Infectious agents and their physiological correlates in early marine Chinook salmon (Oncorhynchus tshawytscha).

The early marine life of Pacific salmon is believed to be a critical period limiting population-level survival. Recent evidence suggests that some infectious agents are associated with survival but linkages with underlying physiological mechanisms are lacking. While challenge studies can demonstrate cause and effect relationships between infection and pathological change or mortality, in some cases pathological change may only manifest in the presence of environmental stressors; thus, it is important to gain context from field observations. Herein, we examined physiological correlates with infectious agent loads in Chinook salmon during their first ocean year. We measured physiology at the molecular (gene expression), metabolic (plasma chemistry) and cellular (histopathology) levels. Of 46 assayed infectious agents, 27 were detected, including viruses, bacteria and parasites. This exploratory study identified.a strong molecular response to viral disease and pathological change consistent with jaundice/anemia associated with Piscine orthoreovirus,strong molecular signals of gill inflammation and immune response associated with gill agents `Candidatus Branchiomonas cysticola' and Parvicapsula pseudobranchicola,a general downregulation of gill immune response associated with Parvicapsula minibicornis complementary to that of P. pseudobranchicola.Importantly, our study provides the first evidence that the molecular activation of viral disease response and the lesions observed during the development of the PRV-related disease jaundice/anemia in farmed Chinook salmon are also observed in wild juvenile Chinook salmon.

Assessing the role of Piscine orthoreovirus in disease and the associated risk for wild Pacific salmon.

This paper is a response to Polinski, M. P. et al. Innate antiviral defense demonstrates high energetic efficiency in a bony fish. BMC Biology 19, 138 (2021). https://doi.org/10.1186/s12915-021-01069-2.

Aquaculture mediates global transmission of a viral pathogen to wild salmon.

Global expansion of aquaculture and agriculture facilitates disease emergence and catalyzes transmission to sympatric wildlife populations. The health of wild salmon stocks critically concerns Indigenous peoples, commercial and recreational fishers, and the general public. Despite potential impact of viral pathogens such as Piscine orthoreovirus-1 (PRV-1) on endangered wild salmon populations, their epidemiology in wild fish populations remains obscure, as does the role of aquaculture in global and local spread. Our phylogeographic analyses of PRV-1 suggest that development of Atlantic salmon aquaculture facilitated spread from Europe to the North and South East Pacific. Phylogenetic analysis and reverse transcription polymerase chain reaction surveillance further illuminate the circumstances of emergence of PRV-1 in the North East Pacific and provide strong evidence for Atlantic salmon aquaculture as a source of infection in wild Pacific salmon. PRV-1 is now an important infectious agent in critically endangered wild Pacific salmon populations, fueled by aquacultural transmission.

Descriptive multi-agent epidemiology via molecular screening on Atlantic salmon farms in the northeast Pacific Ocean.

Rapid expansion of salmon aquaculture has resulted in high-density populations that host diverse infectious agents, for which surveillance and monitoring are critical to disease management. Screening can reveal infection diversity from which disease arises, differential patterns of infection in live and dead fish that are difficult to collect in wild populations, and potential risks associated with agent transmission between wild and farmed hosts. We report results from a multi-year infectious-agent screening program of farmed salmon in British Columbia, Canada, using quantitative PCR to assess presence and load of 58 infective agents (viruses, bacteria, and eukaryotes) in 2931 Atlantic salmon (Salmo salar). Our analysis reveals temporal trends, agent correlations within hosts, and agent-associated mortality signatures. Multiple agents, most notably Tenacibaculum maritimum, were elevated in dead and dying salmon. We also report detections of agents only recently shown to infect farmed salmon in BC (Atlantic salmon calicivirus, Cutthroat trout virus-2), detection in freshwater hatcheries of two marine agents (Kudoa thyrsites and Tenacibaculum maritimum), and detection in the ocean of a freshwater agent (Flavobacterium psychrophilum). Our results provide information for farm managers, regulators, and conservationists, and enable further work to explore patterns of multi-agent infection and farm/wild transmission risk.

Discovery and surveillance of viruses from salmon in British Columbia using viral immune-response biomarkers, metatranscriptomics, and high-throughput RT-PCR.

