The role of mathematical modelling in understanding the epidemiology and control of sheep transmissible spongiform encephalopathies: a review

Gubbins, Simon; Touzeau, Suzanne; Hagenaars, T.H.J.

doi:10.1051/vetres/2010014

Cited by 7 publications

(7 citation statements)

References 76 publications

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“…For a field study showing the success of selective breeding to control CS at the flock level see Nodelijk et al (2011). Mathematical modelling studies have been applied to data of within-flock outbreaks and of data at national-flock level, yielding a range of epidemiological insights (for a review see Gubbins et al (2010)). Concerning within-flock outbreaks, some of the insights might be outbreak specific.…”

Section: Epidemiologymentioning

confidence: 99%

“…In addition, it is important to note that the sheep population in a MS, or of a certain breed in a MS, is structured in flocks, and contacts between sheep residing within the same flock will be more intensive than that between animals residing in different flocks. This means that it is natural to consider two levels of transmission in the population: within-flock and between-flock transmission (Gubbins et al, 2010). From this point of view, a situation with R 0 <1 for CS may be interpreted as a situation in which isolated within-flock outbreaks of CS may occur but no major between-flock spread will be possible.…”

Section: The Concept Of 'Fading-out'mentioning

confidence: 99%

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Scientific Opinion on the scrapie situation in the EU after 10 years of monitoring and control in sheep and goats

Hald

Baggesen

2014

EFSA Journal

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To assess the effectiveness of the strategies implemented in the European Union (EU) to control Classical scrapie (CS), epidemiological data have been compared in the context of the efforts in terms of control measures applied over time. Official EU surveillance data and results from questionnaire surveys of EU Member States (MSs) have been used along with case studies. A spatio-temporal description of the occurrence of small ruminants TSEs in MSs in the period 2002-2012 is provided, with a particular focus on CS in sheep. Based on information collected from MSs, the potential effectiveness of breeding programmes for resistance to CS (BP-CS) in the dissemination of resistance into the general sheep population has been assessed for those countries for which the CS trend analysis has been performed. CS in sheep was reported in 17 MSs (average prevalence: 8.7 cases/10 000 tests), with heterogeneous trends and geographical distribution: among the 13 countries reporting a consistent number of cases, the trend analysis shows a statistically significant decreasing trend only for six of them. Variations in the implementation of genetic and non-genetic measures for the control of CS may explain the failure to improve the disease situation in the remaining seven MSs. At a national level, a reduction in CS seems to be linked to better-achieving BP-CSs. Control options applied to CS in sheep and goats indicate that a CS eradication policy that relies solely on the detection of infected flocks by post-mortem testing and subsequent depopulation would be unlikely to succeed. A minimum frequency of the ARR allele in a sheep population above which CS may be expected to fade-out could be estimated for each specific national sheep population. Recommendations for additional/alternative measures to control CS in sheep and goats are formulated. Scrapie situation in the EU EFSA Journal 2014;12 (7):3781 2 SUMMARYFollowing a request from the European Commission (EC), the EFSA Panel on Biological Hazards (BIOHAZ) was asked to deliver a scientific opinion on the scrapie situation in the European Union (EU) after 10 years of monitoring and control in sheep and goats. In particular, in order to evaluate the measures in place and assess the progress accomplished, the EC consulted EFSA to gain a better understanding of the dynamics of the epidemiological situation of Classical scrapie (CS) and Atypical scrapie (AS), and a retrospective analysis of the effectiveness of the control tools encompassed by EU legislation.The opinion provides background information in relation to CS and AS in sheep and goats, including information on the nature of the agents, genetic susceptibility of the hosts, transmission pathways and epidemiology of the diseases.Based on information from the EU TSE surveillance database, CS and AS in sheep and goats in the period 2002-2012 have been analysed to provide a spatio-temporal description of the occurrence of the diseases, after appropriate statistical adjustment accounting for the main known confounding factor...

