The application of epidemiology in aquatic animal health -opportunities and challenges

Abstract

Over recent years the growth in aquaculture, accompanied by the emergence of new and transboundary diseases, has stimulated epidemiological studies of aquatic animal diseases. Great potential exists for both observational and theoretical approaches to investigate the processes driving emergence but, to date, compared to terrestrial systems, relatively few studies exist in aquatic animals. Research using risk methods has assessed routes of introduction of aquatic animal pathogens to facilitate safe trade (e.g. import risk analyses) and support biosecurity. Epidemiological studies of risk factors for disease in aquaculture (most notably Atlantic salmon farming) have effectively supported control measures. Methods developed for terrestrial livestock diseases (e.g. risk-based surveillance) could improve the capacity of aquatic animal surveillance systems to detect disease incursions and emergence. The study of disease in wild populations presents many challenges and the judicious use of theoretical models offers some solutions. Models, parameterised from observational studies of host pathogen interactions, have been used to extrapolate estimates of impacts on the individual to the population level. These have proved effective in estimating the likely impact of parasite infections on wild salmonid populations in Switzerland and Canada (where the importance of farmed salmon as a reservoir of infection was investigated). A lack of data is often the key constraint in the application of new approaches to surveillance and modelling. The need for epidemiological approaches to protect aquatic animal health will inevitably increase in the face of the combined challenges of climate change, increasing anthropogenic pressures, limited water sources and the growth in aquaculture.Table of contents1 Introduction 42 The development of aquatic epidemiology 73 Transboundary and emerging diseases 93.1 Import risk analysis (IRA) 103.2 Aquaculture and disease emergence 113.3 Climate change and disease emergence 133.4 Outbreak investigations 134 Surveillance and surveys 154.1 Investigation of disease prevalence 154.2 Developments in surveillance methodology 164.2.1 Risk-based surveillance and scenario tree modelling 164.2.2 Spatial and temporal analysis 164.3 Test validation 175 Spread, establishment and impact of pathogens 185.1 Identifying routes of spread 185.1.1 Ex-ante studies of disease spread 195.1.2 Ex-post observational studies 215.2 Identifying risk factors for disease establishment 235.3 Assessing impact at the population level 245.3.1 Recording mortality 245.3.2 Farm health and production records 265.3.3 Assessing the impact of disease in wild populations 276 Conclusions 317 Competing interests 328 Authors' contributions 329 Acknowledgements 3310 References 33

Infectious diseases in oyster aquaculture require a new integrated approach

“…In Australia, the Department of Primary Industries in New South Wales adopted a disease response plan which involved quarantine and prevention of oyster movements from the affected rivers [57]. Other biosecurity measures, such as minimizing the exchanges of stock, personnel and equipment between farming areas help to limit the introduction or the spread of pathogens in finfish [28,80] and are recommended for bivalve farming [57].…”

Mass mortalities of Pacific oysters Crassostrea gigas reflect infectious diseases and vary with farming practices in the Mediterranean Thau lagoon, France

“…Ecologically and economically important invertebrates have been affected by large-scale mass mortalities, generally related to infectious diseases (Mydlarz et al 2006). In aquaculture species, numerous diseases have emerged through pathogen exchange with wild populations, evolution of pathogenic from nonpathogenic microorganisms and anthropogenic transfer of stocks (Murray & Peeler 2005, Peeler & Taylor 2011. Characteristics of the aquaculture environment, such as hydrodynamic connectivity, mixing of waters and close proximity, exacerbate disease epidemics (McCallum et al 2004, Gustafson et al 2007, Viljugrein et al 2009, Salama & Murray 2011.…”

Influence of Maternal and Larval Immunisation against <i>Lactococcus garviae</i> Infection in Rainbow Trout <i>Oncorhynchus mykiss</i> (Walaum) Lysozyme Activity and IgM Level

“…The aquaculture industry is recently facing a serious setback due to infectious [23] diseases leading to severe economic loss [24]. Although mortalities have been reported in all stages of life, maximum mortalities in all the cultivated fish species have been reported at larval stages.…”