Atlantic salmon are continuously face multiple pathogens throughout the production cycle, such as the sea louse Caligus rogercresseyi and the intracellular bacterium Piscirickettsia salmonis. These coinfections can compromise the effectiveness of commercial vaccines, reducing the host’s ability to resist infection. Nevertheless, the multipathogen infections impact on the transcriptome of vaccinated fish remains unexplored. This study aimed to evaluate the transcriptome responses of vaccinated Atlantic salmon during sequential infections with C. rogercresseyi and P. salmonis. Additionally, we assessed the vaccine’s capacity to elicit cross-protective immunity against both pathogens.
Atlantic salmon were immunized with a commercial pentavalent vaccine (P), a commercial live attenuated bacterial vaccine (A), and our recombinant Ipath vaccine. Four experimental groups were immunized: Ipath, P+A, P+A+Ipath, and PBS as a control. Following 400 UTAs, vaccinated salmons were infested with 35 copepodids per fish. Sea lice attachment was evaluated 25 days post-infestation (dpi). Following two weeks, salmon were infected with P. salmonis 1E8. The mortality was recorded daily. Also, head kidney tissue samples were collected for mRNA Illumina sequencing at 25 dpi for sea lice-dpi and 16 dpi for P. salmonis infections. Vaccination strategies that included Ipath showed higher reduction in sea lice burden, with 73.7 and 69.8 % in the groups Ipath and P+A+Ipath, respectively. Furthermore, the Ipath vaccinated group showed a delate in salmon death after the P. salmonis infection compared with the other experimental groups. Throughout sea lice infection P+A+Ipath group upregulated key immune-related genes, such as cathelicidin, major histocompatibility complex class-I, and interferon regulatory factor, suggesting an innate and adaptive response. Moreover, during P.salmonis infection the P+A group showed a marked gene downregulation compared to the respective controls, including immune transcripts such as metalloendopeptidase, interferon regulatory factor 7 and T-lymphocyte surface antigen Ly-9-like. Biological processes and pathways related to response to stress were highly enriched in the P+A group. Notably, Ipath and P+A+Ipath groups triggered the regulation of genes associated with iron balance, such as ferric chelate reductase 1, when challenged with both pathogens. This study reveals a vaccine-dependent transcriptomic patterns. Also, a synergy between Ipath and commercial vaccines, especially at the level of iron modulation and immune response, offering a new strategy for integrated C. rogercresseyi and P. salmonis control in salmon farming.
Acknowledgments: This study was funded by FONDECYT #3240484, FONDECYT #1210852 and FONDAP #15110027.