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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]

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]

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.

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 initial site of infection in the fish host for Tetracapsula bryosalmonae , causative agent of proliferative kidney disease (PKD) is poorly understood. Following the recent recognition that freshwater bryozoans harbour the infective stages to salmonid fish, experimental transmission studies were undertaken to investigate (1) the route of entry of the parasite into the fish host and (2) the minimum exposure time required to induce clinical signs of PKD. In-situ hybridization (ISH) studies were carried out on naïve rainbow trout exposed to the naturally infected bryozoan Fredericella sultana for up to 90 min. The sporoplasm of T. bryosalmonae was detected entering the fish via mucous cells in the skin epithelium within the first minute of exposure. In addition, T. bryosalmonae cells were infrequently detected in the skeletal musculature of exposed experimental fish up to 72 h post-exposure. The route of migration through the fish to the kidney and spleen was not determined. All fish exposed to infected, disrupted bryozoans for 10, 30 and 90 min and maintained for up to 8 weeks developed clinical PKD. [ABSTRACT FROM AUTHOR]

Freshwater bryozoans have recently been identified as hosts of Tetracapsula bryosalmonae , the causative agent of proliferative kidney disease (PKD). To gain insight as to which bryozoans are consistently important hosts for T. bryosalmonae , we present the results of a broad scale survey of bryozoans in European and North American sites upstream from PKD outbreaks in feral, stocked and farmed salmonids. The bryozoan genera most commonly found in association with disease outbreaks are Fredericella and Plumatella , and the most common species are F. sultana (Blumenbach), F. indica Annandale, and P. emarginata Allman. The prevalence of mature sac stages of T. bryosalmonae was very low. Our survey data together with knowledge of bryozoan life cycles and the ecology of PKD allow inferences concerning unknown aspects of the life cycle of T. bryosalmonae . [ABSTRACT FROM AUTHOR]

Proliferative kidney disease (PKD) is caused by the infection of susceptible salmonid fish with spores of the myxozoan Tetracapsula bryosalmonae, a parasite harboured and released by several species of bryozoans. Under natural conditions, PKD is a water-borne infection of fish, whose outcome and spatio-temporal dissemination depend on the viability of spores present in the water. In order to evaluate the duration of parasite infectivity, juvenile rainbow trout, Oncorhynchus mykiss, were exposed for 20 h to T. bryosalmonae-infected water at various times post-water collection or after different filtration procedures. When infected water was held in a temperature range of 14.517 °C for up to 14 days, PKD was transmitted to the fish only between 0 and 12 h post-water collection and its infectivity vanished between 12 and 24 h. Similarly, the infectivity of water passed through 25 µm but not through 1 µm mesh filters, and was lost in the material eluted from the 1 µm filtration membrane although the parasite's DNA was amplified from this material. The parasitic infectivity in water appears to be fragile and this may offer opportunities to decrease the impact of PKD in trout farms by the implementation of management procedures aimed at reducing the number of the bryozoan-holding surfaces located in the river, immediately upstream from these farms. [ABSTRACT FROM AUTHOR]

Out of 19 Vibrio harveyi isolates obtained from a diversity of hosts and geographical locations, 14 were pathogenic to rainbow trout, Oncorhynchus mykiss (Walbaum), and Atlantic salmon, Salmo salar L., with mortalities of up to 100% following intraperitoneal injections of 106 cells fish-1. The extracellular products (ECPs) of only five pathogenic isolates were harmful to fish. Both pathogenic and non-pathogenic cultures produced ECPs containing caseinase, gelatinase, phospholipase, lipase and haemolysins. Vibrio harveyi VIB 645, which was the most pathogenic isolate, produced ECPs with a maximal effect on salmonids from preparations obtained by using cellophane overlays on tryptone soya agar supplemented with 1% (w/v) sodium chloride with incubation at 28 °C for 24 h. This preparation contained the highest titre of haemolytic activity to Atlantic salmon (1:256) and rainbow trout (1:32) erythrocytes. [ABSTRACT FROM AUTHOR]

Focuses on the application of polymerase chain reaction primers for detection of proliferative kidney disease organism (PKX), the causative agent of proliferative kidney disease (PKD) of salmonids. Identification of PKD as a serious parasitic disease of salmonids that causes severe losses to the rainbow trout; Clinical and pathological aspects of the condition and ultrastructural features of the PKX; Extraction of genomic DNA from PKX-infected kidney.

Experimental infections with Piscirickettsia salmonis via incraperitoneal (IP), oral (PO) and gill (GS) routes were compared, and the importance of physical contact in the horizontal transmission of this organism was investigated. Atlantic salmon, Salmo salar L., under-yearling parr raised in fresh water were used in this study. Samples of liver, kidney, spleen, gill and brain were collected weekly for 5 weeks after challenge, and were examined using the indirect fluorescent-antibody technique (IFAT). The pathogen was transmitted horizontally to fish with and without physical contact. However, transmission of P. salmonis occurred significantly more rapidly among fish with physical contact. Mortalities occurred in 50% of fish experimentally challenged with P. salmonis and their cohabitants. The estimates of the relative risk of dying demonstrated that fish challenged by the IP and GS routes had a significantly higher probability of dying than fish challenged by the PO route (P< 0.005). Contact cohabitants with infected fish had a higher probability of death than non-contact cohabitants (P< 0.005). The sequential studying using IFAT indicated that a haematogenous pattern of infection occurred among fish infected by oral and gill routes, or by cohabitation. This was different from the capsular (serosal) infection pattern observed in intraperitoneally inoculated fish. Piscirickettsia salmonis was observed within the cytoplasm of leucocytes and renal tubules, the latter indicating that elimination of this pathogen through the urine may be possible. Aeromonas salmonicida was also detected (by IFAT) in some of the fish exposed to P. salmonis, suggesting that P. salmonis may cause immunosuppression, and thus, increase the susceptibility of the host to other pathogens. [ABSTRACT FROM AUTHOR]

The article discusses experimental work on brown trout, Salmo trutta, with a focus on the defence of salmonid fish against zoospores of the Saprolegnia fungus. Topics include the cellular response in the fishes' external mucus, fishes' morphological response to defend against the fungal infection, and a study of diseased fish in Windermere Lake in England.

The article cites a study regarding enteric redmouth disease, which has been widely documented as a major disease of cultured salmonid fishes, primarily rainbow trout. The study reveals that a bacterium named Yersinia ruckeri cause it. Although salmonids are considered to be the primary hosts for Yersinai ruckeri increasing evidence shows a variety of non-salmonid species serving as hosts for this pathogen. The article attempts to investigate the biochemical and serological characterization of Yersinia Ruckeri.

The article reports that Tubifex tubifex is identified as the essential oligochaete in the protozoan life cycle that causes salmonid whirling disease. Actinosporean protozoans have long been recognized as parasites of annelid worms. The vertebrate phase of the whirling disease life cycle takes place in fish of the family Salmonidae. The invertebrate phase requires an oligochaete of the family Tubificidae. The purpose of the present study was to determine which of the species mentioned in the article was involved in the life cycle of the whirling disease protozoan. Assay for water-borne infectivity should not be considered definitive.

The article presents information on cold-water vibriosis or Hitra disease in Norwegian salmonid farming. The characteristic clinical signs of the disease were extensive haemorrhages, mostly on the surfaces of internal organs, but also inside these organs and in the muscles. When these signs became apparent, the disease was apparently too far advanced to respond to antibiotic treatment. Isolates of the bacterium grown in vitro were pathogenic to rainbow trout. Two isolates were used, one from Hitra and one from Froya, both initially isolated from salmon.