Development of in vitro assays to determine vaccine efficacy in fish

Fish farming in the UK has increased dramatically over the last two decades, with salmonid fish the focal point of this development. Of various factors that impact on the sustainability of the industry, fish health is key with a number of disease issues of particular concern. The development of fish vaccines is at the heart of fish management but new vaccines require thorough testing before they can be marketed, and this is currently reliant upon mortality testing where fish are exposed to virulent pathogens and survival is measured. This programme will explore the potential to use an in vitro assay as a correlate of disease resistance following vaccination of fish, using two well known fish Gram negative bacterial pathogens as models, Aeromonas salmonicida the causative agent of Furunculosis and Yersinia ruckeri the causative agent of Enteric Redmouth disease. Thus this proposal aims to significantly reduce the numbers of animals suffering from lethal infection during future vaccine development. On the basis that vaccination relies on the activation of T cells to effect specific cell-mediated responses, we aim to study these cellular responses and specifically develop assays to determine the numbers of cells producing and secreting cytokines (in this case IL-17 and IL-22) associated with Th cell protective responses to extracellular bacterial pathogens. The production of these key cytokines will be studied using two tools, flow cytometry and real-time PCR, which will complement each other and give a clear picture of the magnitude and specificity of the responses elicited in trout given efficacious vaccines and then exposed to the homologous or a heterologous pathogen challenge. Although we are concentrating on bacterial diseases in trout, the data obtained would serve more generally as a proof in principle of this approach for fish. By allowing the measurement of relevant protective immune responses we believe it should be possible to undertake a great deal of vaccine optimisation without the need for lethal challenge experiments using virulent pathogens, and therefore this study will help reduce fish suffering during future vaccine development programmes.

• Further Funding: NC3Rs PhD Studentship, Development of a method for non-lethal sampling from individual fish to investigate host responses to ectoparasites, October 2014, £90,000