Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Estimating host genetic effects on susceptibility and infectivity to infectious diseases and their contribution to response to selection
Anche, M.T. - \ 2016
Wageningen University. Promotor(en): Mart de Jong, co-promotor(en): Piter Bijma. - Wageningen : Wageningen University - ISBN 9789462577442 - 185 p.
livestock - hosts - genetic effects - susceptibility - infectivity - infectious diseases - breeding value - heritability - epidemics - vee - gastheren (dieren, mensen, planten) - genetische effecten - vatbaarheid - infectiviteit - infectieziekten - fokwaarde - epidemieën

Mahlet Teka Anche. (2016). Estimating host genetic effects on susceptibility and infectivity to infectious diseases and their contribution to response to selection. PhD thesis, Wageningen University, the Netherlands

Genetic approaches aiming to reduce the prevalence of an infection in a population usually focus on improving host susceptibility to an infection. The prevalence of an infection, however, is also affected by the infectivity of individuals. Studies reported that there exists among host (genetic/phenotypic) variation in susceptibility and infectivity to infectious diseases. The effect of host genetic variation in susceptibility and infectivity on the prevalence and risk of an infection is usually measured by the value of the basic reproduction ratio, R0. R0 is an important epidemiological parameter that determines the risk and prevalence of an infection. It has a threshold value of 1, where major disease outbreak can occur when R0 > 1 and the disease will die out when R0 < 1. Due to this threshold property, genetic improvements aiming to reduce the prevalence of an infection should focus on reducing R0 to a value below 1. The overall aim of this thesis was to develop methodologies that allow us to investigate the genetic effects of host susceptibility and infectivity on the prevalence of an infection, which is measured by the value of R0. Moreover, we also aim to investigating the effect of relatedness among groupmates on the utilization of among host genetic variation in susceptibility and infectivity so as to reduce the prevalence of infectious diseases. The theory of direct-indirect genetic effects and epidemiological concepts were combined to develop methodologies. In addition, a simulation study was performed to validate the methodologies developed and examine the effect of relatedness on the utilization of genetic variation in susceptibility and infectivity. It was shown that an individual’s genetic effect on its susceptibility and infectivity affect the prevalence of an infection and that an individual’s breeding value for R0 can be defined as a function of its own allele frequencies for susceptibility and infectivity and of population average susceptibility and infectivity. Moreover, simulation results show that, not only an individual’s infectivity but also an individual’s susceptibility represents an indirect genetic effect on the disease status of individuals and on the prevalence of an infection in a population. It was shown that having related groupmates allows breeders to utilize the genetic variation in susceptibility and infectivity, so as to reduce the prevalence of an infection.

Economic assessment of Q fever in the Netherlands
Asseldonk, M.A.P.M. van; Prins, J. ; Bergevoet, R.H.M. - \ 2013
Preventive Veterinary Medicine 112 (2013)1-2. - ISSN 0167-5877 - p. 27 - 34.
vaccination - epidemics - zoonosis - benefits - outbreak - disease - burden
In this paper the economic impact of controlling the Q fever epidemic in 2007-2011 in the Netherlands is assessed. Whereas most of the long-term benefits of the implemented control programme stem from reduced disease burden and human health costs, the majority of short-term intervention costs were incurred in the dairy goat sector. The total intervention cost in agriculture amounted approximately 35,000 Euro per DALY occurred. By culling of infected animals, breeding prohibition and vaccination, the epidemic seems to be under control. As the dairy goat vaccination programme continues, future expenses in maintaining the current protected status are relatively low. (C) 2013 Elsevier B.V. All rights reserved.
The potential of antiviral agents to control classical swine fever: A modelling study.
Backer, J.A. ; Vrancken, R. ; Neyts, J. ; Goris, N. - \ 2013
Antiviral Research 99 (2013)3. - ISSN 0166-3542 - p. 245 - 250.
