Vaccination with recombinant protein (r22C03), a putative attachment factor of Neoparamoeba perurans, against AGD in Atlantic salmon (Salmo salar) and implications of a co-infection with Yersinia ruckeri

Inoculation of Freund's adjuvant in European eel (Anguilla anguilla) revealed key KEGG pathways and DEGs of host anti-Edwardsiella anguillarum infection

Freund's complete (FCA) and incomplete adjuvants (FIA), generally applied in subunit fishery vaccine, have not been explored on the molecular mechanism of the nonspecific immune enhancement. In this study, we examined the RNA-seq in the spleen of European eel (Anguilla anguilla) inoculated with FCA and FIA (FCIA group) to elucidate the key KEGG pathways and differential expressed genes (DEGs) in the process of Edwardsiella anguillarum infection and A. anguilla anti-E. anguillarum infection using genome-wide transcriptome. After eels were challenged by E. anguillarum at 28 d post the first inoculation (dpi), compared to the control uninfected eels (Con group), the control infected eels (Con_inf group) showed severe pathological changes in the liver, kidney and spleen, although infected eels post the inoculation of FCIA (FCIA_inf group) also formed slight bleeding. Compared to the FCIA_inf group, there was more than 10 times colony forming unit (cfu) in the Con_inf group per 100 μg spleen, kidney or blood, and the relative percent survival (RPS) of eels was 44.4% in FCIA_inf vs Con_inf. Compared to the Con group, the SOD activity in the FCIA group increased significantly in the liver and spleen. Using high-throughput transcriptomics, DEGs were identified and 29 genes were verified using fluorescence real-time polymerase chain reaction (qRT-PCR). The result of DEGs clustering showed 9 samples in 3 groups of Con, FCIA and FCIA_inf were similar, contrast to distinct differences of 3 samples in the Con_inf group. We found 3795 up and 3548 down regulated DEGs in the compare of FCIA_inf vs Con_inf, of which 5 enriched KEGG pathways of "Lysosome", "Autophagy", "Apoptosis", "C-type lectin receptor signaling" and "Insulin signaling" were ascertained, and 26 of 30 top GO terms in the compare were significantly enriched. Finally, protein-protein interactions between the DEGs of the 5 KEGG pathways and other DEGs were explored using Cytoscape 3.9.1. The compare of FCIA_inf vs Con_inf showed 110 DEGs from the 5 pathways and 718 DEGs from other pathways formed total of 9747° in a network, of which 9 hub DEGs play vital roles in anti-infection or apoptosis. Together, the interaction networks revealed that 9 DEGs involved in the 5 pathways underlies the key process of A. anguilla anti-E. anguillarum infection or host cell apoptosis.

Comparative transcriptome profiling of virulent and avirulent isolates of Neoparamoeba perurans

Neoparamoeba perurans, the aetiological agent of amoebic gill disease, remains a persistent threat to Atlantic salmon mariculture operations worldwide. Innovation in methods of AGD control is required yet constrained by a limited understanding of the mechanisms of amoebic gill disease pathogenesis. In the current study, a comparative transcriptome analysis of two N. perurans isolates of contrasting virulence phenotypes is presented using gill-associated, virulent (wild type) isolates, and in vitro cultured, avirulent (clonal) isolates. Differential gene expression analysis identified a total of 21,198 differentially expressed genes between the wild type and clonal isolates, with 5674 of these genes upregulated in wild type N. perurans. Gene set enrichment analysis predicted gene sets enriched in the wild type isolates including, although not limited to, cortical actin cytoskeleton, pseudopodia, phagocytosis, macropinocytic cup, and fatty acid beta-oxidation. Combined, the results from these analyses suggest that upregulated gene expression associated with lipid metabolism, oxidative stress response, protease activity, and cytoskeleton reorganisation is linked to pathogenicity in wild type N. perurans. These findings provide a foundation for future AGD research and the development of novel therapeutic and prophylactic AGD control measures for commercial aquaculture.

Antimicrobial peptide gene expression in Atlantic salmon (Salmo salar) seven days post-challenge with Neoparamoeba perurans

Amoebic gill disease in teleost fish is caused by the marine parasite Neoparamoeba perurans. To date, the role of antimicrobial peptides β-defensins and cathelicidins in this infection have not been explored. Using a high-throughput microfluidics quantitative polymerase chain reaction system (Biomark HD™ by Fluidigm), this study aimed to: firstly, to investigate organ-specific expression of antimicrobial peptide genes β-defensin-1, -3 and -4 and cathelicidin 2 in healthy Atlantic salmon; secondly, to compare the expression of these antimicrobial peptide genes in healthy versus asymptomatic Atlantic salmon seven days post-challenge with Neoparamoeba perurans. Results from this study indicate expression of the β-defensin and cathelicidin genes in the selected organs from healthy Atlantic salmon. Furthermore, a statistically significant upregulation of β-defensins -3 and -4 and cathelicidin 2 was detected in gill of parasite-challenged salmon. The upregulated cathelicidin and β-defensin genes in gill could indicate novel potential roles in innate immune responses to Neoparamoeba perurans.

