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Escherichia coli O157 infection on Scottish cattle farms: dynamics and control.

Zhang XS, Woolhouse ME - J R Soc Interface (2010)

Bottom Line: We first generate distributions of model parameter estimates using Markov chain Monte Carlo methods.Despite considerable uncertainty in parameter values, each set of parameter values within the 95th percentile range implies a fairly similar impact of interventions.Targeted interventions based on farm-level risk factors are more efficient than non-targeted interventions.

View Article: PubMed Central - PubMed

Affiliation: Centre for Infectious Diseases, University of Edinburgh, , Kings Buildings, West Mains Road, Edinburgh EH9 3JT, UK. xu-sheng.zhang@hpa.org.uk

ABSTRACT
In this study, we parametrize a stochastic individual-based model of the transmission dynamics of Escherichia coli O157 infection among Scottish cattle farms and use the model to predict the impacts of both targeted and non-targeted interventions. We first generate distributions of model parameter estimates using Markov chain Monte Carlo methods. Despite considerable uncertainty in parameter values, each set of parameter values within the 95th percentile range implies a fairly similar impact of interventions. Interventions that reduce the transmission coefficient and/or increase the recovery rate of infected farms (e.g. via vaccination and biosecurity) are much more effective in reducing the level of infection than reducing cattle movement rates, which improves effectiveness only when the overall control effort is small. Targeted interventions based on farm-level risk factors are more efficient than non-targeted interventions. Herd size is a major determinant of risk of infection, and our simulations confirmed that targeting interventions at farms with the largest herds is almost as effective as targeting based on overall risk. However, because of the striking characteristic that the infection force depends weakly on the number of infected farms, no interventions that are less than 100 per cent effective can eradicate E. coli O157 infection from Scottish cattle farms, implying that eliminating the disease is impractical.

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Related in: MedlinePlus

Effectiveness of non-targeted interventions. Five different interventions are displayed: no movement-related transmission, reducing transmission coefficient, reducing infectious period (i.e. increasing recovery rate), reducing transmission coefficient and infectious period simultaneously and combining all three. The prevalence was obtained after interventions have been performed for 9 years (figure 3). The mean values were obtained by averaging over the last 3 years across 2486 sets of original model parameter values from the converged MCMC process. Error bars denote standard deviations. Dashed orange line, no movements; dashed pink line, reduce β; dashed dark blue line, increase γ; dashed green line, joint control with movements; dashed light blue line, joint control without movement.
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RSIF20100470F4: Effectiveness of non-targeted interventions. Five different interventions are displayed: no movement-related transmission, reducing transmission coefficient, reducing infectious period (i.e. increasing recovery rate), reducing transmission coefficient and infectious period simultaneously and combining all three. The prevalence was obtained after interventions have been performed for 9 years (figure 3). The mean values were obtained by averaging over the last 3 years across 2486 sets of original model parameter values from the converged MCMC process. Error bars denote standard deviations. Dashed orange line, no movements; dashed pink line, reduce β; dashed dark blue line, increase γ; dashed green line, joint control with movements; dashed light blue line, joint control without movement.

Mentions: The simulation results for the various non-targeted interventions are shown in figure 4. It is clearly shown that reducing cattle movement between farms is least effective and shortening the infectious period (i.e. enlarging the recovery rate) is most effective in controlling E. coli O157 infection on Scottish cattle farms. The difference between shortening the infectious period and reducing the transmission coefficient is not substantial: for example, with the same control effort c =50 per cent, the prevalence decreases from 16 per cent to about 7 and 8 per cent respectively. Interventions that reduce both the transmission coefficient and the recovery rate result in a greater reduction in the prevalence of E. coli O157 infection. Additionally eliminating movement-related transmission significantly increases the effectiveness of the control only when the control effort is small.Figure 4.


Escherichia coli O157 infection on Scottish cattle farms: dynamics and control.

Zhang XS, Woolhouse ME - J R Soc Interface (2010)

Effectiveness of non-targeted interventions. Five different interventions are displayed: no movement-related transmission, reducing transmission coefficient, reducing infectious period (i.e. increasing recovery rate), reducing transmission coefficient and infectious period simultaneously and combining all three. The prevalence was obtained after interventions have been performed for 9 years (figure 3). The mean values were obtained by averaging over the last 3 years across 2486 sets of original model parameter values from the converged MCMC process. Error bars denote standard deviations. Dashed orange line, no movements; dashed pink line, reduce β; dashed dark blue line, increase γ; dashed green line, joint control with movements; dashed light blue line, joint control without movement.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104328&req=5

RSIF20100470F4: Effectiveness of non-targeted interventions. Five different interventions are displayed: no movement-related transmission, reducing transmission coefficient, reducing infectious period (i.e. increasing recovery rate), reducing transmission coefficient and infectious period simultaneously and combining all three. The prevalence was obtained after interventions have been performed for 9 years (figure 3). The mean values were obtained by averaging over the last 3 years across 2486 sets of original model parameter values from the converged MCMC process. Error bars denote standard deviations. Dashed orange line, no movements; dashed pink line, reduce β; dashed dark blue line, increase γ; dashed green line, joint control with movements; dashed light blue line, joint control without movement.
Mentions: The simulation results for the various non-targeted interventions are shown in figure 4. It is clearly shown that reducing cattle movement between farms is least effective and shortening the infectious period (i.e. enlarging the recovery rate) is most effective in controlling E. coli O157 infection on Scottish cattle farms. The difference between shortening the infectious period and reducing the transmission coefficient is not substantial: for example, with the same control effort c =50 per cent, the prevalence decreases from 16 per cent to about 7 and 8 per cent respectively. Interventions that reduce both the transmission coefficient and the recovery rate result in a greater reduction in the prevalence of E. coli O157 infection. Additionally eliminating movement-related transmission significantly increases the effectiveness of the control only when the control effort is small.Figure 4.

Bottom Line: We first generate distributions of model parameter estimates using Markov chain Monte Carlo methods.Despite considerable uncertainty in parameter values, each set of parameter values within the 95th percentile range implies a fairly similar impact of interventions.Targeted interventions based on farm-level risk factors are more efficient than non-targeted interventions.

View Article: PubMed Central - PubMed

Affiliation: Centre for Infectious Diseases, University of Edinburgh, , Kings Buildings, West Mains Road, Edinburgh EH9 3JT, UK. xu-sheng.zhang@hpa.org.uk

ABSTRACT
In this study, we parametrize a stochastic individual-based model of the transmission dynamics of Escherichia coli O157 infection among Scottish cattle farms and use the model to predict the impacts of both targeted and non-targeted interventions. We first generate distributions of model parameter estimates using Markov chain Monte Carlo methods. Despite considerable uncertainty in parameter values, each set of parameter values within the 95th percentile range implies a fairly similar impact of interventions. Interventions that reduce the transmission coefficient and/or increase the recovery rate of infected farms (e.g. via vaccination and biosecurity) are much more effective in reducing the level of infection than reducing cattle movement rates, which improves effectiveness only when the overall control effort is small. Targeted interventions based on farm-level risk factors are more efficient than non-targeted interventions. Herd size is a major determinant of risk of infection, and our simulations confirmed that targeting interventions at farms with the largest herds is almost as effective as targeting based on overall risk. However, because of the striking characteristic that the infection force depends weakly on the number of infected farms, no interventions that are less than 100 per cent effective can eradicate E. coli O157 infection from Scottish cattle farms, implying that eliminating the disease is impractical.

Show MeSH
Related in: MedlinePlus