virus - netherlands - pigs - transmission - vaccination - strategies - epidemics - marker
Classical swine fever (CSF) represents a continuous threat to pig populations that are free of disease without vaccination. When CSF virus is introduced, the minimal control strategy imposed by the EU is often insufficient to mitigate the epidemic. Additional measures such as preemptive culling encounter ethical objections, whereas emergency vaccination leads to prolonged export restrictions. Antiviral agents, however, provide instantaneous protection without inducing an antibody response. The use of antiviral agents to contain CSF epidemics is studied with a model describing within- and between-herd virus transmission. Epidemics are simulated in a densely populated livestock area in The Netherlands, with farms of varying sizes and pig types (finishers, piglets and sows). Our results show that vaccination and/or antiviral treatment in a 2 km radius around an infected herd is more effective than preemptive culling in a 1 km radius. However, the instantaneous but temporary protection provided by antiviral treatment is slightly less effective than the delayed but long-lasting protection offered by vaccination. Therefore, the most effective control strategy is to vaccinate animals when allowed (finishers and piglets) and to treat with antiviral agents when vaccination is prohibited (sows). As independent control measure, antiviral treatment in a 1 km radius presents an elevated risk of epidemics running out of control. A 2 km control radius largely eliminates this risk.
Integrated mosquito larval source management reduces larval numbers in two highland villages in western Kenya
Imbahale, S.S. ; Githeko, A. ; Mukabana, W.R. ; Takken, W. - \ 2012
BMC Public Health 12 (2012). - ISSN 1471-2458
insecticide-treated nets - malaria vector control - dar-es-salaam - microbial larvicides - tanzania - transmission - suppression - epidemics - association - temperature
Background: In western Kenya, malaria remains one of the major health problems and its control remains an important public health measure. Malaria control is by either use of drugs to treat patients infected with malaria parasites or by controlling the vectors. Vector control may target the free living adult or aquatic (larval) stages of mosquito. The most commonly applied control strategies target indoor resting mosquitoes. However, because mosquitoes spend a considerable time in water, targeting the aquatic stages can complement well with existing adult control measures. Methods: Larval source management (LSM) of malaria vectors was examined in two villages i.e. Fort Ternan and Lunyerere, with the aim of testing strategies that can easily be accessed by the affected communities. Intervention strategies applied include environmental management through source reduction (drainage of canals, land levelling or by filling ditches with soil), habitat manipulation (by provision of shading from arrow root plant), application of Bacillus thuringiensis var israelensis (Bti) and the use of predatory fish, Gambusia affinis. The abundance of immature stages of Anopheles and Culex within intervention habitats was compared to that within non-intervention habitats. Results: The findings show that in Fort Ternan no significant differences were observed in the abundance of Anopheles early and late instars between intervention and non-intervention habitats. In Lunyerere, the abundance of Anopheles early instars was fifty five times more likely to be present within non-intervention habitats than in habitats under drainage. No differences in early instars abundance were observed between non-intervention and habitats applied with Bti. However, late instars had 89 % and 91 % chance of being sampled from non-intervention rather than habitats under drainage and those applied with Bti respectively. Conclusion: Most of these interventions were applied in habitats that arose due to human activities. Involvement of community members in control programs would be beneficial in the long term once they understand the role they play in malaria transmission. Apart from the need for communities to be educated on their role in malaria transmission, there is a need to develop and test strategies that can easily be accessed and hence be used by the affected communities. The proposed LSM strategies target outdoor immature mosquitoes and hence can complement well with control measures that target indoor resting vectors. Therefore inclusion of LSM in Integrated Vector Management (IVM) program would be beneficial.
Economic aspects of antiviral agents to control Classical Swine Fever epidemics
Bergevoet, R.H.M. ; Asseldonk, M.A.P.M. van; Backer, J.A. - \ 2012
The Hague : LEI, part of Wageningen UR (Report / LEI : Research area Agriculture &amp; entrepreneurship ) - ISBN 9789086156023
agrarische economie - antivirale middelen - classical swine fever virus - epidemieën - dierziekten - dierziektepreventie - economische aspecten - nederland - agricultural economics - antiviral agents - epidemics - animal diseases - animal disease prevention - economic aspects - netherlands
Outbreaks of contagious animal diseases such as Classical Swine Fever have detrimental effects on the livestock sector in an affected country as well as on society at large. The development of antiviral agents to control these epidemics can reduce the consequences of such outbreaks. The economic impact of applying these antiviral agents is until now unknown. In this report these consequences are investigated.
