Exploring Sea Lice Vaccines against Early Stages of Infestation in Atlantic Salmon (Salmo salar)

Abstract

The sea louse Caligus rogercresseyi genome has opened the opportunity to apply the reverse vaccinology strategy for identifying antigens with potential effects on lice development and its application in sea lice control. This study aimed to explore the efficacy of three sea lice vaccines against the early stage of infestation, assessing the transcriptome modulation of immunized Atlantic salmon. Therein, three experimental groups of Salmo salar (Atlantic salmon) were vaccinated with the recombinant proteins: Peritrophin (prototype A), Cathepsin (prototype B), and the mix of them (prototype C), respectively. Sea lice infestation was evaluated during chalimus I-II, the early-infective stages attached at 7-days post infestation. In parallel, head kidney and skin tissue samples were taken for mRNA Illumina sequencing. Relative expression analyses of genes were conducted to identify immune responses, iron transport, and stress responses associated with the tested vaccines during the early stages of sea lice infection. The vaccine prototypes A, B, and C reduced the parasite burden by 24, 44, and 52% compared with the control group. In addition, the RNA-Seq analysis exhibited a prototype-dependent transcriptome modulation. The high expression differences were observed in genes associated with metal ion binding, molecular processes, and energy production. The findings suggest a balance between the host’s inflammatory response and metabolic process in vaccinated fish, increasing their transcriptional activity, which can alter the early host–parasite interactions. This study uncovers molecular responses produced by three vaccine prototypes at the early stages of infestation, providing new knowledge for sea lice control in the salmon aquaculture.

Comparative Transcriptomics in Atlantic Salmon Head Kidney and SHK-1 Cell Line Exposed to the Sea Louse Cr-Cathepsin

“…First, the recombinant protein Cr-cathepsin associated with the secretome of the sea louse [ 12 ] was expressed and purified ( Figure S1 ). The cell viability on the SHK-1 cell line exposed to recombinant Cr-cathepsin was determined.…”

“…Developing successful vaccines for commercial application against sea lice in salmon farming production is time-consuming and expensive. Several potential vaccine candidates against sea lice have been reported [ 10 , 11 , 12 , 13 , 14 , 40 , 41 , 42 ]. Hence, parasite transcriptomic studies have provided valuable information for understanding the molecular mechanisms involved in the host-parasite interaction [ 43 , 44 ].…”

“…For the present study, a cathepsin-encoding mRNA sequence previously identified and characterized by our work group was selected as a recombinant test antigen [ 12 ]. Briefly, the nucleotide sequence was chemically synthesized with codon optimization based on E. coli codon preferences, and was subsequently cloned into a pET30a expression vector (GenScript, Piscataway, NJ, USA).…”

“…Atlantic salmon is the primary salmon species in farming worldwide [ 4 ], and many vaccine formulations have been proposed to control infectious diseases that affect it. For instance, vaccines have been developed for Vibrio anguillarum [ 5 ], Yersinia ruckeri [ 6 ], salmonid alphavirus (SAV) [ 7 ], Moritella viscosa [ 8 ], infectious pancreatic necrosis virus (IPNV), infectious salmon anemia virus (ISAV) [ 9 ], Lepeoptheirus salmonis [ 10 , 11 ], and C. rogercresseyi [ 12 , 13 , 14 ]. Most candidate vaccines are developed with an attenuated or killed microorganism component or a particular surface protein or toxin.…”

“…The transcriptomic response of Atlantic salmons immunized with the prototypes was mainly related to the modulation of metabolic processes, energy production, and metal ion handling, which has been essential for the host response to the early C. rogercresseyi stages. Furthermore, the group vaccinated with the cathepsin antigen showed a significant parasite burden reduction, making it a promising vaccine candidate [ 12 , 35 ]. Despite these results, the sea lice vaccine development bottleneck is in vivo testing, because it is necessary to use a large amount of fish to evaluate several recombinant protein candidates, dosage, and polyvalent formulation strategies.…”