisms are utilized for new virion synthesis. A time course examining salmonid alphavirus 1 ( SAV 1) assembly was performed by culturing the virus on Chinook salmon embryo cells ( CHSE-214). Different stages of viral replication were observed under electron microscopy. Virus-like particles were observed inside membrane-bound vesicles as early as 1 h following contact of the virus with the cells. Membrane-dependent replication complexes were observed in the cytoplasm of the cells, with spherules found at the periphery of late endosome-like vacuoles. The use of intracellular membranes for RNA replication is similar to other positive-sense single-stranded RNA (+ss RNA) viruses. The number of Golgi apparatus and associated vacuoles characterized by 'fuzzy'-coated membranes was greater in virus-infected cells. The mature enveloped virions started to bud out from the cells at approximately 24 h post-infection. These observations suggest that the pathway used by SAV 1 for the generation of new virus particles in vitro is comparable to viral replication observed with mammalian alphaviruses but with some interesting differences. [ABSTRACT FROM AUTHOR]

Abstract: Salmon pancreas disease, caused by salmonid alphavirus (SAV) of the family Togaviridae, is an economically important disease affecting farmed Atlantic salmon (Salmo salar L.) in Scotland, Norway, and Ireland. The virus causes characteristic lesions in the pancreas, heart, kidney and skeletal muscle of infected fish. The mechanisms responsible for the pathology and the immune responses elicited in infected Atlantic salmon are not fully understood. A microarray-based study was therefore performed to evaluate the host transcriptomic response during the early stages of an experimentally-induced SAV-1 infection. Atlantic salmon parr were injected intra-peritoneally with viral cell culture supernatant or cell culture supernatant without virus. RNA, extracted from head kidney sampled from infected and control fish at 1, 3 and 5 days post-injection (d.p.i.), was interrogated with the 17 k TRAITS/SGP cDNA microarray. The greatest number of significantly differentially expressed genes was recorded at 3 d.p.i., mainly associated with immune and defence mechanisms, including genes involved in interferon I pathways and Major Histocompatibility Complex Class I and II responses. Genes associated with apoptosis and cellular stress were also found to be differentially expressed between infected and uninfected individuals, as were genes involved in inhibiting viral attachment and replication. The microarray results were validated by follow-on analysis of eight genes by real-time PCR. The findings of the study reflect mechanisms used by the host to protect itself during the early stages of SAV-1 infection. In particular, there was evidence of rapid induction of interferon-mediated responses similar to those seen during mammalian alphavirus infections, and also early involvement of an adaptive immune response. This study provides essential knowledge to assist in the development of effective control and management strategies for SAV-1 infection. [Copyright &y& Elsevier]

This article describes the assumptions and calculations underlying best estimates of the direct and indirect costs of three salmonid diseases in the United Kingdom: infectious salmon anaemia (ISA), viral haemorrhagic septicaemia (VHS), and infectious haemorrhagic necrosis (IHN) using a standardized spreadsheet-based model. The data input for the model was derived from the literature and from a small survey specifically conducted to obtain the additional information required. The costs of private and public surveillance, treatment, prevention, and eradication of the known outbreaks of ISA and VHS, and a simulated outbreak of IHN, were estimated. The average current costs of all aquaculture disease surveillance and control by the private and public sectors averaged £17.6 million per annum, of which the private sector share of expenditure averaged 80% per annum. Specific disease surveillance and control costs for three diseases ranged between £4.7 million and £5.6 million per annum. While the current literature supports the concept that indirect costs (such as export trade restriction and consumer response to disease outbreak) have the capacity to cause major losses in the industry, the indication in our model is that the magnitude of indirect costs for salmonid disease outbreak is not significant. [ABSTRACT FROM AUTHOR]

The article presents a study on the outbreaks of spironucleosis in farmed Atlantic salmon, Salmo salar, in northern Norway. It says that the outbreaks were from smolts that came from the same farm after it was found that an outbreak of systemic spirnucleosis in farmed Arctic char showed that the parasite from the gall bladder of wild Arctic char was genetically different from those causing systemic disease in farmed fish through electron microscopy. It explains that through molecular methods, Spironucleus salmonicida, a diplomonad flagellate that causes systemic infections in farmed salmonids, are also present in wild salmonids who serve as reservoir hosts of the diplomonad flagellate.

