Towards the development of a vaccine for proliferative kidney disease

This proposal will study an important disease that affects the rainbow trout aquaculture industry, proliferative kidney disease (PKD), with the objective of making significant progress towards the development of a vaccine. The disease is caused by a microscopic parasite known as a myxozoan, which causes a severe immune response in fish characterized by a chronic kidney pathology. Our recent work led to the discovery that colonial freshwater invertebrates known as bryozoans act as a reservoir of parasites infective to fish. Recently we have found that increasing temperatures cause the parasite to proliferate in bryozoans with greater numbers of released spores, suggesting that that the disease is likely to become more problematic in farmed and wild salmonid stocks as water temperatures increase due to climate change. There is already evidence for this effect in wild brown trout populations in Switzerland and wild Atlantic salmon populations in Norway and we are aware that PKD has increased in severity over the past few years in trout farms in Southern England. Currently, there are no current treatments to prevent or control the disease. However, an important characteristic of PKD is that fish that do survive an initial infection with the parasite are resistance to a subsequent exposure, and thus priming of the immune system with a vaccine is expected to be one way to control this disease. The key is to find an appropriate molecule that can trigger a protective immune response. In recent studies we have identified a number of PKD molecules, several of which have characteristics in common with molecules that elicit protection in other host-pathogen models. So in this proposal we will study the effectiveness of these molecules. We will use a recent advance in vaccine technology, and use for the most part DNA vaccines rather than protein based vaccines, since the former are a cost-effective way to screen our vaccine candidates and have been shown previously to work well in fish. Fish will be vaccinated at a commercial rainbow trout farm, that suffers from this disease every year, and the results will be assessed in terms of survival and the immune response elicited. However, we will not assume that the best vaccine candidates will be amongst the genes we have already sequenced, and so will take an alternative approach as well. The second approach will use pathogen material isolated from the fish host, as well as an intermediate host, and using molecular biology techniques we will create 'gene libraries' from this material that will contain many of the genes that can be expressed by this pathogen. In the same way as above, we will use a DNA vaccine approach to screen these gene libraries for vaccine candidates, but in this case will use 'pools' of many genes. Fish vaccinated with these different 'pools' will be assessed for disease resistance as above, and batches that show beneficial affects will be subdivided and retested, to eventually give small numbers of potential candidate molecules to look at in more detail. Since pathogen strain variation can affect the molecular composition of molecules, we will undertake a survey of some of the candidate genes from the initial approach and see if they are invariant and suitable for all strains, or whether they vary and that an eventual vaccine would require to be derived from multiple sources. In this manner, we will take a systematic approach to vaccine development for this disease, based on our past success in discovering parasite genes, and our existing expertise in molecular biology, PKD biology and fish vaccination.