Vogelgriep ontrafeld : resultaten FES-AI onderzoeksprogramma
Luijkx, D.L.M. ; Scholtens, B. ; Nijland, H.R. - \ 2012
Lelystad : CVI - ISBN 9789461734907 - 62
aviaire influenza - aviaire influenzavirussen - vogels - pluimveehouderij - epidemieën - dierziektepreventie - ziektebestrijding - vaccinatie - diagnostiek - virologie - nederland - avian influenza - avian influenza viruses - birds - poultry farming - epidemics - animal disease prevention - disease control - vaccination - diagnostics - virology - netherlands
Vogelgriep en mensengriep zijn nauwe verwanten: beide worden meestal veroorzaakt door zogeheten Influenza-A-virussen. Zo'n griepvirus is een mini-kikkertje van hooguit honderd nanometer (0,0001 milimeter) doorsnede met eiwituitstulpingen aan de buitenkant. Daarmee klampt het virusbolletje zich vast aan de cellen van zijn gastheer. Die hechting heeft het nodig om de cel te infecteren en zichzelf daarna te kunnen vermenigvuldigen. Dit boekje heeft de vogelgriepuitbraak van 2003 in Nederland als startpunt. Welke dilemma's deden zich toen voor en welke bestrijdingsmogelijkheden waren er voorhanden? Vanwege de twijfels, vragen en onzekerheden werd het FES-AI onderzoeksprogramma in het leven geroepen. Het FES-AI programma is opgedeeld in 7 verschillende kennisvelden. Voor de samenstelling van dit boekje is gesproken met de onderzoekleiders, die het onderzoek vorm hebben gegeven.
Een gezonde discussie : morele en epidemiologische bijdragen voor dierziekten beleid
Stassen, E.N. ; Cohen, N.E. ; Bouma, A. ; Kupper, J.F.H. ; Meijboom, F.L.B. ; Brom, F.W.A. ; Stegeman, J.A. - \ 2011
[S.l.] : NWO [etc.] - 87
dierziektepreventie - dierziekten - epidemiologie - ethiek - mens-dier relaties - epidemieën - dierhouderij - animal disease prevention - animal diseases - epidemiology - ethics - human-animal relationships - epidemics - animal husbandry
Using mortality data for early detection of Classical Swine Fever in The Netherlands
Backer, J.A. ; Brouwer, H. ; Schaik, G. van; Roermund, H.J.W. van - \ 2011
Preventive Veterinary Medicine 99 (2011)1. - ISSN 0167-5877 - p. 38 - 47.
experimental-infection - antibody-response - weaner pigs - virus - transmission - disease - strategies - epidemics - vaccine - marker
Early detection of the introduction of an infectious livestock disease is of great importance to limit the potential extent of an outbreak. Classical Swine Fever (CSF) often causes non-specific clinical signs, which can take considerable time to be detected. Currently, the disease can be detected by three main routes, that are all triggered by clinical signs. To improve the early detection of CSF an additional program, based on mortality data, aims to routinely perform PCR tests on ear notch samples from herds with a high(er) mortality. To assess the effectiveness of this new early detection system, we have developed a stochastic model that describes the virus transmission within a pig herd, the development of disease in infected animals and the different early detection programs. As virus transmission and mortality (by CSF and by other causes) are different for finishing pigs, piglets and sows, a distinction is made between these pig categories. The model is applied to an extensive database that contains all unique pig herds in The Netherlands, their herd sizes and their mortality reports over the CSF-free period 2001-2005. Results from the simulations suggest that the new early detection system is not effective in piglet sections, due to the high mortality from non-CSF causes, nor in sow sections, due to the low CSF-mortality. In finishing herds, the model predicts that the new early detection system can improve the detection time by two days, from 38 (27-53) days to 36(24-51) days after virus introduction, when assuming a moderately virulent virus strain causing a 50% CSF mortality. For this result up to 5 ear notch samples per herd from 8(0-13) finishing herds must be tested every workday. Detecting a source herd two days earlier could considerably reduce the number of initially infected herds. However, considering the variation in outcome and the uncertainty in some model assumptions, this two-day gain in detection time is too small to demonstrate a substantial effect of the new early detection system based on mortality data. But when the alertness of herd-owners and veterinarians diminishes during long CSF-free periods, the new early detection system might gain in effectiveness. (C) 2010 Elsevier B.V. All rights reserved.
