DEVELOPMENT OF A MUCOSAL ADJUVANT FOR FISH VACCINATION

Aquaculture is one of the fastest growing sectors that provide food to the expanding world population. Already ~50% of fish consumed by humans worldwide is produced in aquaculture, and this figure is projected to rise further. Like other food producing sectors, the sustainability of the aquaculture industry relies on good management of fish health and effective control of diseases. Outbreaks of infectious diseases can lead to heavy economic losses which may require many years to recover. During the last 30 years, vaccination has become an important means to improve fish resistance to bacteria, and has allowed a significant reduction in the use of antibiotics and toxic chemicals in fish farming, with tremendous benefits in terms of the environmental impact of the industry as well as improved fish health. The most effective way to achieve protection against diseases is to administer vaccines via intraperitoneal injection, partly due to the fact that antigens can be slowly released with the addition of oil based adjuvants for activation of the immune system. Despite the superior protection, this method causes stress to the fish, is labour intensive and can induce unwanted side-effects such as peritoneal adhesions, granulomas and even autoimmunity. However, immersion vaccination, where the fish are simply placed into a solution of diluted vaccine, has been shown to work in fish but to date is limited to a couple of bacterial pathogens and typically requires boosters for full protection, limiting its use. The need for effective adjuvants has largely driven injection vaccination, and this needs to be revisited with the appearance of several highly efficacious mucosal adjuvants being developed for use in mammals/humans. By linking a world leading mucosal adjuvant group at Oxford and a world leading fish immunology group at Aberdeen, this proposal plans to optimise the use of a novel mucosal adjuvant for use in fish, that has been developed by Professor Sattentau. Initially we will prepare stable formulations containing a killed bacterial pathogen (Yersinia ruckeri), that are suitable for testing in fish. We will use three formulations that vary in terms of the amount of adjuvant being used, and will compare the responses elicited in the fish (rainbow trout) with those elicited by a commercial immersion vaccine to this disease. We will examine the ability to enhance the expression of a number of important immune genes, thought to be involved in protective responses, as well as blood antibody levels. We will select the best formulation in terms of the responses elicited, to be used in a further experiment where the fish will be vaccinated and then exposed to the live pathogen, to see if the responses give good protection/immunity. If successful the results would have the potential to revolutionise immersion vaccination of fish. Enhanced immune responses/protection obtained with effective mucosal adjuvants may avoid the need for booster vaccination following immersion vaccination, or allow protective responses to be induced to diseases that currently require adjuvanted IP injection vaccination. We believe such an approach has the capacity for a step change in immersion (mucosal) vaccination technology for fish.