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Modelling Infectious Hematopoietic Necrosis Virus Dispersion from Marine Salmon Farms in the Discovery Islands, British Columbia, Canada.

Foreman MG, Guo M, Garver KA, Stucchi D, Chandler P, Wan D, Morrison J, Tuele D - PLoS ONE (2015)

Bottom Line: Numerical particles released from infected farm fish in accordance with IHNV shedding rates estimated through laboratory experiments are dispersed by model oceanic flows.Results demonstrate that neighbouring naïve farms can become exposed to IHNV via water-borne transport from an IHNV diseased farm, with a higher risk in April than July, and that many events in the sequence of farm outbreaks in 2001-2002 are consistent with higher risks in our farm connectivity matrix.Applications to other diseases, transfers between farmed and wild fish, and the effect of vaccinations are also discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Ocean Sciences, Fisheries and Oceans Canada, P.O. Box 6000, Sidney, B.C., V8L 4B2, Canada.

ABSTRACT
Finite volume ocean circulation and particle tracking models are used to simulate water-borne transmission of infectious hematopoietic necrosis virus (IHNV) among Atlantic salmon (Salmo salar) farms in the Discovery Islands region of British Columbia, Canada. Historical simulations for April and July 2010 are carried out to demonstrate the seasonal impact of river discharge, wind, ultra-violet (UV) radiation, and heat flux conditions on near-surface currents, viral dispersion and survival. Numerical particles released from infected farm fish in accordance with IHNV shedding rates estimated through laboratory experiments are dispersed by model oceanic flows. Viral particles are inactivated by ambient UV radiation levels and by the natural microbial community at rates derived through laboratory studies. Viral concentration maps showing temporal and spatial changes are produced and combined with lab-determined minimum infectious dosages to estimate the infective connectivity among farms. Results demonstrate that neighbouring naïve farms can become exposed to IHNV via water-borne transport from an IHNV diseased farm, with a higher risk in April than July, and that many events in the sequence of farm outbreaks in 2001-2002 are consistent with higher risks in our farm connectivity matrix. Applications to other diseases, transfers between farmed and wild fish, and the effect of vaccinations are also discussed.

No MeSH data available.


Related in: MedlinePlus

Percentage of hours when the viral concentrations arising from worst case (red) and vaccinated (blue) scenario disease outbreaks at (shedding) farms in April (upper line) and July (lower line) exceed minimum infective dose thresholds at nearby (receiving) unvaccinated farms.See Fig 1 for farm locations. Shedding farms are along the y-axis and receiving farms along the x-axis. Blanks denote zero, decimal places are only shown for nonzero values less than 1, and diagonal (100%) values are shaded in light blue. Boxes with at least one value larger than 20%, 10% and 3% are shaded in orange, yellow, and pink, respectively.
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pone.0130951.g006: Percentage of hours when the viral concentrations arising from worst case (red) and vaccinated (blue) scenario disease outbreaks at (shedding) farms in April (upper line) and July (lower line) exceed minimum infective dose thresholds at nearby (receiving) unvaccinated farms.See Fig 1 for farm locations. Shedding farms are along the y-axis and receiving farms along the x-axis. Blanks denote zero, decimal places are only shown for nonzero values less than 1, and diagonal (100%) values are shaded in light blue. Boxes with at least one value larger than 20%, 10% and 3% are shaded in orange, yellow, and pink, respectively.

Mentions: Fig 5 is only presented for illustrative purposes. Similar figures could be produced for other time periods in April and July and all possible combinations of release and receiving farms. The relative risk of water borne transmission between diseased and neighbouring naïve farms can then be quantified by placing average infective cohort counts, like those displayed in Fig 5, into a connectivity table similar to those produced in Table 1 of [13] and Table 2 of [14]. As an example, Fig 6 shows April and July connections risks for the same 13 Discovery farms that were presented in [7]. (Full tables showing connections among all 32 Discovery farms will be generated and made available to industry and FOC Aquaculture Management Division.) In this case, the metric chosen to denote connectivity is the percentage of time over days 6–20 of each month when the concentration in at least one m3 volume within the receiving farm exceeds the minimum infective doses arising from a worst case scenario or vaccinated shedding farm. (For now, the receiving farm is assumed to be unvaccinated but the further risk reduction when it is also vaccinated will be discussed later.) This calculation assumes continuing hourly releases (i.e., no measures were taken to stop the viral shedding) and the 15 day period (as opposed to the full 18-day) was chosen to account for a full spring-neap tidal cycle and for spin-up and spin-down periods when the concentrations were not at relatively steady values.


