A historical review of the key bacterial and viral pathogens of Scottish wild fish

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU)2016/429): Infection with salmonid alphavirus (SAV)

Infection with salmonid alphavirus (SAV) was assessed according to the criteria of the Animal Health Law (AHL), in particular the criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as laid out in Article 9 and Article 8 for listing animal species related to infection with SAV. The assessment was performed following the ad hoc method on data collection and assessment developed by AHAW Panel and already published. The outcome reported is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with an uncertain outcome. According to the assessment, it was uncertain whether infection with salmonid alphavirus can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (50-80% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that infection with salmonid alphavirus does not meet the criteria in Section 1 (Category A; 5-10% probability of meeting the criteria) and it is uncertain whether it meets the criteria in Sections 2, 3, 4 and 5 (Categories B, C, D and E; 50-90%, probability of meeting the criteria). The animal species to be listed for infection with SAV according to Article 8 criteria are provided.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) 2016/429): Bacterial kidney disease (BKD)

Bacterial kidney disease (BKD) was assessed according to the criteria of the Animal Health Law (AHL), in particular the criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as laid out in Article 9 and Article 8 for listing animal species related to BKD. The assessment was performed following the ad hoc method on data collection and assessment developed by AHAW Panel and already published. The outcome reported is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with an uncertain outcome. According to this assessment, BKD can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (66-90% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that BKD does not meet the criteria in Sections 1, 2 and 3 (Categories A, B and C; 1-5%, 33-66% and 33-66% probability of meeting the criteria, respectively) but meets the criteria in Sections 4 and 5 (Categories D and E; 66-90% and 66-90% probability of meeting the criteria, respectively). The animal species to be listed for BKD according to Article 8 criteria are provided.

Mangiferin and Taurine Ameliorate MSRV Infection by Suppressing NF-κB Signaling

The emergence or reemergence of viruses pose a substantial threat and challenge to the world population, livestock, and wildlife. However, the landscape of antiviral agents either for human or animal viral diseases is still underdeveloped. The far tougher actuality is the case that there are no approved antiviral drugs in the aquaculture industry, although there are diverse viral pathogens. In this study, using a novel epithelial cell line derived from the brain of Micropterus salmoides (MSBr), inflammation and oxidative stress were found to implicate the major pathophysiology of M. salmoides rhabdovirus (MSRV) through transcriptome analysis and biochemical tests. Elevated levels of proinflammatory cytokines (interleukin-1β [IL-1β], IL-6, IL-8, tumor necrosis factor alpha [TNF-α], and gamma interferon [IFN-γ]) and accumulated contents of reactive oxygen species (ROS) as well as biomarkers of oxidative damage (protein carbonyl and 8-OHdG) were observed after MSRV infection in the MSBr cells. Mangiferin or taurine dampened MSRV-induced inflammation and rescued the oxidative stress and, thus, inhibited the replication of MSRV in the MSBr cells with 50% effective concentration (EC50) values of 6.77 μg/mL and 8.02 μg/mL, respectively. Further, mangiferin or taurine hampered the activation of NF-κB1 and the NF-κB1 promoter as well as the increase of phosphorylated NF-κB (p65) protein level induced by MSRV infection, indicating their antiviral mechanism by suppressing NF-κB signaling. These findings exemplify a practice approach, aiming to dampen and redirect inflammatory responses, to develop broad-spectrum antivirals. IMPORTANCE Aquaculture now provides almost half of all fish for human food in 2021 and plays a significant role in eliminating hunger, promoting health, and reducing poverty. There are diverse viral pathogens that decrease production in aquaculture. We developed a novel epithelial cell line derived from the brain of Micropterus salmoides, which can be used for virus isolation, gene expressing, and drug screening. In this study, we focus on M. salmoides rhabdovirus (MSRV) and revealed its pathophysiology of inflammation and oxidative stress. Aiming to dampen and redirect inflammatory responses, mangiferin or taurine exhibited their antiviral capability by suppressing NF-κB signaling. Our findings exemplify a practice approach to develop broad-spectrum antivirals by dampening and redirecting inflammatory responses.