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Section: Epidemiologymentioning

confidence: 99%

Section: The Concept Of 'Fading-out'mentioning

confidence: 99%

Scientific Opinion on the scrapie situation in the EU after 10 years of monitoring and control in sheep and goats

Hald

Baggesen

2014

EFSA Journal

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“…We model the Dutch national sheep population as a population of sheep flocks that vary in genetic content, distinguishing two levels of transmission: within a flock and between flocks. For a review of previous within-flock and between-flock scrapie transmission modelling see [ 16 ]. The importance of taking into account the genetic variation between flocks can be illustrated as follows.…”

Section: Methodsmentioning

confidence: 99%

Modelling of strategies for genetic control of scrapie in sheep: The importance of population structure

Hagenaars¹,

Melchior²,

Windig³

et al. 2018

PLoS ONE

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Scrapie is a transmissible spongiform encephalopathy in sheep and an example of a disease that may be controlled through breeding for disease resistance. Member states of the European Union have introduced strategies for breeding against scrapie based on the selection of genetically resistant breeding rams. An ambitious strategy adopted in The Netherlands consisted of selecting resistant rams for breeding throughout both breeding and production sectors. Mathematical modelling of the effect of a breeding program on the spreading capacity of scrapie in a national flock is needed for making assessments on how long a breeding strategy needs to be maintained to achieve disease control. Here we describe such a model applied to the Dutch situation, with the use of data on the genetic content of the Dutch sheep population as well as on scrapie occurrence in this population. We show that the time needed for obtaining scrapie control depends crucially on two parameters measuring sheep population structure: the between-flock heterogeneity in genotype frequencies, and the heterogeneity of mixing (contact rates) between sheep flocks. Estimating the first parameter from Dutch genetic survey data and assuming scenario values for the second one, enables model prediction of the time needed to achieve scrapie control in The Netherlands.

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“…Those publications were typically dealing with individual outbreaks for which more detailed data was available, and were reviewed in Ref. [ 12 ]. The mathematical structure of the models of most previous work (including Refs.…”

Section: Methodsmentioning

confidence: 99%

“…Some member states have introduced a wider national breeding programme than requested by the EU, including The Netherlands (started in 1998), Great Britain (started in 2001) [ 7 – 11 ], and France (started in 2002). As these programs have to be run over many years there is a need for reliable model projections of their expected future effects [ 12 ]. In such predictive model analyses it is often desirable to quantify within-flock scrapie transmission as a function of flock genotype profile.…”

Section: Introductionmentioning

confidence: 99%

Investigation of a Simple Model for Within-Flock Transmission of Scrapie

Hagenaars

Windig

2015

PLoS ONE

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Genetic control programs for scrapie in sheep build on solid knowledge of how susceptibility to scrapie is modulated by the prion protein genotype at the level of an individual sheep. In order to satisfactorily analyze the effectivity of control programs at the population level, insight is needed at the flock level, i.e., how the grouping of sheep in flocks affects the population-level transmission risk. In particular, one would like to understand how this risk is affected by between-flock differences in genotype frequency distribution. A first step is to model the scrapie transmission risk within a flock as a function of the flock genotype profile. Here we do so by estimating parameters for a model of within-flock transmission using genotyping data on Dutch flocks affected by scrapie. We show that the data are consistent with a relatively simple transmission model assuming horizontal transmission and homogeneous mixing between animals. The model expresses the basic reproduction number for within-flock scrapie as a weighted average of genotype-specific susceptibilities, multiplied by a single overall transmission parameter. The value of the overall transmission parameter may vary between flocks to account for random between-flock variation in non-genetic determinants such as management practice. Here we provide an estimate of its mean value and variation for Dutch flocks.

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The role of mathematical modelling in understanding the epidemiology and control of sheep transmissible spongiform encephalopathies: a review

Cited by 7 publications

References 76 publications

Scientific Opinion on the scrapie situation in the EU after 10 years of monitoring and control in sheep and goats

Scientific Opinion on the scrapie situation in the EU after 10 years of monitoring and control in sheep and goats

Modelling of strategies for genetic control of scrapie in sheep: The importance of population structure

Investigation of a Simple Model for Within-Flock Transmission of Scrapie

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