Identification and characterization of two salmon louse heme peroxidases and their potential as vaccine antigens.

Salmon louse, Lepeophtheirus salmonis, represents major challenge for salmon farming. Current treatments impose welfare issues and are costly, whereas prophylactic measures are unavailable. Two salmon louse heme peroxidases (LsPxtl-1 and LsPxtl-2) were tested for their importance for parasite development and as potential vaccine candidates. LsPxtl-1 possesses two heme peroxidase domains and is expressed in ovaries and gut, whereas LsPxtl-2 encodes one domain and contains N-terminal signal peptide and an Eph receptor ligand-binding domain. LsPxtl-1, but not LsPxtl-2, knockdown in nauplius II stage caused poor swimming and death, indicating its importance for parasite development. Immunizations using single DNA plasmid injection encoding the peroxidases or heterologous prime (DNA) and boost (recombinant LsPxtl-2 protein) gave non-significant reduction in lice numbers. Single injection gave low specific antibody levels compared with the prime-boost. The findings suggest LsPxtl-1 is important for parasite development but formulations and vaccination modalities used did not significantly reduce lice infestation.

Sea Lice (Lepeophtheirus salmonis) Infestation Reduces the Ability of Peripheral Blood Monocytic Cells (PBMCs) to Respond to and Control Replication of Salmonid Alphavirus in Atlantic Salmon (Salmo salar L.).

Here we have studied the impact of lice (Lepeophtheirus salmonis) infestation of donor fish on the ability of isolated peripheral blood monocytes (PMBCs) to control the replication of salmonid alphavirus (SAV) ex vivo. PMBC were collected by Percoll gradients at eight and nine weeks post copepodid infestation of Atlantic salmon post smolt. Uninfested fish were controls. PBMCs were then infected ex vivo with SAV (subtype 3), and samples were collected for analysis at two, four, and six days post virus infection. Virus titer in the supernatant was assayed in CHH-1 cells, and in addition, the relative expression of the virus structural protein E2 and selected host antiviral genes, IRF9, ISG15, Mx, and IFIT5, were assayed using real-time PCR. Significantly higher virus replication was detected in cells collected from lice-infested fish compared to controls. Higher virus titer coincided with an inability to upregulate the expression of different immune genes, IFIT5, IRF9, and Mx. These findings point towards compromised ability of PMBCs from lice-infested fish to control virus replication, and, to our knowledge, is the first report showing the direct effect of lice infestation on the interplay between viruses and immune cells. There is a possible impact on the dynamic spread of viral diseases in the aquatic environment.