Redspotted Grouper Nervous Necrosis Virus and the Reassortant RGNNV/SJNNV In Vitro Susceptibility against a Commercial Peroxy-Acid Biocide under Different Conditions of Use

SIMPLE SUMMARY: Redspotted grouper nervous necrosis virus (RGNNV) and its reassortant strains belonging to the genus Betanodavirus represent the most threatening viral pathogens in the Mediterranean aquaculture sector. Due to the sector’s ongoing expansion, controlling the spread of viral encephalopathy and retinopathy (VER) caused by betanodaviruses is critical. For this reason, implementing strict hygienic standard procedures primarily based on disinfection could significantly reduce the spread of VER. In this study, two standardized European protocols (BS EN 14675:2015 and BS EN 17111:2018) were applied in order to assess the virucidal activity of a commercial peroxy-acid biocide against the RGNNV and its reassortant RGNNV/SJNNV strain. The disinfectant was effective in reducing the viral titer, but with different results depending on concentrations, strains, and conditions of application. ABSTRACT: Aquaculture is a constantly growing sector. The intensification of fish production and the movement of aquatic animals could cause the spread of infectious diseases. Remarkably, the diffusion of viral agents represents the major bottleneck for finfish production, and viral encephalopathy and retinopathy (VER) is considered the most impacting disease for Mediterranean aquaculture. No effective therapies are available to contrast VER, and vaccination can be applied only in grow-out facilities. Hence, programs to minimize the sanitary risks in farms are paramount to implementing hygienic standards and biosecurity. This study aimed to evaluate the in vitro virucidal activity of a peroxy-acid disinfectant (Virkon(®) S, DuPont, Sudbury, UK) towards the two NNV strains most widespread in the Mediterranean Sea. Remarkably, two protocols were applied to assess the virucidal activity under different conditions of use: the suspension test and the net test. The latter has been applied to evaluate the efficacy of the biocide on instruments, simulating the in-field application. The obtained results demonstrated the suitability of the tested biocide for NNV inactivation, being effective under some of the tested conditions. However, the presence of organic matter, the concentration of the product, and the application conditions can significantly affect the result of the disinfection procedure.