Perspectives for geographically oriented management of fusarium mycotoxins in the cereal supply chain
Fels-Klerx, H.J. van der; Booij, C.J.H. - \ 2010
Journal of Food Protection 73 (2010)6. - ISSN 0362-028X - p. 1153 - 1159.
small-grain cereals - wheat head blight - winter-wheat - deoxynivalenol content - prevention strategies - weather data - epidemics - europe - models - maize
This article provides an overview of available systems for management of Fusarium mycotoxins in the cereal grain supply chain, with an emphasis on the use of predictive mathematical modeling. From the state of the art, it proposes future developments in modeling and management and their challenges. Mycotoxin contamination in cereal grain–based feed and food products is currently managed and controlled by good agricultural practices, good manufacturing practices, hazard analysis critical control points, and by checking and more recently by notification systems and predictive mathematical models. Most of the predictive models for Fusarium mycotoxins in cereal grains focus on deoxynivalenol in wheat and aim to help growers make decisions about the application of fungicides during cultivation. Future developments in managing Fusarium mycotoxins should include the linkage between predictive mathematical models and geographical information systems, resulting into region-specific predictions for mycotoxin occurrence. The envisioned geographically oriented decision support system may incorporate various underlying models for specific users’ demands and regions and various related databases to feed the particular models with (geographically oriented) input data. Depending on the user requirements, the system selects the best fitting model and available input information. Future research areas include organizing data management in the cereal grain supply chain, developing predictive models for other stakeholders (taking into account the period up to harvest), other Fusarium mycotoxins, and cereal grain types, and understanding the underlying effects of the regional component in the models
Zorgvuldige bestrijding van zeer besmettelijke dierziekten
Jong, M.C.M. de; Hagenaars, T.H.J. - \ 2010
In: Over zorgvuldige veehouderij. Veel instrumenten, één concert / Eijsackers, H., Scholten, M., Wageningen : Wageningen UR (Essaybundel 2010 ) - ISBN 9789085858959 - p. 64 - 75.
dierziekten - diergezondheid - ziektebestrijding - epidemieën - diergeneeskunde - veehouderij - vaccinatie - animal diseases - animal health - disease control - epidemics - veterinary science - livestock farming - vaccination
In dit hoofdstuk wordt de bestrijding besproken van uitbraken van zeer besmettelijke dierziekten, in het jargon 'aangifteplichtige ziekten' genoemd. Daarbij bediscussiëren de auteurs ook wat voor deze ziekten bestrijdingstechnisch mogelijk is. Of en hoe we dierziekten bestrijden, zijn maatschappelijke keuzes. Die keuzemogelijkheden worden beperkt door de technische mogelijkheden en vooral door de kennis over de effecten van de te nemen bestrijdingsmaatregelen.
Invasion of Phytophthora infestans at the landscape level; How do spatial scale and weather modulate the consequences of spatial heterogeneity in host resistance
Skelsey, P. ; Rossing, W.A.H. ; Kessel, G.J.T. ; Werf, W. van der - \ 2010
Phytopathology 100 (2010)11. - ISSN 0031-949X - p. 1146 - 1161.
potato late blight - gaussian plume model - spore dispersal - plant-disease - epidemics - spread - diversity - crop - severity - mixtures
Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with =1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions
Considering animals : moral convictions concerning animals and judgement on the culling of healthy animals in animal disease epidemics
Cohen, N.E. - \ 2010
Wageningen University. Promotor(en): Elsbeth Stassen, co-promotor(en): F.W.A. Brom; J.A. Stegeman. - [S.l. : S.n. - ISBN 9789085857952 - 194
dierziekten - epidemieën - uitselecteren - ziektebestrijding - attitudes - dierhouderij - samenleving - nederland - dierethiek - moraal - vonnis - animal diseases - epidemics - culling - disease control - animal husbandry - society - netherlands - animal ethics - moral - judgement
Varkensgriep en Mexicaanse griep
Loeffen, W.L.A. - \ 2009
Veehouder en Dierenarts 23 (2009)4. - ISSN 1381-8007 - p. 16 - 18.
varkensinfluenzavirussen - virusziekten - influenza - epidemieën - ziekten - swine influenza viruses - viral diseases - epidemics - diseases
In april 2009 werden in Californië (VS) twee kinderen ziek met wat later een nieuw type griepvirus (influenza) zou blijken te zijn. Influenzaachtige verschijnselen waren in de maand daarvoor al opvallend veel waargenomen in Mexico. Deze bleken te zijn veroorzaakt door hetzelfde type griepvirus. Al snel werd deze influenzavariant bekend onder de naam Mexicaanse griep
On the political economy of plant disease epidemics : Capita selecta in historical epidemiology door J.C. Zadoks
Franke, A.C. - \ 2009
Gewasbescherming 40 (2009)5. - ISSN 0166-6495 - p. 245 - 245.
