Coupling models of cattle and farms with models of badgers for predicting the dynamics of bovine tuberculosis (TB) (original) (raw)
Related papers
Ecological Modelling, 2003
We describe an individual-based spatially-explicit model designed to investigate the dynamics of badger populations and TB epidemiology in a real landscape. We develop a methodology for evaluating the sensitivity of the model to its input parameters through the use of power analysis, partial correlation coefficients and binary logistic regression. This novel approach to sensitivity analysis provides a formal statement of confidence in our findings based on statistical power, and a solution for analysing sparse data sets of disease prevalence. The sensitivity analysis revealed that the simulated badger population size after 20 years was most dependent on five parameters affecting female recruitment (probability of breeding, mortality of adult females in the first half of the year, mortality of juvenile females in the second half of the year and mortality of female cubs in the both halves of the year). The simulated prevalence of TB was most affected by the population size, the rate at which infectious badgers transmit the disease to other members of their social group, and the rate at which the disease is spread outside of the social group.
Title Spatio-Temporal Modelling of TB in Cattle Herds
We examine spatial association of bovine TB in cattle herds using data from Ireland. Badgers (Meles meles), a protected species under the Wildlife Act 1976 (OAG 2012), have been implicated in the spread of the disease in cattle. Current disease control policies include reactive culling (in response to TB outbreaks) of badgers in the index and neighbouring farms. Kelly and More (2011) using generalized linear geostatistical models, established that TB clusters in cattle herds and estimated the practical spatial ranges at which this occurs. Here this work is extended by taking into account possible anisotropy. Changes in spatial association over two time periods are also examined. The results have direct implications for establishing scale and direction in reactive culling. They are also of import regarding the evaluation of vaccines for badgers and cattle.
Epidemic modelling of bovine tuberculosis in cattle herds and badgers in Ireland
2020
Bovine tuberculosis, a disease that affects cattle and badgers in Ireland, was studied via stochastic epidemic modeling using incidence data from the Four Area Project (Griffin et al., 2005). The Four Area Project was a large scale field trial conducted in four diverse farming regions of Ireland over a five-year period (1997-2002) to evaluate the impact of badger culling on bovine tuberculosis incidence in cattle herds. Based on the comparison of several models, the model with no between-herd transmission and badger-to-herd transmission proportional to the total number of infected badgers culled was best supported by the data. Detailed model validation was conducted via model prediction, identifiability checks and sensitivity analysis. The results suggest that badger-to-cattle transmission is of more importance than between-herd transmission and that if there was no badger-to-herd transmission, levels of bovine tuberculosis in cattle herds in Ireland could decrease considerably.
Spatial modeling of clustering of TB-infection in badgers and cattle in Ireland
2010
Bovine tuberculosis (TB; caused by infection with Mycobacterium bovis) infects both cattle and badgers (Meles meles). Control of infection depends in part on our understanding of the spatial structure of the disease. Data from the Four Area Project, a large-scale intervention study aimed at assessing the effect of proactive badger culling on TB incidence in cattle herds, are analyzed for the first time using generalized linear geostatistical models [1]. We establish that infected herds are spatially correlated, but at a scale that varies with time and in different areas. Infected badgers are also shown to be spatially correlated and again the scale of spatial correlation is presented. Spatial correlation in herds is shown to persist following proactive badger removal. This is useful information for culling policy, suggesting that a single culling distance may not always be appropriate and that ongoing residual herd infection remains an issue unrelated to badgers.
Preventive Veterinary Medicine, 2016
The control of bovine tuberculosis (bTB) in cattle herds in the Republic of Ireland (ROI) is partially hindered by spill-back infection from wild badgers (Meles meles). The aim of this study was to determine the relative effects of interventions (combinations of culling and/or vaccination) on bTB dynamics in an Irish badger population. A spatial agent-based stochastic simulation model was developed to evaluate the effect of various control strategies for bovine tuberculosis in badgers: single control strategies (culling, selective culling, vaccination, and vaccine baits), and combined strategies (Test vaccinate/cull (TVC)), split area approaches using culling and vaccination, or selective culling and vaccination, and mixed scenarios where culling was conducted for five years and followed by vaccination or by a TVC strategy. The effect of each control strategy was evaluated over a 20-year period. Badger control was simulated in 25%, 50%, and 75% area (limited area strategy) or in the entire area (100%, wide area strategy). For endemic bTB, a culling strategy was successful in eradicating bTB from the population only if applied as an area-wide strategy. However, this was achieved only by risking the extinction of the badger population. Selective culling strategies (selective culling or TVC) mitigated this negative impact on the badger population's viability. Furthermore, both strategies (selective culling and TVC) allowed the badger population to recover gradually, in compensation for the population reduction following the initial use of removal strategies. The model predicted that vaccination can be effective in reducing bTB prevalence in badgers, when used in combination with culling strategies (i.e. TVC or other strategies). If fecundity was reduced below its natural levels (e.g. by using wildlife contraceptives), the effectiveness of vaccination strategies improved. Split-area simulations highlighted that interventions can have indirect effects (e.g. on population size) in non-treatment areas. Our model suggests that mixed control strategies could maintain infection prevalence to a low level for a considerable period even with a growing population. The model supported the hypothesis that culling strategies appeared to be the most effective method for the control of bTB in badgers using parameters, where available, from ROI, either singly or in combination with other strategies. In this model, the success of a vaccination strategy depended partially upon population density and the proportion of the population infected, therefore an initial culling program (to reduce density and/or remove infected badgers) followed by long-term vaccination may be effective in controlling bTB in badgers.
