2008/750 AGD vaccine phase III: Sea-based trials, vaccine refinement and commercialisation
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2008/750 AGD vaccine phase III: Sea-based trials, vaccine refinement and commercialisation

By Mathew Cook

In Tasmania, amoebic gill disease (AGD) is the main health concern that affects the salmon mariculture industry. It is also a major production cost (>$30m) in terms of treatment and subsequent lost production. Outbreaks of AGD are most prevalent during the spring/summer associated with high salinity and high water temperature, but are becoming a year-round problem in Tasmania. Currently, freshwater bathing is the only effective treatment for AGD. However, this is labour intensive, time-consuming, stressful to fish and costly. Given increased demand for freshwater and the high costs associated with freshwater bathing, it is not viewed as a sustainable treatment option in the long-term. The main objective of this project was to undertake sea based trials of the experimental DNA based vaccine developed for amoebic gill disease (AGD). Concurrently to this, efforts were made to try and increase the vaccines efficiency utilizing a laboratory based challenge system.

In moving to the sea, the more commercially relevant measurement of 'gill score' was used to assess vaccine efficiency. However, the results obtained both in the laboratory and in the sea up to year three of the project indicated that while the vaccine was able to significantly reduce morbidity it had little to no effect on gill score and therefore was not a commercially viable treatment option for AGD. Therefore the project developed a recombinant antigen representative of a Neoparamoeba perurans attachment protein which is now the focus of a mucosal based vaccination strategy.

This project demonstrated that the development of a reliable challenge model for AGD is critical to underpin any future AGD research. Similarly, there is a critical need for a virulent culture of N. perurans to be made available to the wider AGD research community. Vaccination against AGD is a possibility. However, the vaccine developed herein is not efficacious enough to be considered a commercial viability. The project has provided data and developed specific protocols for trialing vaccines against AGD both in the laboratory and field situations. It is also clear from the results of this project that more fundamental research into the host-pathogen interaction in AGD is required before alternatives to freshwater bathing can be considered. There is also a need for a more efficient and efficacious challenge system to support ongoing research and development of alternative treatments for AGD.