Bovine tuberculosis in badgers in four areas in Ireland: Does tuberculosis cluster?
Department of Population Medicine, Ontario Veterinary College, University of Guelph, Clinical Research Building, Ont., N1G 2W1, Guelph, Canada. Preventive Veterinary Medicine
(Impact Factor: 2.17).
06/2003; 59(1-2):103-11. DOI: 10.1016/S0167-5877(03)00055-2
We described the distribution of badger populations in four different areas in the Republic of Ireland. The data came from periodic targeted badger-removal and subsequent post-mortem examinations conducted between 1989 and September 1997, and from a formal badger-removal project in the same areas from 1997 through 1999. Records were complete for 2292 badgers regarding the date of capture, tuberculosis status, geographical area and specific sett from where the badgers were snared. Of 3187 setts, 2290 had no badgers recorded against them (i.e. were inactive). The badger-level prevalence of tuberculosis differed among areas (range 13-29%). Badger populations were highly clustered by sett, and this result was similar over the four study areas. The median number of badgers per active sett was 2. Tuberculous badgers also clustered within a sett. The third quartile of tuberculous badgers was 1 per active sett. The prevalence of tuberculous badgers within a sett was not related to the total number of badgers. There was little evidence of spatial clustering with only one local cluster of tuberculous setts in each of three areas, and none in the fourth area. After adjusting for the number of badgers per sett, only one area had spatial clusters identified.
Available from: Graham C Smith
- "Bovine tuberculosis (TB), caused by Mycobacterium bovis, is a zoonotic disease and a serious economic burden on the cattle industry in parts of the world (Grange 2001; Smith 2004; Smith et al. 2004). European badgers (Meles meles) represent an important reservoir of M. bovis infection in Britain (Delahay et al. 1998) and Ireland (Olea-Popelka et al. 2003), and there is now conclusive evidence of their involvement in transmission to cattle (Donnelly et al. 2006; Independent Scientific Group 2007). Various badger-culling strategies have not prevented the rise in TB incidence in cattle in England and Wales, and cullinginduced social perturbation of badger populations is widely considered to have reduced the effectiveness of such approaches (Carter et al. 2007). "
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ABSTRACT: 1. We examine the effects of a combined badger test and vaccinate or remove
(TVR) strategy, on bovine TB in badgers and cattle herd TB breakdowns
(CHBs). We compare the results for a generic Northern Ireland situation with
a high prevalence area (County Down).
2. We use an existing simulation model previously used for Defra and the Welsh
Government, with some parameters updated as a result of recent scientific
publications, and use badger and cattle data derived from Northern Ireland
wherever possible. These include the best current estimate of the effect of
badger BCG vaccination in individual badgers.
3. Simulations of the TVR strategy (removing badgers that test positive and
vaccinating and releasing the others) resulted in relatively few badgers being
removed. Less than half the social groups had badgers removed in any one
year, and very few groups had more than one badger removed in any one
4. When the above level of removal was assumed to produce no social
perturbation then simulations predicted a reduction in the number of infected
badgers and CHBs.
5. When removal was assumed to result in social perturbation, simulations
predicted an increase in the number of infected badgers and CHBs in both the
area treated and around the edge. This arose because of the increased
transmission and the relatively high number of badgers left behind following
the intervention. It should be noted that there is no data yet available to
suggest what level of perturbation might be expected from a low level of
6. Initial recommendations for field deployment of a TVR study are provided.
These include starting the study with two trapping campaigns in the first year
and locating it in a high incidence area. Additionally it is important to monitor
the behaviour of badgers inside and outside the study area to look for
evidence of social perturbation, as this will help interpret the long term results
of the project.
