Modelling transmission of Perkinsus marinus (Dermo disease)
Transmission of Perkinsus marinus from a central outer oyster reef to other reefs along a model tidal estuary. 2D view. The model is a biophysical model. We coupled a biological/disease model into ROMS model.
Bidegain, G., Klinck, J.M., Levin, J., Powell, E.N., Haidvogel, D., Ben-Horin, T., Hofmann, E.E. 2016. A coupled benthic-circulation model for Dermo disease in the eastern oyster Crassostrea virginica. Aquaculture 2016, World Aquaculture Society Meeting. Las Vegas, NV, USA.
Transmission of Perkinsus marinus from a central outer oyster reef to other reefs along a model tidal estuary. 2D view. The model is a biophysical model. We coupled a biological/disease model into ROMS model.
Bidegain, G., Klinck, J.M., Levin, J., Powell, E.N., Haidvogel, D., Ben-Horin, T., Hofmann, E.E. 2016. A coupled benthic-circulation model for Dermo disease in the eastern oyster Crassostrea virginica. Aquaculture 2016, World Aquaculture Society Meeting. Las Vegas, NV, USA.
Modelling the transmission of Perkinsus marinus in oysters
Dermo disease caused by the protistan Perkinsus marinus in Eastern oysters Crassotrea virginica is an important source of mortality impacting oyster population dynamics resulting in substantial losses in fisheries and aquaculture. The rapid transmission and spread of the disease minimized the importance of transmission models and past models (proliferation-based models) assumed simple density-dependent transmission or rapid infection post-settlement. This approach is a good approximation only for low population densities. A transmission model was developed for P. marinus in Eastern oysters that accounts for the seasonal change in disease dynamics and density-dependent foraging (of suspended particles) interference among hosts. The model, verified and evaluated against field observations, incorporates parasite release to the water column from live and dead individuals, parasite consumption by living oysters, the diffusion of parasites in the water, body burden-based dose-dependent transmission, recruitment, and disease-caused mortality. The model returns a basic reproduction number R0 for Dermo much greater than unity (R0 = 90) in accordance with the current persistence and pandemic nature of this disease in oysters. No population density is obtained that is low enough to suppress R0 below 1 (i.e. disease extinction). R0 is also estimated for high oyster densities (>300 individuals m−2) and particularly for relatively large oysters (∼90 mm), today rare but once common before generalized overfishing occurred on healthy oyster reefs. In this scenario, R0 drops below 1, indicating that high oyster density can limit disease invasion through foraging interference and depletion of parasites in the water column. High intensity recruitment events allow the oyster population to attain such densities and limit the development of epizootics. These results provide insight into the transition from past populations, where Dermo is inferred to have been limited in its impact, to the current persistent and pandemic nature of this disease. Further coupling of this model into metapopulation and hydrodynamic models could be a promising tool to support management decision-making for bivalve populations impacted by Dermo disease. More details in Bidegain et al. 2017 Fisheries Research 186, 82-93.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann, David Bushek, Daphne Munroe, Susan Ford, Ximing Guo.
