BEI Inactivated Vaccine Induces Innate and Adaptive Responses and Elicits Partial Protection upon Reassortant Betanodavirus Infection in Senegalese Sole.

Yulema Valero,Carmen López-Vázquez,Carlos P Dopazo,José G Olveira,Isabel Bandín

doi:10.3390/vaccines9050458

Yulema Valero, Carmen López-Vázquez + Show 3 more

Open Access

https://doi.org/10.3390/vaccines9050458

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Journal: Vaccines	Publication Date: May 4, 2021
Citations: 18	License type: CC BY 4.0

Affiliation: University of Santiago de Compostela

Abstract

Nervous necrosis virus (NNV), the causative agent of viral encephalopathy and retinopathy (VER), is one of the most threatening viruses affecting marine and freshwater fish species worldwide. Senegalese sole is a promising fish species in Mediterranean aquaculture but also highly susceptible to NNV and VER outbreaks, that puts its farming at risk. The development of vaccines for aquaculture is one of best tools to prevent viral spread and sudden outbreaks, and virus inactivation is the simplest and most cost-effective method available. In this work, we have designed two inactivated vaccines based on the use of formalin or binary ethylenimine (BEI) to inactivate a reassortant NNV strain. After vaccination, the BEI-inactivated vaccine triggered the production of specific IgM-NNV antibodies and stimulated innate and adaptive immune responses at transcriptional level (rtp3, mx, mhcii and tcrb coding genes). Moreover, it partially improved survival after an NNV in vivo challenge, reducing the mid-term viral load and avoiding the down-regulation of immune response post-challenge. On the other hand, the formalin-inactivated vaccine improved the survival of fish upon infection without inducing the production of IgM-NNV antibodies and only stimulating the expression of herc4 and mhcii genes (in head-kidney and brain, respectively) during the vaccination period; this suggests that other immune-related pathways may be involved in the partial protection provoked. Although these vaccines against NNV showed encouraging results, further studies are needed to improve sole protection and to fully understand the underlying immune mechanism.

Highlights

Aquaculture is one of the fastest growing sectors of the food industry worldwide
Complete formalin inactivation was achieved after nine days of incubation since neither cytopathic effect (CPE) nor viral titer were recorded after three blind passages (Table 2)
Our first observation was that the complete inactivation of nervous necrosis virus (NNV) was achieved with 0.2% formalin or 1 mM binary ethylenimine (BEI) after 9 days or 72 h of incubation, respectively

Summary

Introduction

Aquaculture is one of the fastest growing sectors of the food industry worldwide. Nowadays, global aquaculture has surpassed marine catches in terms of fish protein production for human consumption [1]. As a result of this growth, the spread of viruses has risen, due to the constant transport of eggs and larvae between fish farms all over the world and because survivors of an epizootic outbreak often become asymptomatic carriers. NNV is the causative agent of viral encephalopathy and retinopathy (VER), a neuropathological condition which provokes mortality rates of up to 100%, at early stages of development (larvae and juveniles), especially in marine fish [2]. Natural reassortants between RGNNV and SJNNV genotypes have been isolated as the causative agents of disease outbreaks in different species, including sole (Solea sp.) and gilthead seabream (Sparus aurata), the latter previously thought to be an asymptomatic NNV carrier [3,4,5,6]

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