Optimalisering: Development of salmon lice viral vectors as a tool to regulate sea lice biology

Salmon lice are parasites that lead to large costs in the salmon farming industry. Calculations show that about 10% of the salmon production cost is tied directly to salmon lice treatment. In addition, there are large indirect expenses such as expenses in connection with lice surveying, and fines incurred if the number of lice is too high. There have also been several cases where the slaughtering of total fish stock has been ordered due to high lice counts. A history of low numbers of salmon lice is also necessary for companies wishing to expand operations. In addition to the direct economic cost for the salmon farmers, concerns have been raised that the salmon lice, as a result of commercial fish farming, play a role in the observed decline in wild salmon and sea trout stocks. Salmon lice are combated by the use of pharmaceuticals in addition to the use of cleaner fish. The first method is becoming increasingly less effective as salmon lice has developed multiple resistance against the chemicals used. Biocontrol by the use of cleaner fish also represent a danger of introducing other fish pathogens into the salmon cages, as well as depleting natural population of cleaner fish. The researchers responsible for this project proposal have described the first known viruses found naturally in the salmon louse. Uniquely, in this project the genomes of these recently identified viruses were manipulated in an effort to make gene transfer vehicles. The resulting modified viruses were to be used to further the study of sea lice biology and to improve salmon lice management strategies. Since there are no available cell lines from salmon lice, the work commenced by finding compatible cell lines and from there on to assemble all the components necessary for the production of modified salmon lice viruses. However, since one of the essential components in the system turned out to be toxic both in insect and fish cells there is still work to be done with testing of components from more viruses or by changing the toxic component before modified salmon lice viruses can be produced.

Two more salmon lice viruses have been characterized by the Fish Disease Research Group since the initiation of this project, and the techniques developed at the start of this project allowed for rapid genome termini determination for these viruses. The project lead to the discovery that expression of the L protein from the salmon lice viruses appears to be toxic to both insect and fish cells. Future studies would be required to determine the mechanism behind the apparent toxicity and whether the protein can be adapted to allow for its function in a non-toxic manner when overexpressed in cell culture. The project has paved the way for further study of these viruses and the establishment of a reverse genetics system for salmon lice viruses.

Salmon sea lice (L. salmonis) represent a socioeconomic burden and to date no effective or environmentally friendly cure is available. They are able to infect both wild and farmed Salmon in the Atlantic or Pacific Oceans. At present several international pharmaceutical companies have undertaken the challenge to control sea lice including Pharmaq, Novartis, and MSD. A current and common strategy employed by these companies is the use of chemical treatments of farmed salmon and vaccine development. These strategies are expensive and not effective and can account for at least 10% of the cost of salmon and has a 1.5BNOK market value. The research team described here has identified and characterized novel viruses that are able to infect sea lice and related viruses that are possibly present in all members of the Caligidae. Uniquely, this project will manipulate the genome of these recently identified viruses to make gene transfer components. The overall deliverable is to provide gene transfer vehicles to understand and regulate sea lice biology which will lead to salmon lice management. This issue has been and remains the bottleneck of the entire issue of salmon lice control, since a great deal of information and genes of interest have been compiled and are waiting for a suitable delivery system. Thus, this successful execution of this project will enable many studies and trials to combat the salmon sea lice. We envision a business model where viral vectors are developed and sold as a commercial kit.