Funding: National Science Foundation (NSF) program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Theoretical basis for modelling the transmission of marine infectious diseases
Disease-causing organisms can have significant impacts on marine species and communities. However, the dynamics that underlie the emergence of disease outbreaks in marine ecosystems still lack the equivalent level of description, conceptual understanding, and modeling context routinely present in the terrestrial systems. Here, we propose a theoretical basis for modeling the transmission of marine infectious diseases (MIDs) developed from simple models of the spread of infectious disease. The models represent the dynamics of a variety of host-pathogen systems including those unique to marine systems where transmission of disease is by contact with waterborne pathogens both directly and through filter-feeding processes. Overall, the analysis of the epizootiological models focused on the most relevant processes that interact to drive the initiation and termination of epizootics. A priori , systems with multi-step disease infections (e.g., infection-death-particle release-filtration-transmission) reduced dependence on individual parameters resulting in inherently slower transmissions rates. This is demonstrably not the case; thus, these alternative transmission pathways must also considerably increase the rates of processes involved in transmission. Scavengers removing dead infected animals may inhibit disease spread in both contact-based and waterborne pathogen-based diseases. The capacity of highly infected animals, both alive and dead, to release a substantial number of infective elements into the water column, making them available to suspension feeders results in such diseases being highly infective with a very small 'low-abundance refuge'. In these systems, the body burden of pathogens and the relative importance between the release and the removal rate of pathogens in the host tissue or water column becomes paramount. Two processes are of potential consequence inhibiting epizootics. First, large water volumes above the benthic susceptible populations can function as a sink for pathogens. Second, unlike contact-based disease models in which an increase in the number of susceptible individuals in the population increases the likelihood of transmission and epizootic development, large populations of filter feeders can reduce this likelihood through the overfiltration of infective particles. More details in Bidegain et al. 2016, Ecosphere 7 (4):e01286.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann
Funding: National Science Foundation (NSF) program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Microparasitic disease dynamics in benthic suspension feeders
Benthic suspension-feeders can accumulate substantial numbers of microparasitic pathogens by contacting or filtering particles while feeding, thus making them highly vulnerable to infectious diseases. The study of disease dynamics in these marine organism requires an innovative approach to modeling. To do so, we developed a single-population deterministic compartmental model adapted from the mathematical theory of epidemics. The model is a continuous-time model, unstructured in spatial or age terms and configured to simulate the dynamics of diverse dose (body burden)–dependent infectious disease transmission processes in suspension feeders caused by susceptible individuals contacting or absorbing (filtering) infectious waterborne pathogens. Different scenarios were simulated to explore the effect of recruitment, filtration rate, particle loss, diffusion-like processes in the water column and non-focal hosts (i.e. non-susceptible in terms of disease) on disease incidence. An increase in recruitment (i.e. new disease free susceptibles) can reduce the prevalence of infection due to the dilution effect of adding more susceptibles, but the disease can spread faster for the same reason. Lower infective particle accumulation rates or increasing particle loss rates in the environment reduce the prevalence of infection. This effect is trivial when the water is saturated with infective particles released by infected and/or dead animals. Diffusion of particles from the local pool available to suspension feeders to the adjacent remote pool, prompted by a large remote volume and high particle exchange, limits epizootic development. Similarly, the likelihood of an epizootic can be constrained in a large susceptible population when competition for pathogens, more ’active’ in active filter feeders than in passive suspension feeders, reduces the per capita infective particle accumulation rate. In passive suspension feeders, decreasing the area of the feeding surface has the same effect in constraining disease development. The effect of competition for infective particles in essence diluting the infective particle concentration in the water column is magnified when the susceptible population is part of a community with non-focal filter feeders, and is particularly effective in limiting disease development in high infective dose systems. At the same time, this active foraging strategy makes filter feeders more vulnerable to epizootics. The model is a suitable framework for studying the disease dynamics and determinants of disease outbreaks in benthic suspension feeders. More details in Bidegain et al. 2016, Ecological Modelling 328, 44-61.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Fishing diseased species to promote yield and conservation
Past theoretical models suggest fishing disease-impacted stocks can reduce parasite transmission, but this is a good management strategy only when the exploitation required to reduce transmission does not overfish the stock. We applied this concept to a red abalone fishery so impacted by an infectious disease (withering syndrome) that stock densities plummeted and managers closed the fishery. In addition to the non-selective fishing strategy considered by past disease-fishing models,we modelled targeting (culling) infected individuals,whic is plausible in red abalone because modern diagnostic tools can determine infection without harming landed abalone and the diagnostic cost is minor relative to the catch value. The non-selective abalone fishing required to eradicate parasites exceeded thresholds for abalone sustainability, but targeting infected abalone allowed the fishery to generate yield and reduce parasite prevalence while maintaining stock densities at or above the densities attainable if the population was closed to fishing. The effect was strong enough that stock and yield increased even when the catch was one-third uninfected abalone. These results could apply to other fisheries as the diagnostic costs decline relative to catch value. More details in the paper Ben-Horin et al 2016. Phil.Trans.Soc.B. and the poster presented at Aquaculture 2016.
Collaborators: Tal Ben-Horin, Kevin Lafferty, Hunter Lenihan.
