Search Results (7)

Gilthead sea bream and European sea bass display different resistance–susceptibility patterns during infection with different nervous necrosis virus (NNV) species, which may derive from differences in the triggered immune response. Based on this premise, we analysed the transcription of several selected immune-related genes in sea bream experimentally infected with NNV isolates obtained from sea bass (DlNNV, RGNNV) or sea bream (SaNNV, RGNNV/SJNNV). Viral replication only occurred in SaNNV-inoculated fish; therefore, the differences between the immune response elicited by both viruses may be the key to understanding the mechanism behind the inhibition of DlNNV replication. Principal component analysis clustered samples according to the viral isolate from 1 day post infection onwards and evidenced differences in the immune response against both viruses, even though no mortalities or symptoms were recorded. The response against DlNNV is characterized by higher rtp3 transcription early after the infection, longer-lasting il-10 transcription and stronger induction of casp1 and hsp70. These genes should be targets for future studies in order to elucidate their role in hampering NNV replication in sea bream, which is essential for developing effective prophylactic measures. Full article

Aquaculture is the fastest-growing food-producing sector, with a global production of 122.6 million tonnes in 2020. Nonetheless, aquatic animal production can be hampered by the occurrence of viral diseases. Furthermore, intensive farming conditions and an increasing number of reared fish species have boosted the number of aquatic animals’ pathogens that researchers have to deal with, requiring the quick development of new detection and study methods for novel unknown pathogens. In this respect, the molecular tools have significantly contributed to investigating thoroughly the structural constituents of fish viruses and providing efficient detection methods. For instance, next-generation sequencing has been crucial in reassignment to the correct taxonomic family, the sturgeon nucleo-cytoplasmic large DNA viruses, a group of viruses historically known, but mistakenly considered as iridoviruses. Further methods such as in situ hybridisation allowed objectifying the role played by the pathogen in the determinism of disease, as the cyprinid herpesvirus 2, ostreid herpesvirus 1 and betanodaviruses. Often, a combination of molecular techniques is crucial to understanding the viral role, especially when the virus is detected in a new aquatic animal species. With this paper, the authors would critically revise the scientific literature, dealing with the molecular techniques employed hitherto to study the most relevant finfish and shellfish viral pathogens. Full article

The production of the aquaculture industry has increased to be equal to that of the world fisheries in recent years. However, aquaculture production faces threats such as infectious diseases. Betanodaviruses induce a neurological disease that affects fish species worldwide and is caused by nervous necrosis virus (NNV). NNV has a nude capsid protecting a bipartite RNA genome that consists of molecules RNA1 and RNA2. Four NNV strains distributed worldwide are discriminated according to sequence homology of the capsid protein encoded by RNA2. Since its first description over 30 years ago, the virus has expanded and reassortant strains have appeared. Preventive treatments prioritize the RGNNV (red-spotted grouper nervous necrosis virus) strain that has the highest optimum temperature for replication and the broadest range of susceptible species. There is strong concern about the spreading of NNV in the mariculture industry through contaminated diet. To surveil natural reservoirs of NNV in the western Mediterranean Sea, we collected invertebrate species in 2015 in the Alboran Sea. We report the detection of the RGNNV strain in two species of cephalopod mollusks (Alloteuthis media and Abralia veranyi), and in one decapod crustacean (Plesionika heterocarpus). According to RNA2 sequences obtained from invertebrate species and reported to date in the Mediterranean Sea, the strain RGNNV is predominant in this semienclosed sea. Neither an ecosystem- nor host-driven distribution of RGNNV were observed in the Mediterranean basin. Full article

Nervous necrosis virus (NNV) has been responsible for mass mortalities in the aquaculture industry worldwide, with great economic and environmental impact. The present review aims to summarize the current knowledge of gene expression responses to nervous necrosis virus infection in different fish species based on transcriptomic analysis data. Four electronic databases, including PubMed, Web of Science, and SCOPUS were searched, and more than 500 publications on the subject were identified. Following the application of the appropriate testing, a total of 24 articles proved eligible for this review. NNV infection of different host species, in different developmental stages and tissues, presented in the eligible publications, are described in detail, revealing and highlighting genes and pathways that are most affected by the viral infection. Those transcriptome studies of NNV infected fish are oriented in elucidating the roles of genes/biomarkers for functions of special interest, depending on each study’s specific emphasis. This review presents a first attempt to provide an overview of universal host reaction mechanisms to viral infections, which will provide us with new perspectives to overcome NNV infection to build healthier and sustainable aquaculture systems. Full article

