Assessing the risk of an emerging salmonid disease

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Proliferative kidney disease (PKD) is an emerging disease of salmonid fish that is increasing in severity and geographic range. PKD is caused by the myxozoan Tetracapsuloides bryosalmonae (Tb) and can effect significant and sometimes catastrophic mortality in farmed and wild fish populations. PKD is believed to have contributed to declines in brown trout populations in Swiss rivers and recent outbreaks in wild fish populations in Iceland and Norway have increased the geographic range of the disease. All salmonids are susceptible and outbreaks and declines have been linked with increasing water temperatures and nutrient levels. Tb exploits highly clonal bryozoans as primary hosts and spores released into the water are infective to fish. The aim of this project is to assess the risk of PKD for wild fish populations in the UK by focusing on the disease source. Our objectives are thus to: 1) Characterise bryozoan population dynamics and the dynamics of Tb within this host. 2) Establish risk factors associated with Tb prevalence and burden in bryozoans and subsequent transmission to fish hosts. 3) Use risk models developed from epidemiological and field studies (conducted in Objective 1) to produce and validate a protocol to sample bryozoans as a surrogate for sampling wild fish in order to assess and monitor parasite levels and to produce a risk map for PKD in wild fish CASE Project Partners at the Environment Agency (EA) and Centre for Fisheries & Aquaculture Science (Cefas) will spearhead the development of statistical modelling to identify risk factors for PKD, to develop a standard operating procedure for monitoring PKD risk, and to produce a risk map. Academic supervisors will supervise the requisite epidemiological studies that will enable risk factor analysis. As a result the project will generate practical outputs of benefit to regulatory agencies (see below) and will significantly contribute to fundamental knowledge of the evolutionary ecology of hosts and parasites by characterising the interactions of colonial hosts and endoparasites in the wild and the potential effect of environmental variation on these interactions. The student would gain training in a range of transferable and technical skills and would interact broadly during research with CASE partners, fish farm partners and academic institutes. Drivers for the work How environmental conditions promote the development of PKD is poorly understood but such understanding is crucial for identifying risk factors associated with disease outbreaks and the susceptibility of wild fish populations. Due to the value of salmonid fish and the many pressures facing brown trout populations, monitoring fish health in the wild remains a serious challenge. Using bryozoans as a surrogate for monitoring PKD would provide a valuable and novel approach for managing wild fish populations, affording a basis for national monitoring and minimising future disease impacts.