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Estimates for local and movement-based transmission of bovine tuberculosis in British cattle.

Green DM, Kiss IZ, Mitchell AP, Kao RR - Proc. Biol. Sci. (2008)

Bottom Line: The herds identified as high risk in 2004 by our model are in broad agreement with those officially designated as such at that time.However, border areas at the edges of high-risk regions are different, suggesting possible areas that should be targeted to prevent further geographical spread of disease.With these areas expanding rapidly over the last decade, their close surveillance is important to both identify infected herds qucikly, and limit their further growth.

View Article: PubMed Central - PubMed

Affiliation: Institute of Aquaculture, University of Stirling, Stirling, Stirlingshire, UK.

ABSTRACT
Both badgers and livestock movements have been implicated in contributing to the ongoing epidemic of bovine tuberculosis (BTB) in British cattle. However, the relative contributions of these and other causes are not well quantified. We used cattle movement data to construct an individual (premises)-based model of BTB spread within Great Britain, accounting for spread due to recorded cattle movements and other causes. Outbreak data for 2004 were best explained by a model attributing 16% of herd infections directly to cattle movements, and a further 9% unexplained, potentially including spread from unrecorded movements. The best-fit model assumed low levels of cattle-to-cattle transmission. The remaining 75% of infection was attributed to local effects within specific high-risk areas. Annual and biennial testing is mandatory for herds deemed at high risk of infection, as is pre-movement testing from such herds. The herds identified as high risk in 2004 by our model are in broad agreement with those officially designated as such at that time. However, border areas at the edges of high-risk regions are different, suggesting possible areas that should be targeted to prevent further geographical spread of disease. With these areas expanding rapidly over the last decade, their close surveillance is important to both identify infected herds qucikly, and limit their further growth.

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Related in: MedlinePlus

CIs. Estimates and 95% profile CIs for proportions of infections caused by movement, background and high-risk area transmission. Model likelihood was evaluated at the end of 2004 for (a) the high within-herd and (b) low within-herd transmission models.
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fig1: CIs. Estimates and 95% profile CIs for proportions of infections caused by movement, background and high-risk area transmission. Model likelihood was evaluated at the end of 2004 for (a) the high within-herd and (b) low within-herd transmission models.

Mentions: The proportions of infections due to movements, background rate spread, and presence in high-risk areas, and with corresponding transmission rates μ, β, γ and radius r are shown in table 1 and figure 1 (and figure A1 in the electronic supplementary material) for different modelling assumptions, using the year 2003 for model seeding, and the year 2004 for evaluation of the model likelihood function (given in the electronic supplementary material). Parameter w, the assumed possible window of infection prior to discovery was set at 1 year, requiring a model start date at the beginning of 2002. Models were fit using a maximum-likelihood method and compared via the Akaike information criterion (AIC; Akaike 1974). Where models were nested (high within-herd versus low within-herd, background versus no background), statistical significance was confirmed using likelihood ratio tests. The best-fit model assumed high-risk areas based on radii surrounding index cases, and low within-herd transmission, where only cattle that have stayed on premises in high-risk areas are assumed potentially infectious. Movement accounted for 16% of infections, with background infection 9%, and the remaining 75%, due to high-risk area transmission. The 95% CIs are narrow with confidence in the proportion of movement-related infections notably strong (figure 1). Model results were insensitive to the model start date and the infection window w (duration of infectiousness before reported breakdown) within the range of 70–365 days (figure A1 in the electronic supplementary material) due to repeated sampling from the high-risk areas (figure A2 in the electronic supplementary material).


Estimates for local and movement-based transmission of bovine tuberculosis in British cattle.

Green DM, Kiss IZ, Mitchell AP, Kao RR - Proc. Biol. Sci. (2008)

CIs. Estimates and 95% profile CIs for proportions of infections caused by movement, background and high-risk area transmission. Model likelihood was evaluated at the end of 2004 for (a) the high within-herd and (b) low within-herd transmission models.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2366193&req=5

fig1: CIs. Estimates and 95% profile CIs for proportions of infections caused by movement, background and high-risk area transmission. Model likelihood was evaluated at the end of 2004 for (a) the high within-herd and (b) low within-herd transmission models.
Mentions: The proportions of infections due to movements, background rate spread, and presence in high-risk areas, and with corresponding transmission rates μ, β, γ and radius r are shown in table 1 and figure 1 (and figure A1 in the electronic supplementary material) for different modelling assumptions, using the year 2003 for model seeding, and the year 2004 for evaluation of the model likelihood function (given in the electronic supplementary material). Parameter w, the assumed possible window of infection prior to discovery was set at 1 year, requiring a model start date at the beginning of 2002. Models were fit using a maximum-likelihood method and compared via the Akaike information criterion (AIC; Akaike 1974). Where models were nested (high within-herd versus low within-herd, background versus no background), statistical significance was confirmed using likelihood ratio tests. The best-fit model assumed high-risk areas based on radii surrounding index cases, and low within-herd transmission, where only cattle that have stayed on premises in high-risk areas are assumed potentially infectious. Movement accounted for 16% of infections, with background infection 9%, and the remaining 75%, due to high-risk area transmission. The 95% CIs are narrow with confidence in the proportion of movement-related infections notably strong (figure 1). Model results were insensitive to the model start date and the infection window w (duration of infectiousness before reported breakdown) within the range of 70–365 days (figure A1 in the electronic supplementary material) due to repeated sampling from the high-risk areas (figure A2 in the electronic supplementary material).

Bottom Line: The herds identified as high risk in 2004 by our model are in broad agreement with those officially designated as such at that time.However, border areas at the edges of high-risk regions are different, suggesting possible areas that should be targeted to prevent further geographical spread of disease.With these areas expanding rapidly over the last decade, their close surveillance is important to both identify infected herds qucikly, and limit their further growth.

View Article: PubMed Central - PubMed

Affiliation: Institute of Aquaculture, University of Stirling, Stirling, Stirlingshire, UK.

ABSTRACT
Both badgers and livestock movements have been implicated in contributing to the ongoing epidemic of bovine tuberculosis (BTB) in British cattle. However, the relative contributions of these and other causes are not well quantified. We used cattle movement data to construct an individual (premises)-based model of BTB spread within Great Britain, accounting for spread due to recorded cattle movements and other causes. Outbreak data for 2004 were best explained by a model attributing 16% of herd infections directly to cattle movements, and a further 9% unexplained, potentially including spread from unrecorded movements. The best-fit model assumed low levels of cattle-to-cattle transmission. The remaining 75% of infection was attributed to local effects within specific high-risk areas. Annual and biennial testing is mandatory for herds deemed at high risk of infection, as is pre-movement testing from such herds. The herds identified as high risk in 2004 by our model are in broad agreement with those officially designated as such at that time. However, border areas at the edges of high-risk regions are different, suggesting possible areas that should be targeted to prevent further geographical spread of disease. With these areas expanding rapidly over the last decade, their close surveillance is important to both identify infected herds qucikly, and limit their further growth.

Show MeSH
Related in: MedlinePlus