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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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

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.

The article presents a study which examined the presence of Renibacterium salmoninarum as a causative agent of bacterial kidney disease in salmonids by using the enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction assay (qPCR). It states that the conceptual model that allows inferences may have utility in broodstock selection programs which use egg-culling practices solely based on ELISA. The authors opted to conduct dual analysis on a single amount of tissue as the samples are limited.

Background: Pancreas disease (PD) is a viral fish disease which in recent years has significantly affected Norwegian salmonid aquaculture. In Norway, the aetiological agent salmonid alphavirus (SAV) has been found to be represented by the subtype 3 only. SAV subtype 3 has in previous analyses been found to show a lower genetic divergence than the subtypes found to cause PD in Ireland and Scotland. The aim of this study was to evaluate the nucleotide (nt) and amino acid divergence and the phylogenetic relationship of 33 recent SAV subtype 3 sequences. The samples from which the sequences were obtained originated from both PD endemic and nonendemic regions in an attempt to investigate agent origin/spread. Multiple samples throughout the seawater production phase from several salmonid populations were included to investigate genetic variation during an outbreak. The analyses were mainly based on partial sequences from the E2 gene. For some samples, additional partial 6 K and nsP3 gene sequences were available. Results: The nucleotide divergence for all gene fragments ranged from total identity (0.0% divergence) to 0.45% (1103 nt fragment of E2), 1.11% (451 nt fragment of E2), 0.94% (6 K) and 0.28% (nsP3). This low nucleotide divergence corresponded well to previous reports on SAV 3 sequences; however the observed divergence for the short E2 fragment was higher than that previously reported. When compared to SAVH20/03 (AY604235), amino acid substitutions were detected in all assessed gene fragments however the in vivo significance of these on for example disease outbreak mortality could not be concluded on. The phylogenetic tree based on the 451 nt E2 fragment showed that the sequences divided into two clusters with low genetic divergence, representing only a single SAV subtype. Conclusions: The analysed sequences represented two clusters of a single SAV subtype; however some of the observed sequence divergence was higher than that previously reported by other researchers. Larger scale, full length sequence analyses should be instigated to allow further phylogenetic and molecular epidemiology investigations of SAV subtype 3. [ABSTRACT FROM AUTHOR]

The life cycle from release of myxospore sporoplasm to mature actinospore for the myxozoan parasite Ceratomyxa shasta in the freshwater polychaete host is described. Infection was initiated through exposure to lab-infected waters. Mature myxospores were present in the gut of segment 4 by 2 hr post-exposure (PE). Migration of early developmental stages occurred from the gut epithelium, through the nervous system, and into the epidermis. Once the parasite reached the epidermis, development typically occurred in segments 6-10. Life stages in the epidermis included a proliferative stage (schizogony), development of a pansporocyst (gametogony), sexual reproduction (gametogamy), and spore formation (sporogony). At water temperatures averaging 17.3 C, schizogony began by 3 hr PE, gametogony by 14 days PE, gametogamy by 35 days PE, and sporogony between 35 and 49 days PE. Development of mature actinospores took approximately 49 days PE. Up to 13,650 ± 7,807 actinospores could be released from a single polychaete over a 14-day period. Actinospores appeared to be released directly through the epidermis into the water column. [ABSTRACT FROM AUTHOR]

Myxobolus cerebralis, the causative agent of whirling disease, infects both salmonid fish and an aquatic oligochaete, Tubifex tubifex. Although M. cerebralis has been detected in river drainages throughout the United States, disease severity among wild fish populations has been highly variable. Tubifex tubifex populations have been genetically characterized using sequences from the 16S mitochondrial DNA (mtDNA) gene, the 18S ribosomal RNA gene, the internal transcribed spacer region 1 (ITS1), and randomly amplified polymorphic DNA (RAPD). Our earlier work indicated that large differences in compatibility between the parasite and populations of T. tubifex may play a substantial role in the distribution of whirling disease and resulting mortality in different watersheds. In the present study, we examined 4 laboratory populations of T. tubifex belonging to 16S mtDNA lineage III and 1 population belonging to 16S mtDNA lineage I for triactinomyxon (TAM) production after infection with M. cerebralis myxospores. All 4 16S mtDNA lineage III populations produced TAMs, but statistically significant differences in TAM production were observed. Most individuals in the 16S mtDNA lineage III-infected populations produced TAMs. The 16S mtDNA lineage I population produced few TAMs. Further genetic characterization of the 16S mtDNA lineage III populations with RAPD markers indicated that populations producing similar levels of TAMs had more genetic similarity. [ABSTRACT FROM AUTHOR]

