Viral encephalopathy and retinopathy (VER) disease in Epinephelus marginatus from the Balearic Islands marine protected areas

Integrated Management Strategies for Viral Nervous Necrosis (VNN) Disease Control in Marine Fish Farming in the Mediterranean

Viral nervous necrosis (VNN) is the most important viral disease affecting farmed fish in the Mediterranean. VNN can affect multiple fish species in all production phases (broodstock, hatchery, nursery and ongrowing) and sizes, but it is especially severe in larvae and juvenile stages, where can it cause up to 100% mortalities. European sea bass has been and is still the most affected species, and VNN in gilthead sea bream has become an emerging problem in recent years affecting larvae and juveniles and associated to the presence of new nervous necrosis virus (NNV) reassortants. The relevance of this disease as one of the main biological hazards for Mediterranean finfish farming has been particularly addressed in two recent H2020 projects: PerformFISH and MedAID. The presence of the virus in the environment and in the farming systems poses a serious menace for the development of the Mediterranean finfish aquaculture. Several risks associated to the VNN development in farms have been identified in the different phases of the farming system. The main risks concerning VNN affecting gilthead seabream and European seabass have been identified as restocking from wild fish in broodstock facilities, the origin of eggs and juveniles, quality water supply and live food in hatcheries and nurseries, and infected juveniles and location of farms in endemic areas for on-growing sites. Due to the potential severe impact, a holistic integrated management approach is the best strategy to control VNN in marine fish farms. This approach should include continuous surveillance and early and accurate diagnosis, essential for an early intervention when an outbreak occurs, the implementation of biosecurity and disinfection procedures in the production sites and systematic vaccination with effective vaccines. Outbreak management practices, clinical aspects, diagnostic techniques, and disinfections methods are reviewed in detail in this paper. Additionally, new strategies are becoming more relevant, such as the use of genetic resistant lines and boosting the fish immune system though nutrition.

Detection of RGNNV genotype betanodavirus in the Black Sea and monitoring studies

Viral nervous necrosis (VNN), caused by betanodavirus, is a significant viral infection that threatens marine aquaculture. Freshwater and marine fish farms in Turkey are subjected to annual pathogen screenings. In 2016, during the Nervous Necrosis Virus screening program conducted in the Black Sea, betanodavirus was unexpectedly detected using real-time reverse transcription-polymerase chain reaction in apparently healthy sea bass. Phylogenetic analysis of both the RNA1 and RNA2 segments of the virus determined that the betanodavirus detected was red-spotted grouper nervous necrosis virus genotype (RGNNV). Following the initial discovery of betanodavirus in the Black Sea, monitoring studies performed over a 3 yr period have not indicated any additional presence of the virus. The absence of clinical symptoms related to VNN disease in the area's marine fish farms and the surrounding detection zone, and the fact that the virus has not been detected anew in monitoring programmes conducted following the initial detection, indicate that there is no virus circulation in the detection zone.

Viral encephalopathy and retinopathy is endemic in wild groupers (genus Epinephelus spp.) of the Algerian coast

This work describes betanodavirus infection in two species of groupers (family Serranidae) from the Algerian coast: the dusky grouper Epinephelus marginatus and the golden grouper Epinephelus costae. At necropsy, characteristic clinical signs, external injuries, clouded eyes and brain congestion, generally associated with viral encephalopathy and retinopathy (VER) infection were observed. The partial sequences of RNA1 and RNA2 from two viral strains were obtained, and the phylogenetic analysis revealed the presence of the red-spotted grouper nervous necrosis virus (RGNNV) genotype closely related to strains previously detected in groupers in the same geographic area. Results obtained in this study support the hypothesis that VER disease is endemic in the Algerian grouper population.

Betanodavirus and VER Disease: A 30-year Research Review

The outbreaks of viral encephalopathy and retinopathy (VER), caused by nervous necrosis virus (NNV), represent one of the main infectious threats for marine aquaculture worldwide. Since the first description of the disease at the end of the 1980s, a considerable amount of research has gone into understanding the mechanisms involved in fish infection, developing reliable diagnostic methods, and control measures, and several comprehensive reviews have been published to date. This review focuses on host–virus interaction and epidemiological aspects, comprising viral distribution and transmission as well as the continuously increasing host range (177 susceptible marine species and epizootic outbreaks reported in 62 of them), with special emphasis on genotypes and the effect of global warming on NNV infection, but also including the latest findings in the NNV life cycle and virulence as well as diagnostic methods and VER disease control.