Synergistic Protection of Atlantic Salmon Against Caligus Rogercresseyi and Piscirickettsia Salmonis Using IPath® and...

Vaccine-based approaches provide a sustainable method for controlling pathogens in aquaculture. Our team previously created the IPath® vaccine, a recombinant formulation with metal-chelating properties. This study aimed to evaluate the performance of IPath® in salmon vaccinated with the mandatory vaccines used commercially in Chile, and to assess their effects on the transcriptome profiles of Atlantic salmon challenged with Caligus rogercresseyi and co-infected with Piscirickettsia salmonis. Four experimental groups of Atlantic salmon were immunized: IPath®, BlueGuard® (B) + Alpha Ject LiVac® SRS® (L), B + L + IPath®, and PBS as a control. After accumulating 400 thermal units (ATUs), vaccinated salmon were exposed to a coinfection model involving 35 copepodids per fish for 25 days, followed by an intraperitoneal infection with P. salmonis (1 × 10^8) for 16 days, with mortality recorded daily. Head kidney tissue samples were collected for mRNA Illumina sequencing at 25 days post-infection (dpi) for sea lice and at 16 dpi for P. salmonis infections. IPath® and B + L + IPath® showed 73.7 and 69.8% reduction in sea lice burden, respectively. Furthermore, the IPath® vaccinated group showed a delay in salmon mortality following P. salmonis infection compared with the other experimental groups. During sea lice infection, the B + L + IPath® group upregulated key immune-related genes, such as cathelicidin, major histocompatibility complex class I, and interferon regulatory factor, indicating an innate and adaptive immune response. During P. salmonis co-infection, the B + L group downregulated immune-related transcripts, including metalloendopeptidase, interferon regulatory factor 7, and T-lymphocyte surface antigen Ly-9-like. Biological processes and pathways related to stress response were highly enriched in the B + L group. Notably, the IPath® and B + L + IPath® groups triggered gene regulation associated with iron balance, such as ferric chelate reductase 1, in response to both pathogens. A synergy between IPath® and commercial vaccines, especially in iron regulation and immune response, offers a new approach for integrated control of C. rogercresseyi and P. salmonis in salmon farming.