Oral AMPs increase vaccination potential against nodavirus in European sea bass

Introduction

Nervous Necrosis Virus (NNV) is a neurotropic pathogen characterized by its ease of dispersal and high stability in the aquatic environment, increasing its dispersion, host range and impact on wild and cultured fish species. Currently, there are few commercial antiviral treatments and the development of effective, accessible, and affordable preventive or therapeutic treatments is of great importance. Among the promising candidates are antimicrobial peptides (AMPs), which can both act as direct microbials and promote the immune response. Recent studies have demonstrated that administration of AMP increases resistance to NNV challenges, likely regulating inflammation and the antibody response. However, their oral administration should be further investigated.

Methodology

Bacteria producing recombinant AMPs (dicentracin, Dic; hepcidin, Hamp; or fused NKlysin–hepcidin–dicentracin–Defensin, NHDB) and the NNV vaccine were produced, confirmed and inactivated. European sea bass (Dicentrarchus labrax) juveniles were fed with diets supplemented with recombinant AMPs alone or combined with the NNV vaccine and then challenged with NNV by bath. Survival was monitored over 30 days. Viral replication and specific antibody levels were determined.

Results

Our results show that the oral AMPs alone had a low protection capacity upon infection. However, they were able to increase protection in vaccinated fish to a significant extent, particularly the NHDB-fused AMPs. Viral replication and antibody levels were also regulated.

Conclusions

Our preliminary study indicates that oral application of AMPs during oral vaccination might be a valuable way to protect European sea bass against NNV infections.