Available from: Glenn Marion
- "However, bTB can persist where badger group sizes are below such levels, as is the case in Ireland where the mean badger group size has been estimated to be 3.9 (3.41-4.45) badgers per sett  with a different study observing a range of 1–14 badgers per sett . The persistence of disease at lower population levels may be enabled by variations in the social structure of the badger host population in different situations . "
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The persistence of bovine TB (bTB) in various countries throughout the world is enhanced by the existence of wildlife hosts for the infection. In Britain and Ireland, the principal wildlife host for bTB is the badger (Meles meles). The objective of our study was to examine the dynamics of bTB in badgers in relation to both badger-derived infection from within the population and externally-derived, trickle-type, infection, such as could occur from other species or environmental sources, using a spatial stochastic simulation model.
The presence of external sources of infection can increase mean prevalence and reduce the threshold group size for disease persistence. Above the threshold equilibrium group size of 6–8 individuals predicted by the model for bTB persistence in badgers based on internal infection alone, external sources of infection have relatively little impact on the persistence or level of disease. However, within a critical range of group sizes just below this threshold level, external infection becomes much more important in determining disease dynamics. Within this critical range, external infection increases the ratio of intra- to inter-group infections due to the greater probability of external infections entering fully-susceptible groups. The effect is to enable bTB persistence and increase bTB prevalence in badger populations which would not be able to maintain bTB based on internal infection alone.
External sources of bTB infection can contribute to the persistence of bTB in badger populations. In high-density badger populations, internal badger-derived infections occur at a sufficient rate that the additional effect of external sources in exacerbating disease is minimal. However, in lower-density populations, external sources of infection are much more important in enhancing bTB prevalence and persistence. In such circumstances, it is particularly important that control strategies to reduce bTB in badgers include efforts to minimise such external sources of infection.
Available from: Christian Gortázar
- "The M. bovis infection prevalence recorded in this study, especially in wild boar, is among the highest of the literature in wildlife populations. As a comparison, prevalences higher than 30% are rarely found in the badger ,  and in New Zealand possums . In deer species, the highest prevalence ever recorded was described in New Zealand, where an acute outbreak at prevalence higher than 90% in young fawns occurred in a farm . "
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ABSTRACT: Doñana National Park (DNP) in southern Spain is a UNESCO Biosphere Reserve where commercial hunting and wildlife artificial feeding do not take place and traditional cattle husbandry still exists. Herein, we hypothesized that Mycobacterium bovis infection prevalence in wild ungulates will depend on host ecology and that variation in prevalence will reflect variation in the interaction between hosts and environmental risk factors. Cattle bTB reactor rates increased in DNP despite compulsory testing and culling of infected animals. In this study, 124 European wild boar, 95 red deer, and 97 fallow deer were sampled from April 2006 to April 2007 and analyzed for M. bovis infection. Modelling and GIS were used to identify risk factors and intra and inter-species relationships. Infection with M. bovis was confirmed in 65 (52.4%) wild boar, 26 (27.4%) red deer and 18 (18.5%) fallow deer. In the absence of cattle, wild boar M. bovis prevalence reached 92.3% in the northern third of DNP. Wild boar showed more than twice prevalence than that in deer (p<0.001). Modelling revealed that M. bovis prevalence decreased from North to South in wild boar (p<0.001) and red deer (p<0.01), whereas no spatial pattern was evidenced for fallow deer. Infection risk in wild boar was dependent on wild boar M. bovis prevalence in the buffer area containing interacting individuals (p<0.01). The prevalence recorded in this study is among the highest reported in wildlife. Remarkably, this high prevalence occurs in the absence of wildlife artificial feeding, suggesting that a feeding ban alone would have a limited effect on wildlife M. bovis prevalence. In DNP, M. bovis transmission may occur predominantly at the intra-species level due to ecological, behavioural and epidemiological factors. The results of this study allow inferring conclusions on epidemiological bTB risk factors in Mediterranean habitats that are not managed for hunting purposes. Our results support the need to consider wildlife species for the control of bTB in cattle and strongly suggest that bTB may affect animal welfare and conservation.
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