Assessing the presence and spread of Renibacterium salmoninarum between farmed and wild fish in Sweden

Bacterial kidney disease (BKD) can be a devastating bacterial infection in salmonids, and it is present in aquaculture throughout the world. BKD is caused by the Gram-positive facultative intracellular bacterium Renibacterium salmoninarum (R. salmoninarum) that is spread both horizontally and vertically. Disease signs include external ulcerations and blisters and internal signs such as organ swelling, granulomas, petechiae and ascites. In Sweden, BKD accounts for a significant income loss in aquacultures due to expensive decontamination of the facility and increased disease susceptibility for the immunocompromised fish leading to higher mortality rates. In addition, uncontrolled spread in aquaculture may threaten the survival of wild fish populations. The aim of our study was to investigate the prevalence of R. salmoninarum in wild salmonids caught in Swedish waters where net pen farms with a recent history of BKD are present. Four rivers with at least one BKD-positive or recently BKD-positive farm were selected. In addition, we evaluated the use of environmental DNA (eDNA) for surveillance and monitoring of ongoing infections at these locations. In total, 1058 fish were sampled from four different river systems, and of them 52 (4.9%) were positive for R. salmoninarum by antigen ELISA. Surprisingly, these fish were not evenly distributed between the four river systems, but 50 were caught in the same river (Ljungan). This accounts for an alarmingly high rate of 17% R. salmoninarum-positive samples in wild salmonids in this area. This number is far above what was expected and clearly shows the risk with an open farming system as well as the importance of effective health monitoring programmes to avoid an uncontrolled spread of the disease. The use of eDNA for monitoring BKD is somewhat difficult to evaluate. Few of the water samples analysed were PCR positive for R. salmoninarum (2 of 38) and those were collected where no ELISA positive fish were identified. In addition to water, sediment samples were collected under a net pen farm that had recently slaughtered all fish due to ongoing R. salmoninarum infections. Sediment samples are more promising than water as 4 of 5 samples at one farming facility where positive for R. salmoninarum. Thus, sediment samples may be valuable for monitoring potential ongoing BKD in farms, without the need to sacrifice valuable fish.

Aeromonas: the multifaceted middleman in the One Health world

Aeromonas is at the interface of all the One Health components and represents an amazingly sound test case in the One Health approach, from economic loss in aquaculture tochallenges related to antibiotic-resistant bacteria selected from the environment. In human health, infections following leech therapy is an outstanding example of such One Health challenges. Aeromonads are not only ubiquitous environmental bacteria, able to rapidly colonize and cause opportunistic infections in humans and animals, they are also capable of promoting interactions and gene exchanges between the One Health components. This makes this genus a key amplifier of genetic transfer, especially of antibiotic resistance genes.

A preliminary assessment of indirect impacts on aquaculture species health and welfare in Scotland during COVID-19 lockdown

COVID-19 led to sudden changes in human activities, mainly due to restrictive measures required to supress the virus. We assess the preliminary evidence for impacts on animal health and welfare in Scottish aquaculture, a key economic activity in remoter areas of the country. We summarise the industry structure, explore pathways of vulnerability to aquatic animal disease within a One Health framework that may be accentuated by impacts of COVID-19, and use basic routine data collection on the key welfare indicators of salmon mortality and parasitic sea lice counts. The indicators were published on schedule and provide no evidence of gross impact on health and welfare, at least for salmon, during the period of intensive lockdown restrictions in Scotland. Longer term effects cannot be ruled out and we do not assess impacts on the economic or social aspects of aquaculture production.

Nanopore whole genome sequencing and partitioned phylogenetic analysis supports a new salmonid alphavirus genotype (SAV7)

Salmon pancreas disease virus, more commonly known as salmonid alphavirus (SAV), is a single-stranded positive sense RNA virus and the causative agent of pancreas disease and sleeping disease in salmonids. In this study, a unique strain of SAV previously isolated from ballan wrasse was subjected to whole genome sequencing using nanopore sequencing. In order to accurately examine the evolutionary history of this strain in comparison to other SAV strains, a partitioned phylogenetic analysis was performed to account for variation in the rate of evolution for both individual genes and codon positions. Partitioning the genome alignments almost doubled the observed branch lengths in the phylogenetic tree when compared to the more common approach of applying one model of substitution across the genome and significantly increased the statistical fit of the best-fitting models of nucleotide substitution. Based on the genomic data, a valid case can be made for the viral strain examined in this study to be considered a new SAV genotype. In addition, this study adds to a growing number of studies in which SAV has been found to infect non-salmonid fish, and as such we have suggested that the viral species name be amended to the more inclusive 'piscine alphavirus'.

