Chile: new vaccine reduces lice infestation by up to 53%

Advances in understanding the genome of the sea louse Caligus rogercresseyi have broadened the search for targets to develop vaccines capable of reducing the number of the parasites on farmed salmon. Among the candidates studied, peritrophins and cathepsins stand out, reports Fish Farming Expert's Chilean sister site, Salmonexpert.cl.

While a cathepsin-based vaccine achieved reductions in parasite load of 44% in early stages and 57% in adult parasites, in addition to causing morphological alterations in lice, a formulation directed against peritrophin achieved a reduction of close to 12%.

Based on this, the same scientists who were behind this discovery and also the well-known Ipath iron chelating vaccine, are looking to identify other components of the parasite that may generate more consistent protection.

In a study published by researchers from the Incar2 Centre and the Biotechnology Center of the University of Concepción, a new experimental vaccine based on two functional domains of the vitellogenin (Vtg) of C. rogercresseyi was evaluated.

New approach to Caligus control

The researchers focused their attention on Vtg, a protein present in C. rogercresseyi, from which, through in silico analysis, they identified two functional domains associated with the von Willebrand factor (VWF), called CrVtg-VWF1 and CrVtg-VWF2, which presented promising characteristics as vaccine candidates.

Both domains were produced as recombinant proteins and used separately in experimental formulations.

To assess its protective capacity, experts immunised 180 Atlantic salmon. After 400 degree days since vaccination, the fish were challenged with 35 copepods per individual and subsequently evaluated at seven and 21 days post-infestation.

Better as time went on

Initial results showed a reduction of approximately 12% in the fixation of chalimus I-stage lice at seven days in the vaccinated groups.

But the difference became much more evident later. At 21 days, the vaccine based on CrVtg-VWF1 reached a relative efficacy of 40.2%, while the formulation with CrVtg-VWF2 reached 53.4% compared to the control group.

“The CrVtg-VWF vaccines based on the functional domains of C. rogercresseyi vitellogenins demonstrated efficacy in reducing the parasitic load of sea lice, with 40.2% for CrVtg-VWF1 (Vac A) and 53.4% for CrVtg-VWF2 (Vac B), affecting both male and female parasites, and showed improved performance compared to vaccines targeting full-length vitellogenin proteins,” the authors explained.

Based on their results, the scientists concluded that VWF domain-based vaccines offer a "new approach to controlling sea lice infestations in Atlantic salmon".

Read the abstract of the study titled “Protective and immunostimulatory effects of a vitellogenin functional domain-based vaccine in Atlantic salmon against Caligus rogercresseyi ”, here.