Long-term efficacy of nasal vaccination against enteric red mouth (ERM) disease and infectious hematopoietic necrosis (IHN) in juvenile rainbow trout (Oncorhynchus mykiss)

Previous research demonstrated that bacterial and viral vaccines delivered via the nasal route in rainbow trout (Oncorhynchus mykiss) at 7 and 28 days post-vaccination are highly protective (>95% protection). Long-term protection following nasal vaccination in teleosts has not been evaluated. The goal of this study was to assess efficacy and immune responses at 6 months (mo) post-vaccination (mpv), and long-lasting immune responses at 12 mpv of two different vaccines: an inactivated enteric red mouth disease (ERM) Yersinia ruckeri bacterin and a live attenuated infectious hematopoietic necrosis virus (IHNV) vaccine. Juvenile rainbow trout were vaccinated for Y. ruckeri via intraperitoneal (I.P.) and intranasal (I.N.) routes, and for IHNV by intramuscular (I.M.) and I.N. routes, then challenged at 6 mpv. Immune responses were determined at 6 and 12 mpv. ERM vaccine I.P. delivery elicited significantly higher serum IgM-specific titers that remained elevated compared to mock-vaccinated fish at 6 mpv. By 12 mpv, antibody titers to Y. ruckeri were not significantly different across all treatments. Following Y. ruckeri challenge at 6 mpv, a significant difference in cumulative percent mortality (CPM) was found for I.P.-vaccinated fish but not I.N.-vaccinated fish. I.M. and I.N. vaccination with live attenuated IHNV did not result in significant specific serum IgM titers at 6 or 12 mpv. Yet, I.N.-vaccinated fish showed the lowest CPM 6 mpv indicating long-term protection that does not correlate with systemic IgM responses. Repertoire analyses confirmed unique expansions of VH-JH rearrangements in the spleen of rainbow trout 12 mpv that varied with the type of vaccine and route of vaccination. Combined, these data demonstrate that I.N. vaccination with a live attenuated viral vaccine confers long lasting protection, but I.N. ERM vaccination does not and booster before 6 mpv is recommended.

State-of-the-Art Vaccine Research for Aquaculture Use: The Case of Three Economically Relevant Fish Species

In the last three decades, the aquaculture sector has experienced a 527% growth, producing 82 million tons for a first sale value estimated at 250 billion USD. Infectious diseases caused by bacteria, viruses, or parasites are the major causes of mortality and economic losses in commercial aquaculture. Some pathologies, especially those of bacterial origin, can be treated with commercially available drugs, while others are poorly managed. In fact, despite having been recognized as a useful preventive measure, no effective vaccination against many economically relevant diseases exist yet, such as for viral and parasitic infections. The objective of the present review is to provide the reader with an updated perspective on the most significant and innovative vaccine research on three key aquaculture commodities. European sea bass (Dicentrarchus labrax), Nile tilapia (Oreochromis niloticus), and Atlantic salmon (Salmo salar) were chosen because of their economic relevance, geographical distinctiveness, and representativeness of different culture systems. Scientific papers about vaccines against bacterial, viral, and parasitic diseases will be objectively presented; their results critically discussed and compared; and suggestions for future directions given.

Integration of Transcriptome, Gross Morphology and Histopathology in the Gill of Sea Farmed Atlantic Salmon (Salmo salar): Lessons From Multi-Site Sampling

The gill of teleost fish is a multifunctional organ involved in many physiological processes such as gas exchange, osmotic and ionic regulation, acid-base balance and excretion of nitrogenous waste. Due to its extensive interface with the environment, the gill plays a key role as a primary mucosal defense tissue against pathogens, as manifested by the presence of the gill-associated lymphoid tissue (GIALT). In recent years, the prevalence of multifactorial gill pathologies has increased significantly, causing substantial losses in Atlantic salmon aquaculture. The transition from healthy to unhealthy gill phenotypes and the progression of multifactorial gill pathologies, such as proliferative gill disease (PGD), proliferative gill inflammation (PGI) and complex gill disorder (CGD), are commonly characterized by epithelial hyperplasia, lamellar fusion and inflammation. Routine monitoring for PGD relies on visual inspection and non-invasive scoring of the gill tissue (gross morphology), coupled with histopathological examination of gill sections. To explore the underlying molecular events that are associated with the progression of PGD, we sampled Atlantic salmon from three different marine production sites in Scotland and examined the gill tissue at three different levels of organization: gross morphology with the use of PGD scores (macroscopic examination), whole transcriptome (gene expression by RNA-seq) and histopathology (microscopic examination). Our results strongly suggested that the changes in PGD scores of the gill tissue were not associated with the changes in gene expression or histopathology. In contrast, integration of the gill RNA-seq data with the gill histopathology enabled us to identify common gene expression patterns associated with multifactorial gill disease, independently from the origin of samples. We demonstrated that the gene expression patterns associated with multifactorial gill disease were dominated by two processes: a range of immune responses driven by pro-inflammatory cytokines and the events associated with tissue damage and repair, driven by caspases and angiogenin.

