Abstract
Viral nervous necrosis (VNN) caused by the nervous necrosis virus (NNV) affects a broad range of primarily marine fish species, with mass mortality rates often seen among larvae and juveniles. Its genetic diversification may hinder the effective implementation of preventive measures such as vaccines. The present study describes different inactivation procedures for developing an inactivated vaccine against a new NNV isolate confirmed to possess deadly effects upon the European seabass (Dicentrarchus labrax), an important Mediterranean farmed fish species that is highly susceptible to this disease. First, an NNV isolate from seabass adults diagnosed with VNN was rescued and the sequences of its two genome segments (RNA1 and RNA2) were classified into the red-spotted grouper NNV (RGNNV) genotype, closely clustering to the highly pathogenic 283.2009 isolate. The testing of different inactivation procedures revealed that the virus particles of this isolate showed a marked resistance to heat (for at least 60 °C for 120 min with and without 1% BSA) but that they were fully inactivated by 3 mJ/cm2 UV-C irradiation and 24 h 0.2% formalin treatment, which stood out as promising NNV-inactivation procedures for potential vaccine candidates. Therefore, these procedures are feasible, effective, and rapid response strategies for VNN control in aquaculture.
Highlights
The scarcity of alternative therapeutics against viral infections that are as efficient as vaccines makes them essential in such areas as animal care [1]
All brain tissue samples, which were obtained from the three seabass individuals showing typical Viral nervous necrosis (VNN) pathological symptoms, induced classically in vitro nervous necrosis virus (NNV) cytopathogenic effect (CPE)
Parallel in vitro assays confirmed NNV as the causative agent of the mentioned symptoms/effects, since single PCR products with expected lengths were amplified with specific primers for genes from both NNV genome fragments
Summary
The scarcity of alternative therapeutics against viral infections that are as efficient as vaccines makes them essential in such areas as animal care [1]. Whole-pathogen vaccines consist of liveattenuated or weakened microorganisms, which usually yield improved immunological assets versus killed or inactivated microorganisms In comparison, the latter presents substantial biosafety and handling advantages [2] and a higher market acceptance in the animal production industry, including aquaculture [3,4,5,6,7]. The overall production procedure used for all virus-inactivated vaccines consists of harvesting large amounts of viral particles (often purified and concentrated) and their subsequent inactivation by chemical and/or physical methods [8] In this sense, several inactivation agents have been reported to be successful for this purpose, including many examples for fish viral pathogens. To the best of our knowledge, only formalin has been used for the inactivation of licensed fish viral vaccines [3,4,6]
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