Abstract: Mx proteins are crucial effectors of the innate antiviral response mediated by the interferon type I signalling pathway. Recently, three Mx proteins, named SauMx1, SauMx2 and SauMx3, corresponding to three different genes, have been identified in the cultured marine species gilthead seabream (Sparus aurata). In this study, the three SauMx cDNAs were cloned into expression vectors and used for transfection of CHSE-214 cells. Monoclonal cell populations stably expressing each recombinant protein have been obtained and characterized. The protection conferred by each recombinant SauMx against Infectious Pancreatic Necrosis Virus (IPNV) infection has been in vitro evaluated, having found clear differences among them. According to the cytopathic effects and the virus yield reduction assays, only cells expressing SauMx2 and SauMx3 showed significant resistance to IPNV infection. Otherwise, quantitative RT real-time PCR assays suggested that each SauMx protein has a different target during the viral inhibition process. The differences observed among the three SauMx proteins are discussed in terms of their differential mechanism of action and antiviral specificity, suggesting, as a whole, to play a synergistic activity in the protection of gilthead seabream against IPNV. [Copyright &y& Elsevier]

A comparative challenge study of six marine isolates representing subtypes 1-6 of salmonid alphavirus ( salmon pancreas disease virus, Genus Alphavirus, Family Togaviridae) was conducted in Atlantic salmon in a fresh water cohabitation trial. Histopathological lesions typical of pancreas disease were observed with all subtypes, and virus was re-isolated from serum of cohabitant fish in each case. Using a virus neutralization (VN) test neutralizing salmonid alphavirus (SAV) subtype 1 strain F93-125, VN antibodies were detected in all challenge groups, consistent with serological cross-reactivity between these subtypes. Using real-time RT-PCR, SAV RNA was detected in heart tissue from 2 to 3 weeks post-challenge (wpc) in all cohabitant groups excluding controls. The results obtained suggested differences in the dynamics of infection between strains of SAV and potentially between subtypes. Results for SAV subtypes 1 and 3 suggested essentially synchronous infection of cohabitant fish. These two study groups also had the highest virus load in heart tissue as measured by quantitative RT-PCR and also had the most extensive histopathological changes. In contrast, results for SAV subtypes 2 and 6 strains were consistent with asynchronous infection in the cohabitant fish and were characterized by slow spread, low virus loads and mild histopathological changes. The SAV subtype 4 and 5 strains occupied an intermediate position in this regard. Despite the use of concentration procedures, it was not possible to detect SAV RNA in water samples from selected study tanks. However, testing of faeces from the SAV subtypes 1, 3 and 6 challenge groups found positive signals in each beginning at 1-3 wpc and remaining detectable for a further 2-3 weeks. Parallel testing of mucus samples found these became positive at 2-3 wpc and remained positive for a further 1-3 weeks. These results demonstrate for the first time that shedding and transmission of virus may occur by both these routes and suggest that dispersal in these matrices should be included in any disease transmission models. [ABSTRACT FROM AUTHOR]

A three-gene operon, named yctCBA (Yersinia citrate transporter), induced by citrate and repressed by glucose was identified from a previously selected in vivo-induced (ivi) clone in the fish pathogen Yersinia ruckeri. Interestingly, despite being an ivi clone, the drastic growth reduction of the yctC mutant in the presence of citrate, and the relatively high content of this compound in rainbow trout serum, the operon was not required for virulence. [ABSTRACT FROM AUTHOR]

Abstract: We conducted a dietary feeding study with juvenile chinook salmon (Oncorhynchus tshawytscha) to assess the potential for tributyltin (TBT) to elicit the obesogen response that has been described for mammals. The results show increases in whole-body lipid content, which is consistent with the obesogen response; however, we also observed associated parameters that were dissimilar. We found increases in body mass and alterations to several physiological parameters at doses between 0.4 and 3.5ng/g fish/day (1.4–12pmol/g fish/day) and reduced body mass at the highest dose after 55 days of exposure. Lipid related plasma parameters (plasma triacylglycerols, cholesterol, and lipase) exhibited monotonic increases over all doses while other values (glucose and insulin-like growth factor (IGF)) exhibited increases only for the low-dose treatments. The increases noted for several parameters in fish were opposite to those reported for the obesogen metabolic syndrome, which is characterized by a reduction in serum glucose, free fatty acids, and triglycerides. This is the first report of growth stimulation resulting from low-dose exposure to this pesticide, which is an unusual response for any animal exposed to an organic or organometallic xenobiotic. Because a number of environmental contaminants act as metabolic disruptors at very low doses, these results are noteworthy for a variety of species. Intuitively, enhanced growth and lipid storage may appear beneficial; however, for salmonids there are numerous potentially negative consequences for populations. [ABSTRACT FROM AUTHOR]

The article investigates the potential reservoir of salmonid alphaviruses in wild marine fish species and the implications for the origins of salmon pancreas disease in aquaculture. Salmonid alphavirus carries the etiological agents of salmon pancreas disease in farmed Atlantic salmon and sleeping disease in rainbow trout. The verification of the specificity of sensitive real-time PCR detections is explained. The molecular epidemiological analysis of tissue samples from fish species is discussed.