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220) and a standard cooperative agreement (SCA no. 58-1915-1-156) between the US Department of Agriculture Agricultural Research Service and the University of Rhode Island
Parasite transmission through suspension feeding
Suspension-feeding bivalve molluscs are confronted with a wide range of materials in the benthic marine environment. These materials include various sized plankton and the organic material derived from it, macroalgae, detritus and a diversity of microbial parasites that have adapted life stages to survive in the water column. For bivalve parasites to infect hosts though, they must first survive and remain infectious in the water column to make initial contact with hosts, and once in contact, enter and overcome elaborate pathways for particle sorting and selection. Even past these defenses, bivalve parasites are challenged with efficient systems of mechanical and chemical digestion and highly evolved systems of innate immunity. Here we review how bivalve parasites evade these hurdles to complete their life
cycles and establish within bivalve hosts. We broadly cover significant viral, bacterial, and protozoan parasites of marine bivalve molluscs, and illustrate the emergent properties of these host-parasite systems where parasite transmission occurs through suspension feeding. Ben-Horin et al. 2015. Journal of Invertebrate Pathology 131, 155-176.
Collaborators: Tal Ben-Horin, Lauren Huey, Diego Nárvaez, David Bushek
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220), NSF Research Experience for Undergraduates supplement to OCE-1216220, and MINECON – NC120086 (Chile).
Dermo disease caused by the protistan Perkinsus marinus in Eastern oysters Crassotrea virginica is an important source of mortality impacting oyster population dynamics resulting in substantial losses in fisheries and aquaculture. The rapid transmission and spread of the disease minimized the importance of transmission models and past models (proliferation-based models) assumed simple density-dependent transmission or rapid infection post-settlement. This approach is a good approximation only for low population densities. A transmission model was developed for P. marinus in Eastern oysters that accounts for the seasonal change in disease dynamics and density-dependent foraging (of suspended particles) interference among hosts. The model, verified and evaluated against field observations, incorporates parasite release to the water column from live and dead individuals, parasite consumption by living oysters, the diffusion of parasites in the water, body burden-based dose-dependent transmission, recruitment, and disease-caused mortality. The model returns a basic reproduction number R0 for Dermo much greater than unity (R0 = 90) in accordance with the current persistence and pandemic nature of this disease in oysters. No population density is obtained that is low enough to suppress R0 below 1 (i.e. disease extinction). R0 is also estimated for high oyster densities (>300 individuals m−2) and particularly for relatively large oysters (∼90 mm), today rare but once common before generalized overfishing occurred on healthy oyster reefs. In this scenario, R0 drops below 1, indicating that high oyster density can limit disease invasion through foraging interference and depletion of parasites in the water column. High intensity recruitment events allow the oyster population to attain such densities and limit the development of epizootics. These results provide insight into the transition from past populations, where Dermo is inferred to have been limited in its impact, to the current persistent and pandemic nature of this disease. Further coupling of this model into metapopulation and hydrodynamic models could be a promising tool to support management decision-making for bivalve populations impacted by Dermo disease. More details in Bidegain et al. 2017 Fisheries Research 186, 82-93.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann, David Bushek, Daphne Munroe, Susan Ford, Ximing Guo.
Funding: National Science Foundation (NSF) program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Theoretical basis for modelling the transmission of marine infectious diseases
Disease-causing organisms can have significant impacts on marine species and communities. However, the dynamics that underlie the emergence of disease outbreaks in marine ecosystems still lack the equivalent level of description, conceptual understanding, and modeling context routinely present in the terrestrial systems. Here, we propose a theoretical basis for modeling the transmission of marine infectious diseases (MIDs) developed from simple models of the spread of infectious disease. The models represent the dynamics of a variety of host-pathogen systems including those unique to marine systems where transmission of disease is by contact with waterborne pathogens both directly and through filter-feeding processes. Overall, the analysis of the epizootiological models focused on the most relevant processes that interact to drive the initiation and termination of epizootics. A priori , systems with multi-step disease infections (e.g., infection-death-particle release-filtration-transmission) reduced dependence on individual parameters resulting in inherently slower transmissions rates. This is demonstrably not the case; thus, these alternative transmission pathways must also considerably increase the rates of processes involved in transmission. Scavengers removing dead infected animals may inhibit