Nanostructured recombinant protein particles raise specific antibodies against the nodavirus NNV coat protein in sole.

Nervous necrosis virus (NNV) reassortant strains RGNNV/SJNNV have emerged as a potent threat to the Mediterranean marine aquaculture industry, causing viral encephalopathy and retinopathy (VER) in Senegalese sole (Solea senegalensis). In this study, a cheap and practical vaccine strategy using bacterial inclusion bodies made of the coat protein of a virulent reassortant strain of this betanodavirus was devised. The nanostructured recombinant protein nanoparticles, VNNV-CNP, were administered without adjuvant to two groups of juvenile sole, one by intraperitoneal injection and the other by oral intubation. Specific antibodies were raised in vivo against the NNV coat protein via both routes, with a substantial specific antibody expansion in the injected group 30 days post homologous prime boost. Expression levels of five adaptive immune-related genes, cd8a, cd4, igm, igt and arg2, were also quantified in intestine, spleen and head kidney. Results showed cd4 and igm were upregulated in the head kidney of injected fish, indicating activation of an adaptive systemic response, while intubated fish exhibited a mucosal response in the intestine. Neither route showed significant differential expression of cd8a. The specific antibody response elicited in vivo and the lack of any signs of toxicity over the 6-week study period in young fish (n = 100), evidences the potential of the nanoparticle as a vaccine candidate.

Toxicity of Photobacterium damselae subsp. damselae strains isolated from new cultured marine fish.

The in vivo and in vitro toxicity of bacterial cells and their extracellular products (ECPs) from 16 strains of Photobacterium damselae subsp. damselae isolated from 7 epizootic outbreaks were evaluated. On the basis of their 50% lethal dose (LD50) values (about 1 x 10(50 CFU), these strains may be considered as moderately virulent. However, their ECPs were strongly lethal for redbanded seabream Pagrus auriga causing fish death within 2 h post-inoculation (protein concentration ranged between 2.1 and 6.41 microg g(-1) fish). The bacterial ECPs tested exhibited several enzymatic activities, such as amylase, lipase, phospholipase, alkaline phosphatase, esterase-lipase, acid phosphatase, and beta-glucosaminidase. These ECPs displayed a strong cytotoxic effect on 4 fish and 2 mammalian cell lines, although this activity disappeared when ECPs were heated at 100 degrees C. The virulence of the strains tested could not be related to the hemolytic activity or to the production of the toxin damselysin. Therefore, another unknown type of toxin could play an important role in the virulence mechanisms of this bacterial pathogen.