Nervous necrosis virus (NNV), genus Betanodavirus, the etiological agent of the viral encephalopathy and retinopathy (VER), presents a genome with two positive-sense single-stranded RNA segments. Striped jack nervous necrosis virus (SJNNV) and red-spotted grouper nervous necrosis virus (RGNNV), together with reassortants RGNNV/SJNNV, are the betanodaviruses predominantly isolated in Southern Europe. An RGNNV/SJNNV reassortant isolated from Senegalese sole (wt160) causes high mortalities in this fish species. This virus presents differences in the sequence of the 3’ non-coding region (NCR) of both segments compared to RGNNV and SJNNV reference strains. Previously, it has been reported that the reversion of two of these differences (nucleotides 1408 and 1412) in the RNA2 3’NCR to the SJNNV-type (recombinant r1408-1412) resulted in a decrease in sole mortality. In the present study, we have applied an OpenArray^® to analyse the involvement of sole immune response in the virulence of several recombinants: the r1408-1412 and two recombinants, developed in the present study, harbouring mutations at positions 3073 and 3093 of RNA1 3’NCR to revert them to RGNNV-type. According to the correlation values and to the number of expressed genes, the infection with the RNA2-mutant provoked the most different immune response compared to the immune response triggered after the infection with the rest of the viruses, and the exclusive and high upregulation of genes related to the complement system. The infection with the RNA1-mutants also provoked a decrease in mortality and their replication was delayed at least 24 h compared to the wt160 replication, which could provoke the lag observed in the immune response. Furthermore, the infection with the RNA1-mutants provoked the exclusive expression of pkr and the downregulation of il17rc. Full article

Recently, three types of betanodavirus including red spotted grouper nervous necrosis virus (RGNNV), barfin flounder nervous necrosis virus (BFNNV), and Korean shellfish nervous necrosis virus (KSNNV) (proposed as a new fifth type) have been detected in shellfish in the marine environment around Korea. To investigate the presence of reassortment between betanodavirus types, the type based on the RNA2 segment of betanodaviruses carried in 420 domestic shellfish (n = 306) and finfish (n = 35), as well as imported shellfish (n = 79), was compared with the type identified by reverse-transcriptase polymerase chain reaction (RT-PCR) for RNA1 segment. Only five samples carrying reassortant betanodaviruses were found, appearing as RG/KSNNV (n = 2), KS/RGNNV (n = 1), and SJ/RGNNV (n = 2) types. From these samples, we successfully isolated two reassortant strains from Korean and Chinese shellfish in E-11 cells and called them KG1-reKS/RG and CM1-reRG/KS, respectively. In the full genome sequences, each RNA segment of the reassortant strains exhibited the same gene length and high sequence homology (≥98%) with the reference strains corresponding to the type of each segment. Both these reassortant strains induced high mortality to sevenband grouper (Epinephelus septemfasciatus) larvae with high viral concentrations in the body (10⁹ viral particles/mg) and severe vacuolation in the retina and brain. These are the first results showing the involvement of the KSNNV type in the reassortment of RNA segments in the reported types of betanodavirus, which could represent a new potential risk in fish. Full article

The growing global demand for seafood together with the limited capacity of the wild-capture sector to meet this demand has seen the aquaculture industry continue to grow around the world. A vast array of aquatic animal species is farmed in high density in freshwater, brackish and marine systems where they are exposed to new environments and potentially new diseases. On-farm stresses may compromise their ability to combat infection, and farming practices facilitate rapid transmission of disease. Viral pathogens, whether they have been established for decades or whether they are newly emerging as disease threats, are particularly challenging since there are few, if any, efficacious treatments, and the development of effective viral vaccines for delivery in aquatic systems remains elusive. Here, we review a few of the more significant viral pathogens of finfish, including aquabirnaviruses and infectious hematopoietic necrosis virus which have been known since the first half of the 20th century, and more recent viral pathogens, for example betanodaviruses, that have emerged as aquaculture has undergone a dramatic expansion in the past few decades. Full article