Publication Abstract

 

Investigations of terrestrial systems have concluded that human intervention underpins in disease emergence in many ecosystems. The evidence suggests that this is also true for disease emergence in aquatic systems. High stocking density and biomass found in intensive systems favour the selection of virulent strains. The development of aquaculture has relied on the long distance transport of animals, providing pathways for diseases to extend their geographic range. Aquaculture has been an important driver for the movement of species outside their original geographic ranges (e.g. rainbow trout and Atlantic salmon are farmed across the globe). The introduction of non-native species, with their endemic pathogens and parasites, provides the conditions for potential pathogens to jump the species barrier, and thus the emergence of pathogens in new hosts. A causal web is used to elucidate the synergies that may exist between drivers for emergence.

 

Climate change is influencing disease emergence (especially vector borne diseases) in humans and terrestrial livestock. In the marine environment, disease emergence has been associated with increased water temperatures. Freshwater ecosystems have been less well studied. A risk framework has been developed that assesses the main factors influencing disease emergence in freshwater fish. The model has been used to identify pathogens whose threat to UK freshwater fish species is likely to increase as water temperatures rise (e.g. Lactococcus garvieae and Aphanomyces invadans). Biosecurity and contingency plans need to be periodically reviewed as the disease threat changes with increasing water temperature. The impact of climate change, especially when mediated through an increase in extreme weather events, will not be spatially homogenous. Geo-referenced climate data should be used to identify areas of high risk for disease emergence, where surveillance and mitigation measures can be focused 

 

Electronic sources of information on disease emergence in aquatic animals have been monitored since 2002. A total of 210 events have been recorded, almost two thirds of which were due to occurrence in a new location. A majority of these records were non-contiguous expansion which implies anthropogenic involvement. Sixty percent of all the events occurred in farmed population. Further analysis of these data are needed to examine whether disease emergence wild populations could be attributed to activities associated with aquaculture, and potential associations, in time and space, for disease emergence and the expansion of aquaculture.

 

Diseases will continue to emerge as aquaculture grows. Often only a narrow window exists for diseases to be controlled before they become widespread Better understanding drivers for disease emergence will help identify strategies to reduce the likelihood of emergence and surveillance and contingency plans for early detection and effective response.