DAO 106:7-16 (2013)  -  DOI: https://doi.org/10.3354/dao02639

Within-farm spread of infectious salmon anemia virus (ISAV) in Atlantic salmon Salmo salar farms in Chile

F. O. Mardones1,2,*, P. A. Jansen3, P. Valdes-Donoso1, M. Jarpa4, T. M. Lyngstad3, D. Jimenez3, T. E. Carpenter1,5, A. M. Perez1,6

1Center for Animal Disease Modeling and Surveillance (CADMS), Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA
2EpiVet Consulting, Av. Chile-Españo 218, Santiago 7770494, Chile
3Norwegian Veterinary Institute, PO Box 750, Sentrum, 0106 Oslo, Norway
4National Fisheries Services (Sernapesca), Victoria 2832, Valparaíso 2340159, Chile
5EpiCentre and Infectious Disease Research Centre, Massey University, Palmerston North 4442, New Zealand
6CONICET and Facultad de Ciencias Veterinarias UNR, RA-2170 Casilda, Santa Fe, Argentina

ABSTRACT: Spread of infectious salmon anemia virus (ISAV) at the cage level was quantified using a subset of data from 23 Atlantic salmon Salmo salar farms located in southern Chile. Data collected from official surveillance activities were systematically organized to obtain detailed information on infectious salmon anemia (ISA) outbreaks. Descriptive statistics for outbreak duration, proportion of infected fish, and time to secondary infection were calculated to quantify the magnitude of ISAV incursions. Linear and multiple failure time (MFT) regression models were used to determine factors associated with the cage-level reproduction number (Rc) and hazard rate (HR) for recurrent events, respectively. In addition, the Knox test was used to assess if cage-to-cage transmissions were clustered in space and time. Findings suggest that within farms, ISA outbreaks, on average, lasted 30 wk (median = 26 wk, 95% CI = 24 to 37 wk) and affected 57.3% (95% CI = 47.7 to 67.0%) of susceptible cages. The median time to secondarily diagnosed cages was 23 d. Occurrence of clinical ISAV outbreaks was significantly associated with increased Rc, whereas increased HR was significantly associated with clinical outbreaks and with a large number of fish. Spatio-temporal analysis failed to identify clustering of cage cases, suggesting that within-farm ISAV spread is independent of the spatial location of the cages. Results presented here will help to better understand ISAV transmission, to improve the design of surveillance programs in Chile and other regions in which salmon are intensively farmed, and to examine the economic impact of ISAV and related management strategies on various cost and demand shifting factors.

KEY WORDS: Infectious salmon anemia virus · ISAV · Within-farm transmission · Salmon farming · Chile

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Cite this article as: Mardones FO, Jansen PA, Valdes-Donoso P, Jarpa M and others (2013) Within-farm spread of infectious salmon anemia virus (ISAV) in Atlantic salmon Salmo salar farms in Chile. Dis Aquat Org 106:7-16. https://doi.org/10.3354/dao02639

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