Renibacterium salmoninarum-The Causative Agent of Bacterial Kidney Disease in Salmonid Fish

Renibacterium salmoninarum is one of the oldest known bacterial pathogens of fish. This Gram-positive bacterium is the causative agent of bacterial kidney disease, a chronic infection that is mostly known to infect salmonid fish at low temperatures. Externally, infected fish can display exophthalmia as well as blebs on the skin and ulcerations alongside haemorrhages at the base of the fins and alongside the lateral line. Internally, the kidney, heart, spleen and liver can show signs of swelling. Granulomas can be seen on various internal organs, as can haemorrhages, and the organs can be covered with a false membrane. Ascites can also accumulate in the abdominal cavity. The bacterium is generally cultivated on specialized media such as kidney disease medium-1 (KDM-1), KDM-2 and selective kidney disease medium (SKDM), and a diagnostic is performed using molecular tools such as PCRs or real-time quantitative PCRs (RT-qPCRs). Several virulence mechanisms have been identified in R. salmoninarum, in particular the protein p57 that is known to play a role in both agglutination and immunosuppression of the host’s defense mechanisms. Control of the disease is difficult; the presence of asymptomatic carriers complicates the eradication of the disease, as does the ability of the bacterium to gain entrance inside the eggs. Bacterin-killed vaccines have proven to be of doubtful efficacy in controlling the disease, and even more recent application of a virulent environmental relative of R. salmoninarum is of limited efficacy. Treatment by antibiotics such as erythromycin, azithromycin and enrofloxacin can be effective but it is slow and requires prolonged treatment. Moreover, antibiotic-resistant strains have been reported. Despite being known for a long time, there is still much to be discovered about R. salmoninarum, notably regarding its virulence mechanisms and its vaccine potential. Consequently, these gaps in knowledge continue to hinder control of this bacterial disease in aquaculture settings.

Health Surveillance of Wild Brown Trout (Salmo trutta fario) in the Czech Republic Revealed a Coexistence of Proliferative Kidney Disease and Piscine Orthoreovirus-3 Infection

The population of brown trout (Salmo trutta fario) in continental Europe is on the decline, with infectious diseases confirmed as one of the causative factors. However, no data on the epizootiological situation of wild fish in the Czech Republic are currently available. In this study, brown trout (n = 260) from eight rivers were examined for the presence of viral and parasitical pathogens. Salmonid alphavirus-2, infectious pancreatic necrosis virus, piscine novirhabdovirus (VHSV) and salmonid novirhabdovirus (IHNV) were not detected using PCR. Cell culturing showed no viruses as well, and serological analysis of 110 sera did not detect any specific antibodies against VHSV or IHNV. Fish from two rivers were positive for the presence of piscine orthoreovirus-3 (PRV-3), subtype PRV-3b. However, none of the PRV-3-positive fish showed gross pathologies typically associated with PRV infections. By far the most widespread pathogen was Tetracapsuloides bryosalmonae which was confirmed in each of the examined locations, with a prevalence of up to 65% and 100%, as established by immunohistochemistry and PCR, respectively. Furthermore, up to 43.8% of fish showed signs of proliferative kidney disease caused by T. bryosalmonae, suggesting that this parasite is a main health challenge for brown trout in the Czech Republic.

Establishment of a brain cell line (FuB-1) from mummichog (Fundulus heteroclitus) and its application to fish virology, immunity and nanoplastics toxicology

The marine fish mummichog (Fundulus heteroclitus), extensively used as research model, including in ecotoxicology, for over a century has been surpassed by other fish species. This fact may be associated with the lack of cell lines from this species, excellent models for the comprehension of fish physiology, immunology, toxicology and virology, that contribute to the reduction in the number of animals used in research. We have generated, for the first time, a brain-derived cell line from mummichog, FuB-1, and evaluated its application to the fields of fish virology, immunity and toxicology. First, FuB-1 cells show epithelial morphology and neural stem/astroglial origin. Secondly, FuB-1 cells effectively supports the replication of both spring viremia carp (SVCV) and infectious pancreatic necrosis (IPNV) viruses, but not nodavirus (NNV), indicating its potential use for fish virology. Related to this, FuB-1 cells infected with NNV up-regulate the transcription of genes related to the antiviral immune response, leading to cell resistance; while they are unaltered when infected with IPNV and SVCV, facilitating viral replication. Finally, FuB-1 cells were used for toxicological purposes and we demonstrated that exposure to either polystyrene nanoplastics (PS-100) or several human-usage pharmaceuticals are cytotoxic. Additionally, PS-100 particles increase the antioxidant catalase and glutathione S-transferase activities and decrease the total non-protein thiols in FuB-1 cells. However, PS-100 particles are able to reduce the cytotoxic effects induced by the pharmaceuticals. In conclusion, we have generated a cell line from mummichog, which might represent a valuable model for fish studies in the fields of virology, immunology and toxicology.

