Development of an immersion vaccine for salmonids

Fish handling and injection-based vaccination is one of the biggest causes of stress for fish and always results in increased mortality due to post-vaccination outbreaks of saprolegniosis and bacterial infections. In Scotland alone, millions of pre-smolt (10% of all hatched salmon) die due to Saprolegnia infections after receiving an injection-based vaccine. Therefore, there is an urgent need to develop better vaccination practices to increase animal welfare and reduce mortalities. Immersion vaccination of fish was the first method used to demonstrate effective protection against bacterial diseases, but was overtaken by injection vaccination due to the need for inclusion of vaccine adjuvants. Should enhanced delivery of antigens be possible by the immersion route clearly this holds enormous promise to completely obviate fish handling, thus reducing stress and significantly lowering mortality.
The central hypothesis of our programme is that immersion vaccination with recombinant SpHtp1-coupled antigens can be used successfully to protect fish against diseases.
Our overall objective is to develop and commercialise the SpHtp1 translocation mechanism into an immersion vaccine delivery method for salmonids and other farmed fish.
We have already demonstrated that our patented method can be used successfully and effectively in directing proteins into live fish. Furthermore, we have observed specific antibody production in trout that were immersed in a solution of SpHtp1 fused to mRFP.

Therefore, our main outputs will be:
1) Evidence that the translocating peptide of SpHtp1 coupled to selected antigens give protection against disease of concern in salmonid aquaculture, in immersion vaccination trial experiments.
2) Optimisation of the immune response in fish.
3) A highly efficient and productive SpHtp1-recombinant protein overexpression method for large-scale production and future commercialisation of the vaccine method by our commercial partners BAHL and Pulcea Ltd.
4) A method to recycle and inactivate the immersion vaccine that can be employed on site in the farm.

All outputs will be exploited by BAHL and Pulcea Ltd. in obtaining licenses and approvals for commercialisation and eventually full use by the aquaculture industry. Antigens of essential pathogens are already available through BAHL, and further antigens will be sought in future projects by the UoA and BAHL. The current application is ambitious but achievable and will take 24 months to complete because of the significant amount of work that is proposed.

In summary, the potential impact of an immersion vaccine for finfish is "aquaculture industry-transformational" as fish vaccinated by injection could be eliminated, which would greatly increase the welfare of the fish and minimise fish losses and thus financial losses in the aquaculture business worldwide.

Fish handling and injection-based vaccination is one of the biggest causes of stress for fish and always results in increased mortality due to post-vaccination outbreaks of saprolegniosis and bacterial infections. In Scotland alone, millions of pre-smolt (10% of all hatched salmon) die due to Saprolegnia infections after receiving an injection-based vaccine. Therefore there is an urgent need to develop better vaccination practices to increase animal welfare and reduce mortalities. Immersion vaccination of fish was the first method used to demonstrate effective protection against bacterial diseases, but was overtaken by injection vaccination due to the need for inclusion of vaccine adjuvants. Should enhanced delivery of antigens be possible by the immersion route clearly this holds enormous promise to completely obviate fish handling, thus reducing stress and significantly lowering mortality.

Therefore, the main output of this Innovation Project is to establish whether the immersion vaccination method can provide immunity to economically important pathogens of salmon. Our ultimate goal is to vaccinate fish (through immersion) only once (but maybe two vaccination rounds are needed to give best protection) with a combination of relevant antigens to provide protection against viral, bacterial and parasite diseases found in aquaculture at present. Benchmark Animal Health Ltd (BAHL) has several suitable antigens of a range of pathogens available of which we initially will test three for validation of the immersion vaccination technique following fish challenge experiments.

We will optimise the best method to produce the vaccine in large quantities and we will confirm whether we can re-use and also inactivate the vaccine (with Pulcea Ltd.) to allow approval by the various legislative bodies for use in recirculating water systems in fish farms. Following future identification of suitable antigens of parasites by BAHL and the UoA, a combined immersion vaccine could in principle incorporate any target antigens including viral, bacterial and parasites.

The potential impact of a combined immersion vaccine for finfish is "aquaculture industry-transformational" as fish vaccination by needle can be eliminated, which will greatly increase the welfare of the fish, minimise fish losses and thus financial losses in the aquaculture business worldwide.