disease spread in both contact-based and waterborne pathogen-based diseases. The capacity of highly infected animals, both alive and dead, to release a substantial number of infective elements into the water column, making them available to suspension feeders results in such diseases being highly infective with a very small 'low-abundance refuge'. In these systems, the body burden of pathogens and the relative importance between the release and the removal rate of pathogens in the host tissue or water column becomes paramount. Two processes are of potential consequence inhibiting epizootics. First, large water volumes above the benthic susceptible populations can function as a sink for pathogens. Second, unlike contact-based disease models in which an increase in the number of susceptible individuals in the population increases the likelihood of transmission and epizootic development, large populations of filter feeders can reduce this likelihood through the overfiltration of infective particles. More details in Bidegain et al. 2016, Ecosphere 7 (4):e01286.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann
Funding: National Science Foundation (NSF) program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Microparasitic disease dynamics in benthic suspension feeders
Benthic suspension-feeders can accumulate substantial numbers of microparasitic pathogens by contacting or filtering particles while feeding, thus making them highly vulnerable to infectious diseases. The study of disease dynamics in these marine organism requires an innovative approach to modeling. To do so, we developed a single-population deterministic compartmental model adapted from the mathematical theory of epidemics. The model is a continuous-time model, unstructured in spatial or age terms and configured to simulate the dynamics of diverse dose (body burden)–dependent infectious disease transmission processes in suspension feeders caused by susceptible individuals contacting or absorbing (filtering) infectious waterborne pathogens. Different scenarios were simulated to explore the effect of recruitment, filtration rate, particle loss, diffusion-like processes in the water column and non-focal hosts (i.e. non-susceptible in terms of disease) on disease incidence. An increase in recruitment (i.e. new disease free susceptibles) can reduce the prevalence of infection due to the dilution effect of adding more susceptibles, but the disease can spread faster for the same reason. Lower infective particle accumulation rates or increasing particle loss rates in the environment reduce the prevalence of infection. This effect is trivial when the water is saturated with infective particles released by infected and/or dead animals. Diffusion of particles from the local pool available to suspension feeders to the adjacent remote pool, prompted by a large remote volume and high particle exchange, limits epizootic development. Similarly, the likelihood of an epizootic can be constrained in a large susceptible population when competition for pathogens, more ’active’ in active filter feeders than in passive suspension feeders, reduces the per capita infective particle accumulation rate. In passive suspension feeders, decreasing the area of the feeding surface has the same effect in constraining disease development. The effect of competition for infective particles in essence diluting the infective particle concentration in the water column is magnified when the susceptible population is part of a community with non-focal filter feeders, and is particularly effective in limiting disease development in high infective dose systems. At the same time, this active foraging strategy makes filter feeders more vulnerable to epizootics. The model is a suitable framework for studying the disease dynamics and determinants of disease outbreaks in benthic suspension feeders. More details in Bidegain et al. 2016, Ecological Modelling 328, 44-61.
Collaborators: Eric Powell, John Klinck, Tal Ben-Horin, Eileen Hoffmann
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220).
Fishing diseased species to promote yield and conservation
Past theoretical models suggest fishing disease-impacted stocks can reduce parasite transmission, but this is a good management strategy only when the exploitation required to reduce transmission does not overfish the stock. We applied this concept to a red abalone fishery so impacted by an infectious disease (withering syndrome) that stock densities plummeted and managers closed the fishery. In addition to the non-selective fishing strategy considered by past disease-fishing models,we modelled targeting (culling) infected individuals,whic is plausible in red abalone because modern diagnostic tools can determine infection without harming landed abalone and the diagnostic cost is minor relative to the catch value. The non-selective abalone fishing required to eradicate parasites exceeded thresholds for abalone sustainability, but targeting infected abalone allowed the fishery to generate yield and reduce parasite prevalence while maintaining stock densities at or above the densities attainable if the population was closed to fishing. The effect was strong enough that stock and yield increased even when the catch was one-third uninfected abalone. These results could apply to other fisheries as the diagnostic costs decline relative to catch value. More details in the paper Ben-Horin et al 2016. Phil.Trans.Soc.B. and the poster presented at Aquaculture 2016.
Collaborators: Tal Ben-Horin, Kevin Lafferty, Hunter Lenihan.
