Disease management mitigates risk of pathogen transmission from maricultured salmonids

Abstract

Open marine net pens facilitate virus and sea lice transfer, occasionally leading to infections and outbreaks of disease in farmed salmon. A review of 3 salmon pathogens (infectious salmon anaemia virus [ISAV], salmon alphavirus [SAV] and the salmon louse Lepeophtheirus salmonis) shows that increased risk of exposure to neighbouring farms is inversely related to distance from and directly related to biomass at the source of infection. Epidemiological techniques integrating data from oceanography, diagnostics and pathogen shedding rates and viability contribute to improved understanding of pathogen transmission pathways among farms and permit the designation of areas of risk associated with sources of infection. Occupation of an area of risk may increase the likelihood of exposure, infection and disease among susceptible fish. Disease mitigation in mariculture occurs at 2 scales: area-based (coordinated stocking, harvesting and fallowing) and farm-based (vaccination, early pathogen detection, veterinary prescribed treatments and depopulation or early harvest in the event of viral disease). Collectively, implementation of mitigation measures results in virus disease outbreaks of shorter duration with lower mortality and therefore reduces the likelihood of pathogen transmission. In contrast, the mitigation of sea lice transmission is less likely to be effective in some areas due to the loss of parasite sensitivity to therapeutants and to dissemination of larval lice when parasites occur below management thresholds. For wild populations, risk of pathogen spillback is estimated from farm-based epidemiological data; however, validation, particularly for ISAV and SAV, is required using direct surveillance.

Population biology of infectious diseases shared by wild and farmed fish

“…The challenges of infectious disease in fisheries and aquaculture have already spurred innovations to control disease and promote fish health (Pohlenz and Gatlin 2014;Jones et al 2015;Naslund and Johnsson 2016). The obvious example is the production of new pesticides, medicines, and vaccines (Lorenzen and LaPatra 2005;Shoemaker et al 2009).…”

How pathogens affect the marine habitat use and migration of sea trout (Salmo trutta) in two Norwegian fjord systems

“…Fjords in Norway are connected by marine species that migrate and disperse, which can be vectors for pathogens that generate local hot spots in the landscape. Human activities can influence the presence of pathogens and aquaculture operations, for example, importing pathogens or providing a reservoir in which pathogens can thrive and be transmitted to wild fish (Jones, Bruno, Madsen, & Peeler, 2015; Wiik‐Neilsen et al, 2017). More research on the presence and prevalence of these pathogens in wild and farmed salmonids in other Norwegian fjords is important for comparison with our results to develop an understanding of the factors limiting the distribution of relevant salmonid pathogens.…”

A historical review of the key bacterial and viral pathogens of Scottish wild fish

“…() although this disease was not widespread being reported from only a few Scottish river systems (mainly the Aberdeenshire Dee). The concept of pathogen spillback to populations of wild fish is also discussed by Jones, Bruno, Madsen, and Peeler () when considering disease mitigation measures at aquaculture sites.…”