Immunity induced by recombinant attenuated IHNV (infectious hematopoietic necrosis virus)-GN438A expresses VP2 gene-encoded IPNV (infectious pancreatic necrosis virus) against both pathogens in rainbow trout

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are important pathogens in rainbow trout farming worldwide. Their co-infection is also common, which causes great economic loss in juvenile salmon species. Development of a universal virus vaccine providing broadly cross-protective immunity will be of great importance. In this study, we generated two recombinant (r) virus (rIHNV-N438A-ΔNV-EGFP and rIHNV-N438A-ΔNV-VP2) replacing the NV gene of the backbone of rIHNV at the single point mutation at residue 438 with an efficient green fluorescent protein (EGFP) reporter gene and antigenic VP2 gene of IPNV. Meanwhile, we tested their efficacy against the wild-type (wt) IHNV HLJ-09 virus and IPNV serotype Sp virus challenge. The relative per cent survival rates of two recombinant viruses against (wt) IHNV HLJ-09 virus challenge were 84.6% and 81.5%, respectively. Simultaneously, the relative per cent survival rate of rIHNV-N438A-ΔNV-VP2 against IPNV serotype Sp virus challenge was 88.9%. It showed the two recombinant viruses had high protection rates and induced a high level of antibodies against IHNV or IPNV. Taken together, these results suggest the VP2 gene of IPNV can act as candidate gene for vaccine and attenuated multivalent live vaccines and molecular marker vaccines have potential application for viral vaccine.

Recombinant infectious hematopoietic necrosis virus expressing infectious pancreatic necrosis virus VP2 protein induces immunity against both pathogens

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are typical pathogens of rainbow trout. Their co-infection is also common, which causes great economic loss in juvenile salmon species. Although vaccines against IHNV and IPNV have been commercialized in many countries, the prevalence of IHNV and IPNV is still widespread in modern aquaculture. In the present study, two IHNV recombinant viruses displaying IPNV VP2 protein (rIHNV-IPNV VP2 and rIHNV-IPNV VP2COE) were generated using the RNA polymerase Ⅱ system to explore the immunogenicity of IHNV and IPNV. The recombinant IHNV viruses were stable, which was confirmed by sequencing, indirect immunofluorescence assay, western blotting, transmission electron microscopy and viral growth curve assay. IHNV and IPNV challenge showed that the recombinant viruses had high protection rates against IHNV and IPNV with approximately 65% relative percent survival rates. Rainbow trout (mean weight 20 g) vaccinated with these two recombinant viruses showed a high level of antibodies against IHNV and IPNV infection. Taken together, our findings demonstrate that rIHNV-IPNV VP2 and rIHNV-IPNV VP2COE might be promising vaccine candidates against IHNV and IPNV.

Bivalent DNA vaccine induces significant immune responses against infectious hematopoietic necrosis virus and infectious pancreatic necrosis virus in rainbow trout

Infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) are important pathogens of salmon and trout. An active bivalent DNA vaccine was constructed with the glycoprotein gene of Chinese IHNV isolate Sn1203 and VP2-VP3 gene of Chinese IPNV isolate ChRtm213. Rainbow trout (5 g) were vaccinated by intramuscular injection with 1.0 µg of the bivalent DNA vaccine and then challenged with an intraperitoneal injection of IHNV, IPNV, or both, at 30 and 60 days post-vaccination (d.p.v.). High protection rates against IHNV were observed, with 6% and 10% cumulative mortality, respectively, compared with 90-94% in the mock-vaccinated groups. IPNV loads (531-fold and 135-fold, respectively) were significantly reduced in the anterior kidneys of the vaccinated trout. Significant protection against co-infection with IHNV and IPNV was observed, with cumulative mortality rates of 6.67% and 3.33%, respectively, compared with 50.0% and 43.3%, respectively, in the mock-vaccinated groups. No detectable infective IHNV or IPNV was recovered from vaccinated trout co-infected with IHNV and IPNV. The bivalent DNA vaccine increased the expression of Mx-1 and IFN-γ at 4, 7, and 15 d.p.v, and IgM at 21 d.p.v., and induced high titres (≥160) of IHNV and IPNV neutralizing antibodies at 30 and 60 d.p.v.