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40 results on '"Green, Darren M."'

13. The Contact Structure of Great Britain's Salmon and Trout Aquaculture Industry

Author

Jones, Anne E, Munro, Lorna A, Green, Darren M, Morgan, Kenton L, Murray, Alexander G, Norman, Rachel, Salama, Nabeil K G, Ryder, David, Taylor, Nick G H, Thrush, Mark A, Wallace, I Stuart, and Sharkey, Kieran J

Subjects
giant component, network, fish diseases, Aquaculture, graph, control policy
Abstract

We analyse the network structure of the British salmonid aquaculture industry from the perspective of infectious disease control. We combine for the first time live fish transport (or movement) data covering England and Wales with data covering Scotland and include network layers representing potential transmission by rivers, sea water and local transmission via human or animal vectors in the immediate vicinity of each farm or fishery site. We find that 7.2% of all live fish transports cross the England-Scotland border and network analysis shows that 87% of English and Welsh sites and 72% of Scottish sites are reachable from cross-border connections via live fish transports alone. Consequently, from a disease-control perspective, the contact structures of England and Wales and of Scotland should not be considered in isolation. We also show that large epidemics require the live fish movement network and so control strategies targeting movements can be very effective. While there is relatively low risk of widespread epidemics on the live fish transport network alone, the potential risk is substantially amplified by the combined interaction of multiple network layers.

Published
2019

19. Review of climate change impacts on marine aquaculture in the UK and Ireland

Author

Callaway, Ruth, primary, Shinn, Andrew P., additional, Grenfell, Suzanne E., additional, Bron, James E., additional, Burnell, Gavin, additional, Cook, Elizabeth J., additional, Crumlish, Margaret, additional, Culloty, Sarah, additional, Davidson, Keith, additional, Ellis, Robert P., additional, Flynn, Kevin J., additional, Fox, Clive, additional, Green, Darren M., additional, Hays, Graeme C., additional, Hughes, Adam D., additional, Johnston, Erin, additional, Lowe, Christopher D., additional, Lupatsch, Ingrid, additional, Malham, Shelagh, additional, Mendzil, Anouska F., additional, Nickell, Thom, additional, Pickerell, Tom, additional, Rowley, Andrew F., additional, Stanley, Michele S., additional, Tocher, Douglas R., additional, Turnbull, James F., additional, Webb, Gemma, additional, Wootton, Emma, additional, and Shields, Robin J., additional

Published
2012
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36. The effect of network mixing patterns on epidemic dynamics and the efficacy of disease contact tracing

Author

Kiss, Istvan Z, Green, Darren M, and Kao, Rowland R

Abstract

In networks, nodes may preferentially contact other nodes with similar (assortatively mixed) or dissimilar (disassortatively mixed) numbers of contacts. Different patterns of contact support different epidemic dynamics, potentially affecting the efficacy of control measures such as contact tracing, which aims to identify and isolate nodes with infectious contacts. We used stochastic simulations to investigate the effects of mixing patterns on epidemic dynamics and contact-tracing efficacy. For uncontrolled epidemics, outbreaks occur at lower infection rates for more assortatively mixed networks, with faster initial epidemic growth rate and shorter epidemic duration than for disassortatively mixed networks. Contact tracing performs better for assortative mixing where epidemic size is large and tracing rate low, but it performs better for disassortative mixing at higher contact rates. For assortatively mixed networks, disease spreads first to highly connected nodes, but this is balanced by contact tracing quickly identifying these same nodes. The converse is true for disassortative mixing, where both disease and tracing are less likely to target highly connected nodes. For small epidemics, contact tracing is more effective on disassortative networks due to the greater resilience of assortative networks to link removal. Multi-step contact tracing is more effective than single-step tracing for assortative mixing, but this effect is smaller for disassortatively mixed networks.

Published
2008
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37. Infectious disease control using contact tracing in random and scale-free networks

Author

Kiss, Istvan Z, Green, Darren M, and Kao, Rowland R

Abstract

Contact tracing aims to identify and isolate individuals that have been in contact with infectious individuals. The efficacy of contact tracing and the hierarchy of traced nodes—nodes with higher degree traced first—is investigated and compared on random and scale-free (SF) networks with the same number of nodes Nand average connection K. For values of the transmission rate larger than a threshold, the final epidemic size on SF networks is smaller than that on corresponding random networks. While in random networks new infectious and traced nodes from all classes have similar average degrees, in SF networks the average degree of nodes that are in more advanced stages of the disease is higher at any given time. On SF networks tracing removes possible sources of infection with high average degree. However a higher tracing effort is required to control the epidemic than on corresponding random networks due to the high initial velocity of spread towards the highly connected nodes. An increased latency period fails to significantly improve contact tracing efficacy. Contact tracing has a limited effect if the removal rate of susceptible nodes is relatively high, due to the fast local depletion of susceptible nodes.