Exploring small cationic peptides of different origin as potential antimicrobial agents in aquaculture

Antimicrobial peptides (AMPs) form part of the innate immune response, which is of vital importance in fish, especially in eggs and early larval stages. Compared to antibiotics, AMPs show action against a wider spectrum of pathogens, including viruses, fungi and parasites, are more friendly to the environment, and do not seem to generate resistance in bacteria. Thus, we have tested in vitro the potential use of several synthetic peptides as antimicrobial agents in aquaculture: frog Caerin1.1, European sea bass Dicentracin (Dic) and NK-lysin peptides (NKLPs) and sole NKLP27. Our results demonstrate that the highest bactericidal activity against both human and fish pathogens was obtained with Caerin1.1 followed by sea bass Dic and NKLPs, having the sea bass NKLP20.2 none to negligible activity. Interestingly, Aeromonas salmonicida was refractory to all the fish peptides tested. Regarding the antiviral activity, synthetic peptides were able to inhibit the viral infection of nodavirus (NNV), viral septicaemia haemorrhagic virus (VHSV), infectious pancreatic necrosis virus (IPNV) and spring viremia carp virus (SVCV), which are some of the most devastating virus for aquaculture. However, their effectiveness was highly dependent on the type of virus. Strikingly, IPNV resulted the most resistant virus since Caeerin1.1 and sea bass NKLP20.2 were unable to reduce its titre and the other peptides tested only reduced it to values in the 43-78% range. These data demonstrate that synthetic peptides have great antibacterial and antiviral in vitro activity against important fish pathogens and point to their use as potential therapeutic agents in aquaculture.

The Infectious Pancreatic Necrosis Virus (IPNV) and its Virulence Determinants: What is Known and What Should be Known

Infectious pancreatic necrosis (IPN) is a disease of great concern in aquaculture, mainly among salmonid farmers, since losses in salmonid fish—mostly very young rainbow trout (Salmo gairdnery) fry and Atlantic salmon (Salmo salar) post-smolt—frequently reach 80–90% of stocks. The virus causing the typical signs of the IPN disease in salmonids, named infectious pancreatic necrosis virus (IPNV), has also been isolated from other fish species either suffering related diseases (then named IPNV-like virus) or asymptomatic; the general term aquabirnavirus is used to encompass all these viruses. Aquabirnaviruses are non-enveloped, icosahedral bisegmented dsRNA viruses, whose genome codifies five viral proteins, three of which are structural, and one of them is an RNA-dependent RNA polymerase. Due to the great importance of the disease, there have been great efforts to find a way to predict the level of virulence of IPNV isolates. The viral genome and proteins have been the main focus of research. However, to date such a reliable magic marker has not been discovered. This review describes the processes followed for decades in the attempts to discover the viral determinants of virulence, and to help the reader understand how viral components can be involved in virulence modulation in vitro and in vivo. There is also a brief description of the disease, of host defenses, and of the molecular structure and function of the virus and its viral components.

Review of infectious agent occurrence in wild salmonids in British Columbia, Canada

Wild Pacific salmonids (WPS) are economically and culturally important to the Pacific North region. Most recently, some populations of WPS have been in decline. Of hypothesized factors contributing to the decline, infectious agents have been postulated to increase the risk of mortality in Pacific salmon. We present a literature review of both published journal and unpublished data to describe the distribution of infectious agents reported in wild Pacific salmonid populations in British Columbia (BC), Canada. We targeted 10 infectious agents, considered to potentially cause severe economic losses in Atlantic salmon or be of conservation concern for wild salmon in BC. The findings indicated a low frequency of infectious hematopoietic necrosis virus, piscine orthoreovirus, viral haemorrhagic septicaemia virus, Aeromonas salmonicida, Renibacterium salmoninarum, Piscirickettsia salmonis and other Rickettsia-like organisms, Yersinia ruckeri, Tenacibaculum maritimum and Moritella viscosa. No positive results were reported for infestations with Paramoeba perurans in peer-reviewed papers and the DFO Fish Pathology Program database. This review synthesizes existing information, as well as gaps therein, that can support the design and implementation of a long-term surveillance programme of infectious agents in wild salmonids in BC.