Habitat assessments were conducted in an intermountain watershed at three spatial extents to explore ways to predict the presence of tubificid oligochaetes likely to support the parasite Myxobolus cerebralis, cause of salmonid whirling disease. Stream reaches with six different reach slope characteristics were selected using GIS. The aquatic habitat in 60 reaches selected at random was measured and classified into distinct habitat units. Within the habitat units, areas of microhabitat with depositional fine sediments were chosen, measured, and core samples were removed to characterize the sediments and benthic oligochaetes. Two tubificids, Tubifex spp. and Limnodrilus hoffmeisteri, were abundant and co-occurred in silt-clay and fine sand sediments in these habitats. Models were posed and tested to predict the presence and relative abundance of tubificids using habitat characteristics from the three spatial extents: reach, habitat unit, and microhabitat. At the reach extent, tubificids were associated with low-reach slope and with slow water habitats. Within habitat units, tubificids were associated with higher percentages of fine sediments and higher stream width:depth ratios. In microhabitat cores, the presence of silt-clay sediments was positively associated with higher average stream width:depth ratios. Since ecological relationships are often scale dependent and stream systems have a natural hierarchy, predictive habitat models such as these that use measures from several scales may help researchers and managers more efficiently identify and quantify aquatic communities at highest risk of infection by the M. cerebralis parasite. [ABSTRACT FROM AUTHOR]

The article presents a study that investigates the epizootiology of Myxobolus cerebralis concerning the salmonid whirling disease in the Rock Creek watershed of west-central Montana. The study aims to elucidate the myriad parameters involved in the transmission dynamics of whirling disease throughout an important trout habitat. It was observed that the parasite has caused a decline in rainbow trout densities but increased in brown trout population.

Discusses whirling disease of salmonid fishes. Life cycle of myxobolus cerebralis; Interaction between myxobolus cerebralis and its salmonid hosts; Ability of the cerebralis to infect a wide variety of salmonid hosts.

Examines the characterization of renibacterium salmoninarum extracellular products. Definition of renibacterium salmoninarum; Materials and methods used in this study; Details on the results of the study.

Background: The myxozoan Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), is responsible for considerable losses in farmed and wild fish populations in Europe and North America. Recently, T. bryosalmonae was detected in many European countries, and strategy to control the disease in the wild and farmed fish population is yet to be developed. Recombinase polymerase amplification (RPA) is a novel isothermal nucleic acid amplification technology that does not require any thermal cycling, and lateral flow dipstick (LFD) is a rapid, cost-effective, and easy-to-handle assay that enables stable detection. Results: In this study, we developed and optimized a rapid and sensitive RPA assay combined with an LFD for the detection of T. bryosalmonae. The PKD-RPA assay was specific to T. bryosalmonae, as no cross-reaction or false positive signals were observed with any of the other tested DNAs. The developed PKD-RPA assay was ten times more sensitive than an existing diagnostic polymerase chain reaction (PCR) assay for this parasite. The estimated time to perform PKD-RPA assay is 25 min compared to 4 h for PKD-PCR assay. Conclusions: A novel PKD-RPA assay for the detection of T. bryosalmonae was developed. The assay offers considerable advantages including speed, sensitivity, specificity and visual detection. Applying the PKD-RPA assay combined with an LFD enhances the surveillance and early detection of T. bryosalmonae in salmonids. [ABSTRACT FROM AUTHOR]

Piscirickettsia salmonis , the causative agent of salmonid rickettsial septicemia (SRS), is a significant threat to the healthy and sustainable production of salmonid farming industry. This Gram-negative bacterium, originally isolated from a coho salmon in Southern Chile, produces a systemic infection characterized by colonization of several fish organs. P. salmonis is able to infect, survive, and replicate inside salmonid macrophages however little is known about its mechanisms of pathogenesis. Here, we present the whole genome sequence and annotation of the P. salmonis reference strain LF-89 (ATCC VR-1361). The genome contains one circular chromosome of 3,184,851 bp and three plasmids, pPSLF89-1 (180,124 bp), pPSLF89-2 (33,516 bp) and pPSLF89-3 (51,573 bp). A total of 2850 protein-coding genes, 56 tRNAs and six copies of 5S–16S–23S rRNA. [ABSTRACT FROM AUTHOR]

Focuses on an outbreak of infectious salmon anemia at a Maine salmon farm in June 2003. Depopulation of affected fish farms; Control measures instituted in neighboring salmon farms.