epidemieën - epidemiologie - plantenziekten - ziektegeval-definities - diagnose - geschiedenis - gewasbescherming - epidemics - epidemiology - plant diseases - case definitions - diagnosis - history - plant protection
Dit boek brengt een aantal casussen bijeen waarin de invloed van epidemieën van plantenziekten op de mens en de maatschappij nader bestudeerd wordt. ‘Political economy’ refereert hier naar een term uit de achttiende eeuw die tegenwoordig vooral gebruikt wordt voor de studie van economische en politieke veranderingen met behulp van diverse, interdisciplinaire en vaak onconventionele benaderingen
Parameterization and evaluation of a spatiotemporal model of the potato late blight pathosystem
Skelsey, P. ; Kessel, G.J.T. ; Rossing, W.A.H. ; Werf, W. van der - \ 2009
Phytopathology 99 (2009)3. - ISSN 0031-949X - p. 290 - 300.
phytophthora-infestans - epidemics - disease - dispersal - netherlands - validation - simulation - strategies - resistance - sporangia
A spatiotemporal, integrodifference equation model of the potato late blight pathosystem is described. Formerly, the model was used in a theoretical context to analyze and predict epidemic dynamics in spatially heterogeneous mixtures of host genotypes. The model has now been modified to reflect a research interest in interactions between genotype, environment, landscape, and management. New parameter values describing host-pathogen interactions were determined and new environment-pathogen relationships included. A new analytical equation describing lesion expansion and associated necrosis has also been developed. These changes prompted a need to assess the quality of model predictions. Cultivar-isolate-specific interactions were characterized in the model using three quantitative components of resistance: infection efficiency, lesion growth rate, and sporulation intensity. These were measured on detached potato leaflets in the laboratory. Results of a sensitivity analysis illuminate the effect of different quantitative components of resistance and initial conditions on the shape of disease progress curves. Using the resistance components, the epidemic process of lesion expansion was separated from the epidemic process of lesion propagation providing two reference curves for diagnosing observed epidemics. The spatial component of the model was evaluated graphically in order to determine if realistic rates of focal expansion for potato late blight are produced. In accordance with theory, the radius of a predicted focus increased linearly with time and a constant focal velocity was reached that compared well with published experimental data. Validation data for the temporal model came from 20 late blight epidemics observed in field trials conducted in the Netherlands in 2002 and 2004. The field data and model were compared visually using disease progress curves, and numerically through a comparison of predicted and observed t(5) and t(50) points (time in days until 5 and 50% disease severity is reached, respectively) and relative areas under the disease progress curve values. Temporal model predictions were in close agreement with observational data and the ability of the model to translate measured resistance components, weather data, and initial conditions into realistic disease progress curves without the need for calibration confirms its utility as a tool in the analysis and diagnosis of epidemics.
Flexible decision-making in crisis events : discovering real options in the control of foot-and-mouth disease epidemics
Ge, L. - \ 2008
Wageningen University. Promotor(en): Ruud Huirne, co-promotor(en): A.R. Kristensen; Monique Mourits. - [S.l.] : S.n. - ISBN 9789085049692 - 149
crises - mond- en klauwzeer - epidemieën - besluitvorming - ziektebestrijding - markov-processen - onzekerheid - dynamisch programmeren - bayesiaanse theorie - dynamische modellen - bedrijfseconomie - beslissingsondersteunende systemen - beslissingsmodellen - foot and mouth disease - epidemics - decision making - disease control - markov processes - uncertainty - dynamic programming - bayesian theory - dynamic models - business economics - decision support systems - decision models

Keywords
Crisis event, foot-and-mouth disease (FMD), epidemic control, real options, decision flexibility, multi-level hierarchic Markov process (MLHMP), uncertainty, decision-support framework, turning moment, dynamic programming, Bayesian forecasting, dynamic models, overreacting, underreacting

This research introduced the real options way of thinking into decision-making in crisis events like animal epidemics, with foot-and-mouth disease (FMD) as a case in point. A unique angle was taken to investigate decision flexibility in choosing optimal control strategies. The main objective was to develop a flexible decision-support framework which corresponds to practice and provides consistent treatment of ongoing uncertainty in controlling animal epidemics. Conceptualisation and operationalisation of decision flexibility were the two main focuses.