Effects of a phytogenic, alone and associated with potassium diformate, on tilapia growth, immunity, gut microbiome and resistance against francisellosis

This work evaluated the effects of dietary supplementation of A-Live (phytogenic) either individually or in combination with Aquaform (potassium diformate, acidifier) on juvenile Nile tilapia (Oreochromis niloticus) growth performance, innate immune parameters, gut microbiome, and resistance against Francisella noatunensis subsp. orientalis challenge. Each experimental group contained 140 fishes (34.3 ± 0.33) in two 150L tanks. The experimental design consisted of five groups: a negative control; treated groups (G1, G2, G3) supplemented with different concentrations of A-Live and Aquaform in the feed; and a positive control (PC) for pathogen infection. Groups G1, G2, G3, and PC were challenged with Francisella spp. after 15 days. After infection, the mortality was significantly lower in groups G1, G2, and G3 (p < 0.01). Furthermore, these groups showed significant increase (p < 0.05) in daily weight gain, feed conversion rate, and specific growth rate. The PC group presented increase (p < 0.05) in the leukocytes and neutrophils number. Innate immunity parameters showed no difference between treatments after infection. Microbiome analysis revealed an increased number of bacteria belonging to the Vibrionaceae family after pathogen infection suggesting a secondary pathogen function of these bacteria. These results validate the beneficial effects of these products in tilapia farming.

Molecular epidemiological study on Infectious Pancreatic Necrosis Virus isolates from aquafarms in Scotland over three decades

In order to obtain an insight into genomic changes and associated evolution and adaptation of Infectious Pancreatic Necrosis Virus (IPNV), the complete coding genomes of 57 IPNV isolates collected from Scottish aquafarms from 1982 to 2014 were sequenced and analysed. Phylogenetic analysis of the sequenced IPNV strains showed separate clustering of genogroups I, II, III and V. IPNV isolates with genetic reassortment of segment A/B of genogroup III/II were determined. About 59 % of the IPNV isolates belonged to the persistent type and 32 % to the low-virulent type, and only one highly pathogenic strain (1.79 %) was identified. Codon adaptation index calculations indicated that the IPNV major capsid protein VP2 has adapted to its salmonid host. Under-representation of CpG dinucleotides in the IPNV genome to minimize detection by the innate immunity receptors, and observed positive selection in the virulence determination sites of VP2 embedded in the variable region of the main antigenic region, suggest an immune escape mechanism driving virulence evolution. The prevalence of mostly persistent genotypes, together with the assumption of adaptation and immune escape, indicates that IPNV is evolving with the host.

Discovery of nonnucleoside inhibitors of polymerase from infectious pancreatic necrosis virus (IPNV)

Introduction

Infectious pancreatic necrosis virus (IPNV) causes serious losses in several fish species of commercial interest. IPNV is a non-enveloped double-stranded RNA virus with a genome consisting of two segments A and B. Segment B codes for the VP1 protein, a non-canonical RNA-dependent RNA polymerase that can be found both in its free form and linked to the end of genomic RNA, an essential enzyme for IPNV replication.

Materials and methods

We take advantage of the knowledge over the allosteric binding site described on the surface of the thumb domain of Hepatitis C virus (HCV) polymerase to design new non-nucleoside inhibitors against the IPNV VP1 polymerase.

Results

Molecular docking techniques have been used to screen a chemical library of 23,760 compounds over a defined cavity in the surface of the thumb domain. Additional ADMET (absorption, distribution, metabolism, excretion, and toxicity) filter criteria has been applied.

Conclusion

We select two sets of 9 and 50 inhibitor candidates against the polymerases of HCV and IPNV, respectively. Two non-toxic compounds have been tested in vitro with antiviral capacity against IPNV Sp and LWVRT60 strains in the low µM range with different activity depending on the IPNV strain used.