The emergence of infectious agents poses a continual economic and environmental challenge to aquaculture production, yet the diversity, abundance, and epidemiology of aquatic viruses are poorly characterised. In this study, we applied salmon host transcriptional biomarkers to identify and select fish in a viral disease state, but only those that were negative for known viruses based on RT-PCR screening. These fish were selected for metatranscriptomic sequencing to discover potential viral pathogens of dead and dying farmed Atlantic (Salmo salar) and Chinook (Oncorhynchus tshawytscha) salmon in British Columbia (BC). We found that the application of the biomarker panel increased the probability of discovering viruses in aquaculture populations. We discovered two viruses that have not previously been characterised in Atlantic salmon farms in BC (Atlantic salmon calicivirus and Cutthroat trout virus-2), as well as partially sequenced three putative novel viruses. To determine the epidemiology of the newly discovered or emerging viruses, we conducted high-throughput reverse transcription polymerase chain reaction (RT-PCR) and screened over 9,000 farmed and wild salmon sampled over one decade. Atlantic salmon calicivirus and Cutthroat trout virus-2 were in more than half of the farmed Atlantic salmon we tested. Importantly we detected some of the viruses we first discovered in farmed Atlantic salmon in Chinook salmon, suggesting a broad host range. Finally, we applied in situ hybridisation to determine infection and found differing cell tropism for each virus tested. Our study demonstrates that continual discovery and surveillance of emerging viruses in these ecologically important salmon will be vital for management of both aquaculture and wild resources in the future.

Erythroid Progenitor Cells in Atlantic Salmon (Salmo salar) May Be Persistently and Productively Infected with Piscine Orthoreovirus (PRV).

Piscine orthoreovirus (PRV-1) can cause heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar). The virus targets erythrocytes in the acute peak phase, followed by cardiomyocytes, before the infection subsides into persistence. The persistent phase is characterized by high level of viral RNA, but low level of viral protein. The origin and nature of persistent PRV-1 are not clear. Here, we analyzed for viral persistence and activity in various tissues and cell types in experimentally infected Atlantic salmon. Plasma contained PRV-1 genomic dsRNA throughout an 18-week long infection trial, indicating that viral particles are continuously produced and released. The highest level of PRV-1 RNA in the persistent phase was found in kidney. The level of PRV-1 ssRNA transcripts in kidney was significantly higher than that of blood cells in the persistent phase. In-situ hybridization assays confirmed that PRV-1 RNA was present in erythroid progenitor cells, erythrocytes, macrophages, melano-macrophages and in some additional un-characterized cells in kidney. These results show that PRV-1 establishes a productive, persistent infection in Atlantic salmon and that erythrocyte progenitor cells are PRV target cells.

Endangered wild salmon infected by newly discovered viruses.

The collapse of iconic, keystone populations of sockeye (Oncorhynchus nerka) and Chinook (Oncorhynchus tshawytscha) salmon in the Northeast Pacific is of great concern. It is thought that infectious disease may contribute to declines, but little is known about viruses endemic to Pacific salmon. Metatranscriptomic sequencing and surveillance of dead and moribund cultured Chinook salmon revealed a novel arenavirus, reovirus and nidovirus. Sequencing revealed two different arenavirus variants which each infect wild Chinook and sockeye salmon. In situ hybridisation localised arenavirus mostly to blood cells. Population surveys of >6000 wild juvenile Chinook and sockeye salmon showed divergent distributions of viruses, implying different epidemiological processes. The discovery in dead and dying farmed salmon of previously unrecognised viruses that are also widely distributed in wild salmon, emphasizes the potential role that viral disease may play in the population dynamics of wild fish stocks, and the threat that these viruses may pose to aquaculture.

Heart and skeletal muscle inflammation (HSMI) disease diagnosed on a British Columbia salmon farm through a longitudinal farm study.

Heart and skeletal muscle inflammation (HSMI) is an emerging disease of marine-farmed Atlantic Salmon (Salmo salar), first recognized in 1999 in Norway, and later also reported in Scotland and Chile. We undertook a longitudinal study involving health evaluation over an entire marine production cycle on one salmon farm in British Columbia (Canada). In previous production cycles at this farm site and others in the vicinity, cardiac lesions not linked to a specific infectious agent or disease were identified. Histologic assessments of both live and moribund fish samples collected at the farm during the longitudinal study documented at the population level the development, peak, and recovery phases of HSMI. The fish underwent histopathological evaluation of all tissues, Twort's Gram staining, immunohistochemistry, and molecular quantification in heart tissue of 44 agents known or suspected to cause disease in salmon. Our analysis showed evidence of HSMI histopathological lesions over an 11-month timespan, with the prevalence of lesions peaking at 80-100% in sampled fish, despite mild clinical signs with no associated elevation in mortalities reported at the farm level. Diffuse mononuclear inflammation and myodegeneration, consistent with HSMI, was the predominant histologic observation in affected heart and skeletal muscle. Infective agent monitoring identified three agents at high prevalence in salmon heart tissue, including Piscine orthoreovirus (PRV), and parasites Paranucleospora theridion and Kudoa thyrsites. However, PRV alone was statistically correlated with the occurrence and severity of histopathological lesions in the heart. Immunohistochemical staining further localized PRV throughout HSMI development, with the virus found mainly within red blood cells in early cases, moving into the cardiomyocytes within or, more often, on the periphery of the inflammatory reaction during the peak disease, and reducing to low or undetectable levels later in the production cycle. This study represents the first longitudinal assessment of HSMI in a salmon farm in British Columbia, providing new insights on the pathogenesis of the disease.