A decision analysis revealed the dynamic and sequential nature of decision- making in the control of animal epidemics. The importance of decision flexibility was attributed to the existence of uncertainty and linked decisions in the multi-stage decision process. Timing of control options and the possibility of learning were found to be essential in conceptualising decision flexibility. To operationalise decision flexibility, the main methodological approach was the integration of multi-level hierarchic Markov process (MLHMP) and Bayesian forecasting methods. Based on MLHMP and dynamic generalised linear models (DGLM), a new decision-support framework was developed to investigate the impact of uncertainty and the possibility of learning in choosing the optimal timing of control options over time. The framework paid special attention to the interdependency among strategic, tactical, and operational decisions in managing FMD epidemics. The decision-support framework was shown to be useful in contingency planning for future epidemics.
Addressing the decision flexibility in a dynamic decision process, real options analysis and MLHMP were found to be complementary in developing the flexible decision-support framework. Both required dynamic assessment of future epidemic development and control options. Towards empirical application of the decision-support framework, an integrated epidemic-economic modelling approach was described and illustrated with simulated epidemics. It was shown that, by including decision flexibility in the dynamic decision process of epidemic control, the new modelling approach enabled more realistic estimation of the costs of underreacting or overreacting than the traditional static approaches.

Multi-scale modeling of potato late blight epidemics
Skelsey, P. - \ 2008
Wageningen University. Promotor(en): Bert Holtslag, co-promotor(en): Wopke van der Werf; Geert Jan Kessel; Walter Rossing. - S.l. : S.n. - ISBN 9789085049418 - 257
phytophthora infestans - solanum tuberosum - epidemieën - ziektemodellen - sporenverspreiding - virulentie - epidemiologie - geïntegreerde plagenbestrijding - gastheer-pathogeen interacties - epidemics - disease models - spore dispersal - virulence - epidemiology - integrated pest management - host pathogen interactions
Keywords: Solanum, invasion, Gaussian plume model, functional connectivity, landscape design

Proper landscape-scale deployment of disease resistant genotypes of agricultural crop species could
make those crops less vulnerable to invasion by resistance breaking genotypes. Here we develop a
multi-scale, spatio-temporal model of the potato late blight pathosystem (Phytophthora infestans -
Solanum tuberosum) to investigate spatial strategies for the deployment of host resistance. The
model comprises a landscape generator, a potato late blight model, and a suite of aerobiological
models, including an atmospheric dispersion model. Spatial phenomena are solved using Fast Fourier
transforms.
Increasing the number of host genotypes caused the greatest reduction in epidemic extent,
followed by reduction of the proportion of potato in the landscape, lowering the clustering of host
fields, and reducing the size of host fields. Simulation results showed that spatial spread through
short-distance “island hopping” is not a prerequisite for P. infestans invasions, and it appeared not
possible to generate host free zones at the landscape level that were large enough to provide
worthwhile levels of resilience against disease invasion from one host area to another. Deployment
of host resistance in genotype mixtures had a large effect on disease invasion. A new functional
connectivity parameter, characterizing the probability of successful infection following spore
dispersal, proved to be useful in interpreting these results.
Variation in simulation results revealed the importance of using an atmospheric dispersion
model for dispersal, with large weather data sets, and many random landscape iterations. The
specific coincidence in time and space between weather conditions and the geographic locations of
source and target sites defined true landscape connectivity and determined model results regarding
inoculum exchange between fields.
Given the apparent capacity of P. infestans for long distance transport of viable inoculum, it can
be concluded that spatial resistance deployment strategies that center on the creation of spatial
barriers to disease at scales up to several kilometers may not be effective in mitigating invasions of
virulent pathogen strains. Strategies that induce finer-grained spatial and genotypic heterogeneities
in host populations are more limiting to epidemic spread. Genotype mixing was an effective option
for generating agricultural landscapes that are comparatively resilient to disease invasion.