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220) and a standard cooperative agreement (SCA no. 58-1915-1-156) between the US Department of Agriculture Agricultural Research Service and the University of Rhode Island
Parasite transmission through suspension feeding
Suspension-feeding bivalve molluscs are confronted with a wide range of materials in the benthic marine environment. These materials include various sized plankton and the organic material derived from it, macroalgae, detritus and a diversity of microbial parasites that have adapted life stages to survive in the water column. For bivalve parasites to infect hosts though, they must first survive and remain infectious in the water column to make initial contact with hosts, and once in contact, enter and overcome elaborate pathways for particle sorting and selection. Even past these defenses, bivalve parasites are challenged with efficient systems of mechanical and chemical digestion and highly evolved systems of innate immunity. Here we review how bivalve parasites evade these hurdles to complete their life
cycles and establish within bivalve hosts. We broadly cover significant viral, bacterial, and protozoan parasites of marine bivalve molluscs, and illustrate the emergent properties of these host-parasite systems where parasite transmission occurs through suspension feeding. Ben-Horin et al. 2015. Journal of Invertebrate Pathology 131, 155-176.
Collaborators: Tal Ben-Horin, Lauren Huey, Diego Nárvaez, David Bushek
Funding: NSF program in Ecology and Evolution of Infectious Diseases (OCE-1216220), NSF Research Experience for Undergraduates supplement to OCE-1216220, and MINECON – NC120086 (Chile).
Modelling Ruditapes sp larval vertical behaviour
The green and the red points are two examples of tracked larvae (the red one starting from the bottom and the green one starting from the surface). The grey blackish particles cloud represents the larval pool.
More info: Bidegain, G., Bárcena, J.F., Juanes, J.A. 2013. LARVAHS: Predicting clam larval dispersal and recruitment using habitat suitability-based particle tracking model. Ecological Modeling 268, 78-92. doi: http://dx.doi.org/10.1016/j.ecolmodel.2013.07.020
The green and the red points are two examples of tracked larvae (the red one starting from the bottom and the green one starting from the surface). The grey blackish particles cloud represents the larval pool.
More info: Bidegain, G., Bárcena, J.F., Juanes, J.A. 2013. LARVAHS: Predicting clam larval dispersal and recruitment using habitat suitability-based particle tracking model. Ecological Modeling 268, 78-92. doi: http://dx.doi.org/10.1016/j.ecolmodel.2013.07.020
Modelling Ruditapes sp larval dipersal
An example of larval dispersal under the effect of tidal force. The example represents the tracking of larval pools coming from two different spawning areas (grey and black particles) in the Bay of Santander (N Spain).
More info: Bidegain, G., Bárcena, J.F., Juanes, J.A. 2013. LARVAHS: Predicting clam larval dispersal and recruitment using habitat suitability-based particle tracking model. Ecological Modeling 268, 78-92. doi: http://dx.doi.org/10.1016/j.ecolmodel.2013.07.020
An example of larval dispersal under the effect of tidal force. The example represents the tracking of larval pools coming from two different spawning areas (grey and black particles) in the Bay of Santander (N Spain).
More info: Bidegain, G., Bárcena, J.F., Juanes, J.A. 2013. LARVAHS: Predicting clam larval dispersal and recruitment using habitat suitability-based particle tracking model. Ecological Modeling 268, 78-92. doi: http://dx.doi.org/10.1016/j.ecolmodel.2013.07.020
Modelling habitat suitability of marine invertebrates (clams, barnacles)
We predicted the habitat suitability for non-indigenous clams to explore the potential for expansion (Bay of Santander, N Spain).
We used this habitat suitability to build our coupled larval dispersal biophysical model.
See more info in: Bidegain, G., Bárcena, J.F., García, A., Juanes, J.A. 2015. Predicting coexistence and predominance patterns between the introduced Manila clam (Ruditapes philippinarum) and the European native clam (Rudi- tapes decussatus). Estuarine Coastal and Shelf Science 152, 162-172. doi: http://dx.doi.org/10.1016/j.ecss.2014.11.018
We predicted the habitat suitability for non-indigenous clams to explore the potential for expansion (Bay of Santander, N Spain).
We used this habitat suitability to build our coupled larval dispersal biophysical model.
See more info in: Bidegain, G., Bárcena, J.F., García, A., Juanes, J.A. 2015. Predicting coexistence and predominance patterns between the introduced Manila clam (Ruditapes philippinarum) and the European native clam (Rudi- tapes decussatus). Estuarine Coastal and Shelf Science 152, 162-172. doi: http://dx.doi.org/10.1016/j.ecss.2014.11.018