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1.
J Fish Dis ; 45(6): 919-930, 2022 Jun.
Article in English | MEDLINE | ID: mdl-35397120

ABSTRACT

An incursion of infectious salmon anaemia virus (ISAV) was detected in 2020 in southern Newfoundland, Canada. This resulted in an outbreak affecting four marine farms stocking Atlantic salmon (Salmo salar L.) vaccinated against ISAV. This study provides the first description of epidemiologic characteristics of an ISAV outbreak in 2020 and 2021, and detected ISAV variants at the population level. Fish kidneys were screened for ISAV by real-time RT-PCR and non-negative samples were submitted for genotyping and further diagnostic testing. Nine distinct ISAV variants were identified: five European and three North American (NA) HPRΔ ISAV, and one NA-HPR0 ISAV variant. A notable finding was the concurrent detection of both an HPR0 and an HPRΔ ISAV variant in one individual fish. In two farms, both European and NA variants were simultaneously detected, while in the other two farms either NA or European variants were identified, but not both together. Generally, mortality increases followed rises in ISAV prevalence and cycle threshold values on RT-PCR decreased with time. Epidemiologic descriptions of ISAV outbreaks in Atlantic Canada contributes to the understanding of local disease dynamics and identification of changes thereof. Such insights are essential for the strengthening of disease management plans.


Subject(s)
Fish Diseases , Isavirus , Orthomyxoviridae Infections , Salmo salar , Animals , Canada , Fish Diseases/epidemiology , Isavirus/genetics , Newfoundland and Labrador , Orthomyxoviridae Infections/epidemiology , Orthomyxoviridae Infections/veterinary , Phylogeny
2.
Transbound Emerg Dis ; 69(4): 2029-2044, 2022 Jul.
Article in English | MEDLINE | ID: mdl-34152091

ABSTRACT

Simulation models are useful tools to predict and elucidate the effects of factors influencing the occurrence and spread of epidemics in animal populations, evaluate the effectiveness of different control strategies and ultimately inform decision-makers about mitigations to reduce risk. There is a paucity of simulation models to study waterborne transmission of viral and bacterial pathogens in marine environments. We developed a stochastic, spatiotemporal hybrid simulation model (DTU-DADS-Aqua) that incorporates a compartmental model for infection spread within net-pens, an agent-based model for infection spread between net-pens within and between sites and uses seaway distance to inform farm-site hydroconnectivity. The model includes processes to simulate infection transmission and control over surveillance, detection and depopulation measures. Different what-if scenarios can be explored according to the input data provided and user-defined parameter values, such as daily surveillance and depopulation capacities or increased animal mortality that triggers diagnostic testing to detect infection. The latter can be easily defined in a software application, in which results are summarized after each simulation. To demonstrate capabilities of the model, we simulated the spread of infectious salmon anaemia virus (ISAv) for realistic scenarios in a transboundary population of farmed Atlantic salmon (Salmo salar L.) in New Brunswick, Canada and Maine, United States. We assessed the progression of infection in the different simulated outbreak scenarios, allowing for variation in the control strategies adopted for ISAv. Model results showed that improved disease detection, coupled with increasing surveillance visits to farm-sites and increased culling capacity for depopulation of infected net-pens reduced the number of infected net-pens and outbreak duration but the number of ISA-infected farm sites was minimally affected. DTU-DADS-Aqua is a flexible modelling framework, which can be applied to study different infectious diseases in the aquatic environment, allowing the incorporation of alternative transmission and control dynamics. The framework is open-source and available at https://github.com/upei-aqua/DTU-DADS-Aqua.


Subject(s)
Fish Diseases , Isavirus , Orthomyxoviridae Infections , 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid/analogs & derivatives , Animals , Aquaculture , Orthomyxoviridae Infections/epidemiology , Orthomyxoviridae Infections/veterinary
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