One of the most relevant infectious diseases affecting farmed fish is the viral encephalopathy and retinopathy, caused by the nervous necrosis virus (NNV). The two commercial vaccines available against this virus have been designed to protect European seabass against the infection with a particular NNV species, RGNNV. Therefore, the development of strategies to protect different fish species against different viruses is a key issue for the aquaculture industry. In this regard, there are numerous studies focused on the use of probiotics, although their antiviral activity has been poorly investigated. Shewanella putrefaciens Pdp11, SpPdp11, is a probiotic with proven positive effects on gilthead seabream and Senegalese sole, protecting those species against several bac-
terial pathogens; however, its antiviral activity remains to be investigated. The current study is a step forward in the use of probiotics against viral infections, evaluating the anti-RGNNV activity of sonicated-SpPdp11 extracts both, in vitro and in vivo. According to our results, SpPdp11 extracts compromised RGNNV multiplication in E11 cells, affecting viral assembly and/or exit rather than genome replication. Furthermore, this antiviral activity may be produced by the capacity of the SpPdp11-extract to induce an immune response in treated cells. This antiRGNNV activity has been confirmed in vivo, since 82% of fish fed with the SpPdp11-supplemented diet survived an experimental-RGNNV infection, whereas the survival rate of fish fed with the control diet was 64%. These results suggest that SpPdp11-supplemented feeding can be a promising prophylactic tool against RGNNV and
encourage further research on other fish species and viral pathogens.
