Culling and cattle controls influence tuberculosis risk for badgers

Abstract

Human and livestock diseases can be difficult to control where infection persists in wildlife populations. In Britain, European badgers (Meles meles) are implicated in transmitting Mycobacterium bovis, the causative agent of bovine tuberculosis (TB), to cattle. Badger culling has therefore been a component of British TB control policy for many years. However, large-scale field trials have recently shown that badger culling has the capacity to cause both increases and decreases in cattle TB incidence. Here, we show that repeated badger culling in the same area is associated with increasing prevalence of M. bovis infection in badgers, especially where landscape features allow badgers from neighboring land to recolonize culled areas. This impact on prevalence in badgers might reduce the beneficial effects of culling on cattle TB incidence, and could contribute to the detrimental effects that have been observed. Additionally, we show that suspension of cattle TB controls during a nationwide epidemic of foot and mouth disease, which substantially delayed removal of TB-affected cattle, was associated with a widespread increase in the prevalence of M. bovis infection in badgers. This pattern suggests that infection may be transmitted from cattle to badgers, as well as vice versa. Clearly, disease control measures aimed at either host species may have unintended consequences for transmission, both within and between species. Our findings highlight the need for policymakers to consider multiple transmission routes when managing multihost pathogens.behavior ͉ bovine tuberculosis ͉ epidemiology ͉ Meles meles ͉ perturbation

The prevalence, distribution and severity of detectable pathological lesions in badgers naturally infected withMycobacterium bovis

“…The selected nature of the samples of animals examined in these previous studies, and in some cases the small numbers of animals included, may account for differences in values obtained for the proportions of animals showing visible lesions or severe pathology. RBCT findings have shown that the prevalence of infection can differ spatially both at the level of badger social groups and region [19] suggesting that samples of animals drawn from a small number of groups may not be representative of the wider population. We acknowledge three potential sources of bias in the sampling method.…”

“…There is evidence that such storage may reduce the sensitivity of detecting M. bovis by culture [18]. Analyses conducted using data from proactive areas in the RBCT showed a borderline significant association between being culture negative for M. bovis and having been stored for more than 7 days [19]. As our main interest in these analyses is the pathology in tuberculous badgers and freezing is also likely to have influenced detection of lesions at necropsy, data for all carcases stored for more than 7 days were excluded from the analysis.…”

Assessing spatiotemporal associations in the occurrence of badger–human conflict in England

“…Rather, increases occurred at greater distances than we predicted and were sustained up to scales of 4,000 m. Thus, it is perhaps most likely that the few observed excesses of cases represented a statistical artefact, especially in light of the number of comparisons performed when assessing multiple scales. Alternatively, spatiotemporal analyses can be affected by the influence of confounding factors (for a discussion in an epidemiological context, see Wakefield et al 2000). An apparent excess of new problem cases following management action at badger setts could reflect spatial and temporal heterogeneity in phenomena related to badger or human populations.…”

Badger responses to small-scale culling may compromise targeted control of bovine tuberculosis

“…Selective culling of test-positive cattle has helped to eradicate TB across much of the developed world, but eradication from the United Kingdom is impeded by M. bovis infection in European badgers (Meles meles) (8), as well as by continued transmission among cattle (9)(10)(11). Transmission has also been documented among badgers (12), from cattle to badgers (13), and from badgers to cattle (14,15). Because badgers are clearly a contributing factor to the UK's TB problem, successive TB control policies have included culling of badgers (7,8).…”