bTB Breakdowns Research Articles

Herd-level risk factors of bovine tuberculosis in England and Wales after the 2001 foot-and-mouth disease epidemic

We present the results of a 2005 case-control study of bovine tuberculosis (bTB) breakdowns in English and Welsh herds. The herd management, farming practices, and environmental factors of 401 matched pairs of case and control herds were investigated to provide a picture of herd-level risk factors in areas of varying bTB incidence. A global conditional logistic regression model, with region-specific variants, was used to compare case herds that had experienced a confirmed bTB breakdown to contemporaneous control herds matched on region, herd type, herd size, and parish testing interval. Contacts with cattle from contiguous herds and sourcing cattle from herds with a recent history of bTB were associated with an increased risk in both the global and regional analyses. Operating a farm over several premises, providing cattle feed inside the housing, and the presence of badgers were also identified as significantly associated with an increased bTB risk. Steps taken to minimize cattle contacts with neighboring herds and altering trading practices could have the potential to reduce the size of the bTB epidemic. In principle, limiting the interactions between cattle and wildlife may also be useful; however this study did not highlight any specific measures to implement.

Local Cattle and Badger Populations Affect the Risk of Confirmed Tuberculosis in British Cattle Herds

BackgroundThe control of bovine tuberculosis (bTB) remains a priority on the public health agenda in Great Britain, after launching in 1998 the Randomised Badger Culling Trial (RBCT) to evaluate the effectiveness of badger (Meles meles) culling as a control strategy. Our study complements previous analyses of the RBCT data (focusing on treatment effects) by presenting analyses of herd-level risks factors associated with the probability of a confirmed bTB breakdown in herds within each treatment: repeated widespread proactive culling, localized reactive culling and no culling (survey-only).Methodology/Principal FindingsNew cases of bTB breakdowns were monitored inside the RBCT areas from the end of the first proactive badger cull to one year after the last proactive cull. The risk of a herd bTB breakdown was modeled using logistic regression and proportional hazard models adjusting for local farm-level risk factors. Inside survey-only and reactive areas, increased numbers of active badger setts and cattle herds within 1500 m of a farm were associated with an increased bTB risk. Inside proactive areas, the number of M. bovis positive badgers initially culled within 1500 m of a farm was the strongest predictor of the risk of a confirmed bTB breakdown.Conclusions/SignificanceThe use of herd-based models provide insights into how local cattle and badger populations affect the bTB breakdown risks of individual cattle herds in the absence of and in the presence of badger culling. These measures of local bTB risks could be integrated into a risk-based herd testing programme to improve the targeting of interventions aimed at reducing the risks of bTB transmission.

Husbandry practices, badger sett density and habitat composition as risk factors for transient and persistent bovine tuberculosis on UK cattle farms

Bovine tuberculosis (bTB) is a persistent problem in cattle herds in Great Britain and Ireland. Farm management and cattle husbandry practices can influence the risk of transmission of bTB and hence the likelihood of bTB breakdown (≥1 reactor to the tuberculin skin test). Biological differences are expected in the transmission dynamics, and hence risk factors for bTB breakdown, on farms where infection persists in the herd compared to farms where infection is more sporadic or short-lived. Comparative case–control studies were performed to test farm management practices as potential risk factors for transient (under breakdown restrictions for ≤6 months) and persistent (under breakdown restrictions for >6 months) bTB breakdown over 5 years (1995–1999) on 179 and 171 UK cattle farms, respectively. Farms were characterised for badger sett density and farm habitat composition by ground survey, farmers were questioned retrospectively on management practices, and cases and controls were identified from national tuberculin test records. Controlling for routine tuberculin testing interval, log-transformed herd size, regional location, badger sett density and farm habitat complexity, multivariable logistic regression identified increased odds of both transient and persistent breakdown on farms that bought-in cows (odds ratio (OR) ≥ 4.9; 95% confidence interval (CI) ≥ 1.1;22.8). In addition, the purchase of >50 head of cattle (OR = 4.0, 95% CI = 1.0;16.0) and the storage of manure for ≥6 months (OR = 4.4; 95% CI = 1.3;15.4) were risk factors for transient breakdown, whereas the use of silage clamps (OR = 9.1; 95% CI = 2.0;40.8) increased the risk of persistent breakdown. Decreased odds of both transient and persistent breakdown were associated with higher stocking densities (>3 cattle/ha) (OR ≤ 0.2; 95% CI ≤ 0.1;0.9), and running mixed herd enterprises compared to only beef or dairy (OR = 0.1; 95% CI = 0.0;0.7) was an additional protective factor against persistent breakdown. In these analyses, the covariates log herd size and tuberculin testing interval were significant predictors of both transient and persistent breakdown, whereas active badger sett density and regional location only affected the risk of persistent breakdown. The collective results suggest that the probability of transient breakdown is most strongly influenced by the purchase of cattle over other management variables and covariates, whereas the probability of persistent breakdown appears to be mostly affected by management factors relating to type of herd enterprise and silage storage in addition to the relative density of badgers. Implications for bTB management are discussed.

Bovine tuberculosis in cattle: reduced risk on wildlife-friendly farms

The associations between habitat and other factors that lead to the risk of bovine tuberculosis (bTB) in diary cattle were examined in an unmatched case-control study. Data from 60 herds with recent history of bTB and 60 controls were analysed using logistic regression. The predictors included farmland habitat, topography, indices of badger density and herd size. Information-theoretic approaches were used to identify those predictor variables explaining the greatest variation in cattle herd bTB breakdowns. Reduced risk of bTB was associated with the management of farmland in ways favourable to wildlife conservation, as encouraged by recent (2005) European Common Agricultural Policy reforms.