The application of risk and disease modelling to emerging freshwater diseases in wild aquatic animals

Abstract

Summary 1. Emerging diseases pose significant ecological and economic threats in fresh waters. Both risk assessment and mathematical modelling have potential to improve our understanding of the uncertainties associated with emerging disease events and make informed predictions about their likely impact. 2. We review the different methodologies that may be used to estimate the likely geographic spread and potential impact of new and emerging diseases in fresh waters. We also highlight the limitations of the currently available methods and requirements for future development. 3. In the realm of aquatic animal health, risk assessment has been used mainly to examine the risks of disease spread through international trade import risk analysis (IRA). Import risk analysis of newly emerged diseases underpins the development of appropriate risk mitigation measures to minimise further spread. This is best illustrated by assessments of the spread of Gyrodactylus salaris and also illustrates how risk assessment can examine disease interaction between wild and farmed fish. 4. Various approaches have been employed to study disease transmission within freshwater fish populations at a range of spatial scales. There is scope for the application of these techniques to predict the impact of economically and environmentally important emerging freshwater diseases that arise from new pathogens, known diseases spreading to new locations or changes in pathogenicity owing to changing environmental conditions (e.g. because of climate change). 5. Population models are widely used in freshwater fishery management. The integration of disease processes within freshwater aquatic animal population models is required to provide tools to assess the likely impact of newly emerged diseases and allow mitigation measures to be assessed. 6. Compared with their use in other areas of animal health, modelling has been relatively little used for aquatic animal disease studies. The wide range of modelling methods used to study disease in human and terrestrial animals can usefully be applied to inform the development of policies to protect the health of wild stocks from emerging diseases.

Assessing the population transmission dynamics of tilapia lake virus in farmed tilapia

“…In aquaculture systems, confinement stress such as high densities of rearing fishes is more likely to weaken the immune systems, resulting in vulnerability to pathogen infections (Portz, Woodley, & Cech, ). Thrush, Murray, Brun, Wallace, and Peeler () also revealed that high host density, poor environment and intercurrent disease (occurring during the course of another disease) undermined immunity in farmed stocks and reduced resistance to diseases while enhancing contact frequencies.…”

Disease emergence and invasions

“…In practice, it may be more realistic to aim for mitigation and management of EIDs and invasions guided by robust risk assessment on a case‐by‐case basis (Thrush et al . ). We thus encourage those engaged in EID and invasion research to facilitate this with further cross‐fostering of ideas and approaches.…”

“…Tatem, Hay & Rogers ; see also Thrush et al . for risk assessment models applied to aquatic EIDs). Some papers recognize structural similarities between invasions and emergence; for instance, Chades et al .…”

Design and implementation of a collaborative epidemiological surveillance system for aquaculture (VECA)

“…Also, recently it has shown the potential of surveillance systems based on risk for early detection of emerging diseases in aquaculture through the development of epidemiological models (Thrush et al . ).…”