Previous attempts to develop vaccines against salmon lice infection in salmon have not produced satisfactory results. Candidate antigens are difficult to identify and test for their ability to induce efficacious immune responses. Several studies have used a concealed antigen strategy, and while results initially were promising, results have been difficult to reproduce. Insufficient were also attempts to modulate the immune response of the host by applying immunoprophylactic principles against infection, among others by using DNAprime/protein boosts. For this reason, the hypothesis that the lack of protection could be related to amount of antigen used for immunisation/ low corresponding antibody responses was investigated in the Slimy project. Lice antigens were prepared from sea lice and used for the immunisation of salmon at a high antigen load.
To establish a protocol for vaccination combined with skin microbiome engineering that increases the resistance towards lice infection in Atlantic salmon. Main objectives of the project were therefore to identify protective antigens in lice preparations for their subsequent use in recombinant antigen design and vaccine delivery in a “reverse vaccinology” approach; to characterise, quantify and detail the impact of sea lice infection on the skin microbiome in Atlantic salmon in terms of its taxon presence/absence and relative abundance; and to test these prophylactic interventions at laboratory scale and in small scale field studies. Additionally, the physiological outfit of metabolites and proteins related to lice-triggered processes of the innate and adaptive immune system in salmon was intended to be studied in differently treated fish.
FHF funded project; 2019 – 2023
The new vaccination approach was successful, leading to a 65% reduction in sea lice numbers (as compared to controls) at a heavy infection load. In detail, the use of vaccines that are based on whole-louse antigens lead to reduced lice infestation rates of salmon in small-scale studies. Vaccines based on recombinant proteins of salmon lice in lipidic formulation provided a comparably good protection against lice infestation. There was a negative correlation between the level of protective antibodies in the blood circulation of the fish and the degree of infestation as high antibody levels results in decreased lice numbers. The conditioning of salmon with probiotic microbiota before an exposure experiment with lice copepodes resulted in reduced lice infestation rates. The metabolome and proteome studies are ongoing.