Epidemiological analysis of the 2006 bluetongue virus serotype 8 epidemic in north-western Europe, A risk map for epidemic potential in the Netherlands
Koeijer, A. de; Hartemink, N. ; Boender, G.J. ; Elbers, A.R.W. ; Hesterbeek, J.A.P. - \ 2007
niet bekend : EFSA - 18
bluetonguevirus - epidemieën - epidemiologie - risicoschatting - virusziekten - ziekten overgebracht door vectoren - ziekteoverdracht - nederland - noordwest-europa - bluetongue virus - epidemics - epidemiology - risk assessment - viral diseases - vector-borne diseases - disease transmission - netherlands - northwestern europe
One of the most important aspects of vector-borne infections is the strong influence of weather and climate on the transmission. In response to the major epidemic of bluetongue in north western Europe between summer and autumn 2006, an interest in BTV control issues developed. In this context, a map indicating the spatial variation in BTV risk in the north western European region would be very useful. To this end, a new approach is used in which they combine a mathematical epidemiological model and a geographical information system to obtain a spatially explicit measure for the risk of an outbreak of BTV when the virus is introduced in an area
Cost-effective control of a quarantine disease: a quantitative exploration using "design of experiments" methodology and bio-economic modeling
Breukers, M.L.H. ; Werf, W. van der; Kleijnen, J.P.C. ; Mourits, M.C.M. ; Oude Lansink, A.G.J.M. - \ 2007
Phytopathology 97 (2007)8. - ISSN 0031-949X - p. 945 - 957.
integrated pest-management - control strategies - transmission - epidemics
An integrated approach to control of quarantine diseases at the level of the plant production chain is complicated. The involved actors have different interests and the system is complex. Consequently, control policies may not be cost effective. By means of a bio-economic model for brown rot in the Dutch potato production chain, the efficacy of different control options was quantitatively analyzed. An impact analysis was performed using the methodology of ¿design of experiments¿ to quantify the effect of factors in interaction on incidence and costs of brown rot. Factors can be grouped as policy, sector, economic, and exogenous factors. Results show that brown rot incidence and economic consequences are determined predominantly by policy and sector factors and, to a lesser extent, by economic and exogenous factors. Scenario studies were performed to elucidate how the government and sector can optimize the cost-effectiveness of brown rot control. Optimal cost-effectiveness of control requires cooperation of the sector and government, in which case brown rot incidence can be reduced by 75% and the costs of control can be reduced by at least 2 million euros per year. This study demonstrates quantitatively the potential contribution of an integrated approach to cost-effective disease control at chain level.
Quantitative resistance and its components in 16 barley cultivars to yellow rust, Puccinia striiformis f.sp. hordei
Sandoval-Islas, J.S. ; Broers, L.H.M. ; Mora-Aguilera, G. ; Parlevliet, J.E. ; Osada-Kawasoe, S. ; Vivar, H.E. - \ 2007
Euphytica 153 (2007)3. - ISSN 0014-2336 - p. 295 - 308.
wheat leaf rust - adult-plant resistance - stripe rust - spring wheat - development stage - latent period - growth stages - epidemics
Sixteen barley cultivars with a susceptible infection type (IT = 7-8) in the seedling stage to an isolate of race 24 of Puccinia striiformis f. sp. hordei were planted at two locations in México. Disease severity (DS) parameters were assessed for the flag leaf and for the upper three leaves. The cultivars represented at least five levels of quantitative resistance ranging from very susceptible to quite resistant. ¿Granado¿, ¿Gloria/Copal¿ and ¿Calicuchima-92¿ represented the most resistant group and had an IT of 7 or 8. The cultivar × environment interaction variance, although significant, was very small compared with the cultivar variance. The disease severity parameters were highly correlated. The monocyclic parameter DSm, measured when the most susceptible cultivar had reached its maximum DS, was very highly correlated with the area under the disease progress curve (AUDPC), r being 0.98. Components of quantitative resistance were evaluated in two plant stages. In the seedling stage small cultivar effects for the latency period were observed, which were not correlated with the quantitative resistance measured in the field. In the adult plant stage the latency period (LP), infection frequency (IF) and colonization rate (CR) were measured in the upper two leaves. The LP was much longer than in the seedling stage and differed strongly between cultivars. The differences in IF were too large, those in CR varied much less. The components showed association with one another. The LP and IF were well correlated with the AUDPC (r = 0.7-0.8).
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