Modeling as a Decision Support Tool for Bovine TB Control Programs in Wildlife
Frontiers in Veterinary Science
Computer modeling has a long history of association with epidemiology, and has improved our understanding of the theory of disease dynamics and provided insights into wildlife disease management. A summary of badger bovine TB models and their role in decision making is presented, from a simple initial SEI model, to SEIR (inclusion of a recovered category) and SEI 1 I 2 (inclusion of two stages of disease progression) variants, and subsequent spatially-explicit individual-based models used to assess historical badger management strategies. The integration of cattle into TB models allowed comparison of the predicted impacts of different badger management strategies on cattle herd breakdown rates, and provided an economic dimension to the outputs. Estimates of R 0 for bovine TB in cattle and badgers are little higher than unity implying that the disease should be relatively easy to control, which is at odds with practical experience. A cohort of recent models have suggested that combined strategies, involving management of both host species and including vaccination may be most effective. Future models of badger vaccination will need to accommodate the partial protection from infection and likely duration of immunity conferred by the currently available vaccine (BCG). Descriptions of how models could better represent the ecological and epidemiological complexities of the badger-cattle TB system are presented, along with a wider discussion of the utility of modeling for bovine TB management interventions. This includes consideration of the information required to maximize the utility of the next generation of models.
Simulating the next steps in badger control for bovine tuberculosis in England
PLOS ONE, 2021
Industry-led culling of badgers has occurred in England to reduce the incidence of bovine tuberculosis in cattle for a number of years. Badger vaccination is also possible, and a move away from culling was “highly desirable” in a recent report to the UK government. Here we used an established simulation model to examine badger control option in a post-cull environment in England. These options included no control, various intermittent culling, badger vaccination and use of a vaccine combined with fertility control. The initial simulated cull led to a dramatic reduction in the number of infected badgers present, which increased slowly if there was no further badger management. All three approaches led to a further reduction in the number of infected badgers, with little to choose between the strategies. We do note that of the management strategies only vaccination on its own leads to a recovery of the badger population, but also an increase in the number of badgers that need to be va...
Simple model for tuberculosis in cattle and badgers
Proceedings of the National Academy of Sciences, 2005
As an aid to the study of bovine tuberculosis (TB), a simple model has been developed of an epidemic involving two species, cattle and badgers. Each species may infect the other. The proportion of animals affected is assumed relatively small so that the usual nonlinear aspects of epidemic theory are avoided. The model is used to study the long-run and transient effect on cattle of culling badgers and the effect of a period without routine testing for TB, such as occurred during the 2001 epidemic of foot-and-mouth disease in Great Britain. Finally, by examining the changes in cattle TB over the last 15 years, and with some other working assumptions, it is estimated that the net reproduction number of the epidemic is Ϸ1.1. The implications for controlling the disease are discussed.
Statistical Communications in Infectious Diseases, 2013
In Ireland and in the UK, bovine tuberculosis (bTB) infects cattle and wildlife badgers (Meles meles linnaeus) and badgers contribute to the spread of the disease in cattle. Isotropic and anisotropic spatio-temporal models are fitted to cattle herd and badger sett bTB incidence data from the Four Area Project using sequences of linear geostatistical models. An association was found between the spatial distribution of the disease in cattle and badgers in two of three areas. The limited association may be due to irregularity of sett territories, fragmentation of farms, TB-test insensitivity, temporal lags associated with transmission or non-spatial transmission. A statistical methodology is outlined whereby hypotheses related to spatial correlation structure may be tested.