A Preliminary Investigation of the Relationship Between Infected Cage Removal Speed and Resultant Spread of Infectious Salmon Anemia on Atlantic Salmon Farms in Maine, U.S.A., and New Brunswick, Canada

Gustafson, Lori; Ellis, S; Hawkins, Leighanne; Moore, Mark; Robinson, T; MacPhee, D. D.

doi:10.1002/9780470376850.ch12

Cited by 2 publications

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“…Furthermore, the mean depopulation delay of subsequent infected farms was about 3 wk in the Scottish epidemic (Stagg et al 2001, Stagg 2003) compared with 16 wk in the Chilean epidemic. Observations of ISA events in North America showed that early removal of infected cages effectively limits ISAV spread (Gustafson et al 2006) and timely depopulation has been important in the control of other highly infectious diseases such as FMD or AI (Howard & Donnelly 2000). Although detailed information to estimate depopulation delays was not available for all ISAV-infected farms in Chile, we believe delayed depopulation may have played an important role in the subsequent spread of ISAV.…”

Section: Discussionmentioning

confidence: 99%

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

Mardones¹,

Pérez²,

Carpenter³

2009

Dis. Aquat. Org.

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Reports from surveillance activities were analyzed to determine the epidemiology of the re-emergence of infectious salmon anemia virus (ISAV) in Atlantic salmon farms in Chile. The epidemic and spatial and spatiotemporal patterns were described, taking into account commercial compartmentalization of the farms. During the 64 wk study period, 76 ISAV-infected salmon farms, representing 17 companies, were reported in 65% of the management geographic zones of the 10th region in southern Chile. Approximately 20% of the farms at risk became infected, with the incidence rate increasing slightly over time. Results from epidemic analyses and observed spatial and spatiotemporal patterns suggested an initial dispersal and subsequent clustering of cases around the index case (IC) in a propagated epidemic mode. Results suggested that delayed depopulation may have been a key factor in the spread and persistence of ISAV. Clustering of cases supported the assumption that passive transmission in seawater from ISAV-infected farms (proximity) is a critical factor in controlling disease. The re-emergence of ISAV in Chile has resulted in one of the largest ISAV epidemics reported in the world and this study generates new hypotheses and provides useful information for spatial disease control planning in salmon farming areas.

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Section: Discussionmentioning

confidence: 99%

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

Mardones¹,

Pérez²,

Carpenter³

2009

Dis. Aquat. Org.

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“…This designation is a precursor to qualification for potential indemnification if cages are eradicated under a State of Maine‐mandated kill order. However, because early removal of positive cages is recognized as a means of improved disease control (Gustafson, Ellis, Hawkins, Moore, Robinson & MacPhee 2006), cages are often emptied voluntarily by producers prior to meeting the criteria for a formal declaration of infection. Consequently, to minimize mis‐classification of positive cages emptied before formal diagnosis, we used the less restrictive case definition of disease as any cage having one or more moribund fish found positive by RT‐PCR, and substantiated in the same fish by corroborating (3+ or 4+) IFAT, cell culture, or North American genotype results.…”

Section: Methodsmentioning

confidence: 99%

Spatial and non‐spatial risk factors associated with cage‐level distribution of infectious salmon anaemia at three Atlantic salmon, Salmo salar L., farms in Maine, USA

Gustafson

Ellis²,

Robinson³

et al. 2007

Journal of Fish Diseases

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The distribution of infectious salmon anaemia (ISA) was examined among 80 cages from three Atlantic salmon grow-out farms in Maine, USA that were stocked with smolts from a single hatchery. Cage-level disease was broadly defined as one or more moribund fish testing positive for infectious salmon anaemia virus (ISAV) by RT-PCR and a second confirmatory test (IFAT, culture or genotype sequence). Spatio-temporal and cage-level risks were explored using logistic regression and survival analysis. Non-spatial risk factors associated with ISA, or shortened survival time to disease, included increased predation, trucking company choice for smolt transfers, a finely-sedimented benthic substrate, and smaller average size of smolts at stocking. Univariable analysis identified the time-dependent spatial factor 'adjacency to newly infected cages' to be predictive of new infection in neighbouring cages 11-12 weeks later. However, none of the spatial factors, or their lags retained relevance in multiple-variable models. The results suggest a diffuse distribution of virus exposure throughout infected sites, with host-susceptibility factors probably influencing disease manifestation in individual cages. The narrow focus of the current study may limit application of the findings to other sites and year-classes. However, these data support the relevance of husbandry efforts to optimize fish health in regions affected by ISAV.

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A Preliminary Investigation of the Relationship Between Infected Cage Removal Speed and Resultant Spread of Infectious Salmon Anemia on Atlantic Salmon Farms in Maine, U.S.A., and New Brunswick, Canada

Cited by 2 publications

References 10 publications

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

Epidemiologic investigation of the re-emergence of infectious salmon anemia virus in Chile

Spatial and non‐spatial risk factors associated with cage‐level distribution of infectious salmon anaemia at three Atlantic salmon, Salmo salar L., farms in Maine, USA

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