Protective and immunostimulatory effects of a vitellogenin functional domain-based vaccine in Atlantic salmon against Caligus rogercresseyi.

Sea lice cause economic losses in global salmon aquaculture, and the treatments used, mainly delousing drugs, have become less effective. Thus, moving forward, developing new, sustainable control strategies is required. In this context, our study evaluated the use of a recombinant vaccine for controlling sea lice. The von Willebrand factor domains (VWF) from two Caligus rogercresseyi vitellogenins (CrVtg), CrVtg-VWF1 and CrVtg-VWF2, were selected for immunization and challenge in Atlantic salmon. In silico analyses confirmed the immunogenic potential of these domains. The recombinant protein domains were incorporated into experimental vaccine formulations, separately. A total of 180 Atlantic salmon were immunized and subsequently challenged with 35 copepodids per fish after 400 degree-days post-vaccination. At 7- and 21 days post-infestation (dpi), vaccine efficacy was evaluated based on parasite load quantification. Moreover, the expression of immune-related genes was evaluated in fish skin and head kidney tissues. At 7 dpi, chalimus I attachment was reduced by approximately 12% in the vaccinated groups, in the case of adults, 21 dpi, the efficacy was 40.2% for CrVtg-VWF1 and 53.4% for CrVtg-VWF2, relative to the control group. Moreover, CrVtg-VWF antigens primarily stimulated significant upregulation of MHC II, IgM, and IgT transcripts in the head kidney tissue compared with the control group. These results demonstrate the potential of VWF domain-based vaccines as a novel approach for controlling sea lice infestations in Atlantic salmon.