No abstract

Infection with parasitic copepod salmon louse Lepeophtheirus salmonis, represents one of the most important limitations to sustainable Atlantic salmon (Salmo salar L.) farming today in the North Atlantic region. The parasite exerts negative impact on health, growth and welfare of farmed fish as well as impact on wild salmonid populations. It is therefore central to ensure continuous low level of salmon lice with the least possible handling of the salmon and drug use. To address this, vaccination is a cost-effective and environmentally friendly control approach. In this study, efficacy of a vaccine candidate, containing a peptide derived from ribosomal protein P0, was validated post infestation with L. salmonis, at the lab-scale. The sampling results showed good potential of the vaccine candidate when administered intraperitoneally in the host, in reducing the ectoparasite load, through reduction of adult female lice counts and fecundity and with greater presumptive effect in F1 lice generation. The sampling results correlated well with the differential modulation of pro-inflammatory, Th1, Th2 and T regulatory mediators at the transcript level at different lice stages. Overall, the results supports approximately 56% efficacy when administered by intraperitoneal injection. However, additional validation is necessary under large-scale laboratory trial for further application under field conditions.

Title): Effectiveness of fusion peptide-based vaccine TT-P0 on the dynamics of salmon lice 2 (Lepeophtheirus salmonis) infection in Atlantic salmon (Salmo salar L.) 3 4 (Short title): TT-P0 vaccine and salmon lice infection 5 6 (Authors): Abstract 24 Infection with parasitic copepod salmon louse Lepeophtheirus salmonis, represents one of the most 25 important limitations to sustainable Atlantic salmon (Salmo salar L.) farming today in the North 26 Atlantic region. The parasite exerts negative impact on health, growth and welfare of farmed fish as 27 well as impact on wild salmonid populations. It is therefore central to ensure continuous low level 28 of salmon lice with the least possible handling of the salmon and drug use. This necessitates 29 development of an alternative preventive strategy that can document both effect on lice and that 30 fish welfare is maintained in a satisfactory manner with high economic impact. To address this, 31 vaccination is a cost-effective and environmentally free control approach avoiding the 32 disadvantages of chemical and mechanical treatments. In this study, efficacy of a vaccine candidate 33 (TT-P0), encompassing a peptide derived from ribosomal protein P0 and promiscuous T cell epitopes 34 from tetanus toxin and measles virus, was validated post infestation with L. salmonis, at the lab-35 scale. The sampling results showed good potential of the TT-P0 vaccine in limiting the ectoparasite 36 load, when administered intraperitoneal in the host, by affecting the total adult lice female counts 37 and fecundity, with greater presumptive effect in F1 lice generation. This consequently speculate 38 vaccine's potential to reduce the amount and frequency of chemical drug, mechanical treatment 39 and handling stress, currently used in salmon farming practices, thus improving the fish welfare, 40 environment and economy. On the other hand, the vaccine showed minimal secondary effects and 41 differential modulation of pro-inflammatory, Th1, Th2 and T regulatory mediators at the transcript 42 level with respect to different lice stages in the vaccinated groups as compared to control. Overall, 43 the results indicated potential effectiveness of TT-P0 antigen as a good and safe vaccine candidate 44 against salmon lice. This is a very important preliminary documentation of the TT-P0 vaccine, as a 45 preventive measure, for sustainable and profitable growth of the salmon industry. However, further 46 validation is necessary under field conditions. 3 47 Author summary 48Reducing the impact of salmon lice is a major concern for salmon producers around the globe. These 49 parasitic copepods feed on host mucus, skin and blood, causing a negative impact due to reduction 50 in host immune competence and making them more susceptible to other infections or by 51 transmitting pathogens to the host. Farmed salmon populations are the main reservoirs and 52 increasing numbers of salmon lice in the farms, negatively impacts' wild salmon populations. The 53 available control methods rely mainly on pestici...

The overexpression of GATA-3, T-bet and TGF-ß may theoretically induce IL-4/A, IFN-γ and IL-17A expression, respectively. Whether this also applies to fish is not yet known. The plasmid vectors encoding reporter gene (RFP)-tagged T-bet, GATA-3 and TGF-ß were used as overexpression tools, transfected into cells or injected intramuscularly to monitor the expression of IFN-γ, IL-4/13A and IL-17A. In addition, the fish were either experimentally challenged with Vibrio anguillarum (VA group) or Piscirickettsia salmonis (PS group). The reporter gene (RFP) inserted upstream of the GATA-3, T-bet and TGF-ß genes, was observed in muscle cell nuclei and in inflammatory cells after intramuscular (i.m.) injection. PS group: following the injection of GATA-3 and T-bet-encoding plasmids, the expression of GATA-3 and T-bet was high at the injection site. The spleen expression of IFN-γ, following the injection of a T-bet-encoding plasmid, was significantly higher on day 2. VA group: The T-bet and GATA-3-overexpressing fish expressed high T-bet and GATA-3 mRNA levels in the muscles and on day 4 post-challenge. The expression of TGF-ß in the muscles of fish injected with TGF-ß-encoding plasmids was significantly higher on days 7 (8 days pre-challenge) and 19 (4 days after challenge). The protective effects of the overexpression of T-bet, GATA-3 and TGF-ß on both bacterial infections were negligible.