Published
2006
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39. Network models of live fish movements and disease spread in Scottish aquaculture

Author

Werkman, Marleen, Turnbull, James F., Green, Darren M., and Murray, Sandy G.

Subjects
Epidemiology, Aquaculture, Live fish movements, Disease spread, Salmon industry Scotland, Fishes Diseases
Abstract

The Scottish salmon industry is facing challenges in the control of aquatic infectious disease, as is the case in other countries such as Chile and Norway. Disease outbreaks can have an enormous economic impact and possibly affect wild fish populations. Disease transmission in an aquatic environment is complex and there are several transmission routes (vertical transmission, natural reservoirs, hydrodynamic transmission and long-distance movements). Effective control methods such as vaccines are not available in all cases and therefore disease prevention remains a priority. In livestock, epidemiological network models have been proven to be a highly useful tool to investigate the role of different transmission routes on the course of epidemics and have the potential to provide the same utility for aquatic networks. Understanding the complex contact network will result in more effective disease prevention, surveillance systems and control strategies. The aim of this thesis was to investigate the Scottish live fish movement network and its consequences for pathogen transmission between farms in order to develop and optimize control strategies for epidemics. The main objective of chapter 3 was to investigate the effect of different fallowing strategies on the spread of diseases with different transmission properties. A network model was constructed that included both local transmission and long-distance transmission. The basic structure of this network was a ring model where neighbours within a management area could infect each other and non-local transmission occurred at random. The results showed that when long-distance transmission was under reasonable control in comparison with local transmission risk, synchronized fallowing at the management area level was potentially a highly effective tool in the control of infectious diseases. Chapter 4 presents a detailed description of the number of live fish movements and their timing for Atlantic salmon (Salmo salar) in Scottish aquaculture. For this, movement records from 2002 to 2004 were provided by Marine Scotland, Aberdeen. Salmon are anadromous and have a freshwater (FW) and seawater phase (SW). Scottish live fish movements can be divided in FW-FW, FW-SW, SW-SW, SW-FW and “other” movements. The latter are mainly movements from and to research sites. This study showed that the contact structure and timing of live fish movements are seasonal and differ largely between production phases. Disease control measures should take these differences into account to optimize their strategies. In chapter 4, live fish movements were shown to be seasonal; therefore in chapter 5 the main aim was to quantify the effects of seasonality of live fish movements on the course of epidemics. The results showed that the sequence of salmon movements is important for the course of an epidemic. Seasonality is important when local transmission is higher than 0.05 per contact per week and when the movements are not clustered and when movements do not occur in a specific order based on the specific assumptions made in this model. In conclusion, this thesis described the complex live fish movement structure of salmon in Scotland and showed that biosecurity in SW farms is good but could be further improved if all management areas apply synchronized fallowing. The results of this study suggest that biosecurity between freshwater sites could be improved by the application of a system similar to management areas in SW farms.

Published
2012

40. Factors affecting variation in mortality of marine Atlantic salmon Salmo salar in Scotland.

Author

Soares S, Murray AG, Crumlish M, Turnbull JF, and Green DM

Subjects
Animals, Birnaviridae Infections mortality, Birnaviridae Infections veterinary, Databases, Factual, Fish Diseases epidemiology, Fish Diseases virology, Infectious pancreatic necrosis virus, Longevity, Models, Biological, Oceans and Seas, Population Dynamics, Risk Factors, Scotland, Seasons, Temperature, Time Factors, Fish Diseases mortality, Salmo salar
Abstract

Databases of site production have an important role to play in the investigation and understanding of diseases, since they store valuable amounts of disease and management data. Diseases pose an important constraint to economic expansion of aquaculture. They are dependent on the complex interacting factors of pathogen, environment, and host, and the causes of death can be related to nutritional, environmental, and genetic factors of the host or infectious agents. We examined the drivers of mortality from a single site-production database, which represented one-third of Scottish farmed salmon Salmo salar L. production in 2005, to determine whether mortality 'benchmarking' data could be generalised across sites and production cycles. We show that farm mortality records play an important role in studying mortality losses and identifying of management problems in production. We found that mortalities varied across the months of the year and with the time of year of initial stocking. Production cycles that started in the third quarter of the year had the highest mortality overall. Furthermore, we found site-to-site variation in mortality that may have been caused by either random occurrence of epidemics and environmental events or other local effects.

Published
2013
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