Comparison of captive lifespan, age-associated liver neoplasias and age-dependent gene expression between two annual fish species: Nothobranchius furzeri and Nothobranchius korthause.

Nothobranchius is a genus of annual fish broadly distributed in South-Eastern Africa and found into temporary ponds generated during the rain seasons and their lifespan is limited by the duration of their habitats. Here we compared two Nothobranchius species from radically different environments: N. furzeri and N. korthausae. We found a large difference in life expectancy (29- against 71-weeks of median life span, 40- against 80-weeks of maximum lifespan, respectively), which correlates with a diverse timing in the onset of several age dependent processes: our data show that N. korthause longer lifespan is associated to retarded onset of age-dependent liver-neoplasia and slower down-regulation of collagen 1 alpha 2 (COL1A2) expression in the skin. On the other hand, the expression of cyclin B1 (CCNB1) in the brain was strongly age-regulated, but with similar profiles in N. furzeri and N. korthausae. In conclusion, our data suggest that the different ageing rate of two species of the same genus could be used as novel tool to investigate and better understand the genetic bases of some general mechanism leading to the complex ageing process, providing a strategy to unravel some of the genetic mechanisms regulating longevity and age-associate pathologies including neoplasias.

Scuticociliatid ciliate outbreak in Australian potbellied seahorse, Hippocampus abdominalis (Lesson, 1827): clinical signs, histopathologic findings, and treatment with metronidazole.

A severe outbreak of scuticociliatosis occurred in Australian pot-bellied seahorse, Hippocampus abdominalis (Lesson, 1872), kept at the Vancouver Aquarium Marine Science Centre (Vancouver, British Columbia, Canada). Clinical signs included anorexia, lethargy, irregular respiration, and death. Cytology and histopathology revealed a high number of histophagous ciliated protozoa within the tissues. The parasite, identified as Philasterides dicentrarchi, was observed in several internal organs that appeared edematous and hemorrhagic upon postmortem examination. Severe histopathologic lesions were reported in particular in the ovary, the kidney, and the intestine. This infection was successfully treated with metronidazole via bath therapy. No further evidence of this parasite was found in the treated fish.

Photoinduced collagen cross-linking: a new approach to venous insufficiency.

BACKGROUND: What little research has been done on methods of venous valve function recovery with radiofrequency has had disappointing results. Valvuloplasty has some supporters, but the majority of physicians do not consider it a valid therapeutic option. OBJECTIVE: To test a new method of treating varicose veins based on their collagen structure. This procedure it is not a thermal treatment, but it is fast, with significant shrinking and preservation of the endothelium. MATERIALS & METHODS: In the laboratory, we subjected greater saphenous vein specimens to irradiation with a blue light-emitting diode generated (wavelength 450-480 nm) while a riboflavin solution (vitamin B2) was administered. The riboflavin acts as a cross-linking agent, and the blue light as the activator. In this photo-induced reaction, oxygen singlet is produced with oxidative deamination, forming new covalent bonds between collagen fibrils and water. RESULTS: In venous specimens, we demonstrated fast and significant shrinkaged without histologic evidence of endothelial damage and with evident change in mechanical properties of varicose veins. CONCLUSIONS: Photochemically induced collagen cross-linking to restructure varicose veins is only a research field but may become an important tool for recovery of vein diameter and valve function.

The short-lived annual fish Nothobranchius furzeri shows a typical teleost aging process reinforced by high incidence of age-dependent neoplasias.

The annual fish Nothobranchius furzeri is the shortest-lived vertebrate which can be cultured in captivity. Here, we performed a histopathological analysis of age-related lesions in this species. Post-mortem analysis revealed lesions in liver (~90%), kidney (~75%), heart (~70%) and gonads (~40%) which are similar to those previously described in the small teleost Poecilia reticulata. In addition, a high incidence of neoplasias was observed in liver (~35%) and kidney (~25%). Different laboratory strains of N. furzeri show large genetic differences in longevity. Cross-sectional analysis revealed a clear age-dependent increase in the incidence of liver neoplasias which was accelerated in a short-lived strain. Cross-sectional analysis of gonads revealed sex-specific differences in the occurrence of lesions, with males being more severely affected than females. In conclusion, our analysis demonstrates that short life span in N. furzeri is a consequence of a typical teleost aging process which determines systemic failure of homeostasis functions rather than of a single organ or apparatus. Unlike other teleosts, however, this scenario is reinforced by high incidence of age-dependent neoplasias, making this species a promising model to analyze the molecular pathways of age-dependent spontaneous tumorigenesis.