Modelling Infectious Hematopoietic Necrosis Virus Dispersion from Marine Salmon Farms in the Discovery Islands, British Columbia, Canada.

Foreman MG, Guo M, Garver KA, Stucchi D, Chandler P, Wan D, Morrison J, Tuele D - PLoS ONE (2015)

Percentage of hours when the viral concentrations arising from worst case (red) and vaccinated (blue) scenario disease outbreaks at (shedding) farms in April (upper line) and July (lower line) exceed minimum infective dose thresholds at nearby (receiving) unvaccinated farms.See Fig 1 for farm locations. Shedding farms are along the y-axis and receiving farms along the x-axis. Blanks denote zero, decimal places are only shown for nonzero values less than 1, and diagonal (100%) values are shaded in light blue. Boxes with at least one value larger than 20%, 10% and 3% are shaded in orange, yellow, and pink, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482787&req=5

pone.0130951.g006: Percentage of hours when the viral concentrations arising from worst case (red) and vaccinated (blue) scenario disease outbreaks at (shedding) farms in April (upper line) and July (lower line) exceed minimum infective dose thresholds at nearby (receiving) unvaccinated farms.See Fig 1 for farm locations. Shedding farms are along the y-axis and receiving farms along the x-axis. Blanks denote zero, decimal places are only shown for nonzero values less than 1, and diagonal (100%) values are shaded in light blue. Boxes with at least one value larger than 20%, 10% and 3% are shaded in orange, yellow, and pink, respectively.
Mentions: Fig 5 is only presented for illustrative purposes. Similar figures could be produced for other time periods in April and July and all possible combinations of release and receiving farms. The relative risk of water borne transmission between diseased and neighbouring naïve farms can then be quantified by placing average infective cohort counts, like those displayed in Fig 5, into a connectivity table similar to those produced in Table 1 of [13] and Table 2 of [14]. As an example, Fig 6 shows April and July connections risks for the same 13 Discovery farms that were presented in [7]. (Full tables showing connections among all 32 Discovery farms will be generated and made available to industry and FOC Aquaculture Management Division.) In this case, the metric chosen to denote connectivity is the percentage of time over days 6–20 of each month when the concentration in at least one m3 volume within the receiving farm exceeds the minimum infective doses arising from a worst case scenario or vaccinated shedding farm. (For now, the receiving farm is assumed to be unvaccinated but the further risk reduction when it is also vaccinated will be discussed later.) This calculation assumes continuing hourly releases (i.e., no measures were taken to stop the viral shedding) and the 15 day period (as opposed to the full 18-day) was chosen to account for a full spring-neap tidal cycle and for spin-up and spin-down periods when the concentrations were not at relatively steady values.

Bottom Line: Numerical particles released from infected farm fish in accordance with IHNV shedding rates estimated through laboratory experiments are dispersed by model oceanic flows.Results demonstrate that neighbouring naïve farms can become exposed to IHNV via water-borne transport from an IHNV diseased farm, with a higher risk in April than July, and that many events in the sequence of farm outbreaks in 2001-2002 are consistent with higher risks in our farm connectivity matrix.Applications to other diseases, transfers between farmed and wild fish, and the effect of vaccinations are also discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Ocean Sciences, Fisheries and Oceans Canada, P.O. Box 6000, Sidney, B.C., V8L 4B2, Canada.

ABSTRACT
Finite volume ocean circulation and particle tracking models are used to simulate water-borne transmission of infectious hematopoietic necrosis virus (IHNV) among Atlantic salmon (Salmo salar) farms in the Discovery Islands region of British Columbia, Canada. Historical simulations for April and July 2010 are carried out to demonstrate the seasonal impact of river discharge, wind, ultra-violet (UV) radiation, and heat flux conditions on near-surface currents, viral dispersion and survival. Numerical particles released from infected farm fish in accordance with IHNV shedding rates estimated through laboratory experiments are dispersed by model oceanic flows. Viral particles are inactivated by ambient UV radiation levels and by the natural microbial community at rates derived through laboratory studies. Viral concentration maps showing temporal and spatial changes are produced and combined with lab-determined minimum infectious dosages to estimate the infective connectivity among farms. Results demonstrate that neighbouring naïve farms can become exposed to IHNV via water-borne transport from an IHNV diseased farm, with a higher risk in April than July, and that many events in the sequence of farm outbreaks in 2001-2002 are consistent with higher risks in our farm connectivity matrix. Applications to other diseases, transfers between farmed and wild fish, and the effect of vaccinations are also discussed.

No MeSH data available.


Related in: MedlinePlus