Predicting prolonged bovine tuberculosis breakdowns in Great Britain as an aid to control

Karolemeas, Katerina; McKinley, Trevelyan J.; Clifton-Hadley, R. S.; Goodchild, Tony; Mitchell, A.; Johnston, W. Thomas; Conlan, Andrew J. K.; Donnelly, Christl A.; Wood, James

doi:10.1016/j.prevetmed.2010.09.007

Cited by 35 publications

(51 citation statements)

References 17 publications

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“…These empirical relationships are consistent with previous analyses suggesting that confirmation is associated with an increase in the duration of breakdowns [25], but has negligible impact on recurrence [10]. In contrast to the consistency of the duration of breakdowns across all areas there is a marked increase in the rate of recurrence with local risk as measured by PTI.…”

Section: Resultssupporting

confidence: 90%

“…The persistence of bTB has previously been demonstrated to scale with herd size [27]; a known risk factor for both prolongation [25] of breakdowns in GB and recurrence in Irish herds [28]. We extend these analyses to quantify the relationship of our two persistence measures with herd size.…”

Section: Resultsmentioning

confidence: 85%

“…We therefore quantify within-herd persistence through two competing measures related to the duration and the rate of recurrence of breakdowns. The duration of breakdowns is captured by the probability that breakdowns are prolonged [25], defined as lasting longer than 240 days. Recurrence is captured through the probability of a breakdown recurring [10] within a fixed time horizon of 6, 12 and 24 months after the end of a breakdown.…”

Section: Resultsmentioning

confidence: 99%

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Estimating the Hidden Burden of Bovine Tuberculosis in Great Britain

et al. 2012

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The number of cattle herds placed under movement restrictions in Great Britain (GB) due to the suspected presence of bovine tuberculosis (bTB) has progressively increased over the past 25 years despite an intensive and costly test-and-slaughter control program. Around 38% of herds that clear movement restrictions experience a recurrent incident (breakdown) within 24 months, suggesting that infection may be persisting within herds. Reactivity to tuberculin, the basis of diagnostic testing, is dependent on the time from infection. Thus, testing efficiency varies between outbreaks, depending on weight of transmission and cannot be directly estimated. In this paper, we use Approximate Bayesian Computation (ABC) to parameterize two within-herd transmission models within a rigorous inferential framework. Previous within-herd models of bTB have relied on ad-hoc methods of parameterization and used a single model structure (SORI) where animals are assumed to become detectable by testing before they become infectious. We study such a conventional within-herd model of bTB and an alternative model, motivated by recent animal challenge studies, where there is no period of epidemiological latency before animals become infectious (SOR). Under both models we estimate that cattle-to-cattle transmission rates are non-linearly density dependent. The basic reproductive ratio for our conventional within-herd model, estimated for scenarios with no statutory controls, increases from 1.5 (0.26–4.9; 95% CI) in a herd of 30 cattle up to 4.9 (0.99–14.0) in a herd of 400. Under this model we estimate that 50% (33–67) of recurrent breakdowns in Britain can be attributed to infection missed by tuberculin testing. However this figure falls to 24% (11–42) of recurrent breakdowns under our alternative model. Under both models the estimated extrinsic force of infection increases with the burden of missed infection. Hence, improved herd-level testing is unlikely to reduce recurrence unless this extrinsic infectious pressure is simultaneously addressed.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

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Estimating the Hidden Burden of Bovine Tuberculosis in Great Britain

et al. 2012

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“…The Irish study above contrasts with a recent GB study, which showed that ~30% of herd breakdowns extend for >8 months [43] and consume disproportional resources as well as acting as ongoing sources of infection. Breakdown duration was a function of infection status and test performance.…”

Section: Other Epidemiological Studiesmentioning

confidence: 74%

Herd-Level Risk Factors for Bovine Tuberculosis: A Literature Review

Skuce

Allen

McDowell

2012

Veterinary Medicine International

147

145

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Bovine tuberculosis (TB), caused by Mycobacterium bovis, is one of the most challenging endemic diseases currently facing government, the veterinary profession, and the farming industry in the United Kingdom and Ireland and in several other countries. The disease has a notoriously complex epidemiology; the scientific evidence supports both cattle-cattle and wildlife-cattle transmission routes. To produce more effective ways of reducing such transmission, it is important to understand those risk factors which influence the presence or absence of bovine TB in cattle herds. Here we review the literature on herd-level risk factor studies. Whilst risk factors operate at different scales and may vary across regions, epidemiological studies have identified a number of risk factors associated with bovine TB herd breakdowns, including the purchase of cattle, the occurrence of bovine TB in contiguous herds, and/or the surrounding area as well as herd size. Other factors identified in some studies include farm and herd management practices, such as, the spreading of slurry, the use of certain housing types, farms having multiple premises, and the use of silage clamps. In general, the most consistently identified risk factors are biologically plausible and consistent with known transmission routes involving cattle-cattle and wildlife-cattle pathways.

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“…Many studies have found differences in BTB risk between dairy and beef cattle [29-31], and indeed the unadjusted age profiles of beef and dairy reactor numbers are hugely different (Figure 1b). However, we found that when reactor numbers are normalised by test patterns the age dependencies are remarkably comparable.…”

Section: Discussionmentioning

confidence: 99%

Age-dependent patterns of bovine tuberculosis in cattle

Brooks-Pollock

Conlan

Mitchell

et al. 2013

Vet Res

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Bovine tuberculosis (BTB) is an important livestock disease, seriously impacting cattle industries in both industrialised and pre-industrialised countries. Like TB in other mammals, infection is life long and, if undiagnosed, may progress to disease years after exposure. The risk of disease in humans is highly age-dependent, however in cattle, age-dependent risks have yet to be quantified, largely due to insufficient data and limited diagnostics. Here, we estimate age-specific reactor rates in Great Britain by combining herd-level testing data with spatial movement data from the Cattle Tracing System (CTS). Using a catalytic model, we find strong age dependencies in infection risk and that the probability of detecting infection increases with age. Between 2004 and 2009, infection incidence in cattle fluctuated around 1%. Age-specific incidence increased monotonically until 24–36 months, with cattle aged between 12 and 36 months experiencing the highest rates of infection. Beef and dairy cattle under 24 months experienced similar infection risks, however major differences occurred in older ages. The average reproductive number in cattle was greater than 1 for the years 2004–2009. These methods reveal a consistent pattern of BTB rates with age, across different population structures and testing patterns. The results provide practical insights into BTB epidemiology and control, suggesting that targeting a mass control programme at cattle between 12 and 36 months could be beneficial.

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Predicting prolonged bovine tuberculosis breakdowns in Great Britain as an aid to control

Cited by 35 publications

References 17 publications

Estimating the Hidden Burden of Bovine Tuberculosis in Great Britain

Estimating the Hidden Burden of Bovine Tuberculosis in Great Britain

Herd-Level Risk Factors for Bovine Tuberculosis: A Literature Review

Age-dependent patterns of bovine tuberculosis in cattle

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