Social group size affects Mycobacterium bovis infection in European badgers (Meles meles)

Abstract

Summary 1.In most social animals, the prevalence of directly transmitted pathogens increases in larger groups and at higher population densities. Such patterns are predicted by models of Mycobacterium bovis infection in European badgers ( Meles meles ). 2. We investigated the relationship between badger abundance and M. bovis prevalence, using data on 2696 adult badgers in 10 populations sampled at the start of the Randomized Badger Culling Trial. 3. M. bovis prevalence was consistently higher at low badger densities and in small social groups. M. bovis prevalence was also higher among badgers whose genetic profiles suggested that they had immigrated into their assigned social groups. 4. The association between high M. bovis prevalence and small badger group size appeared not to have been caused by previous small-scale culling in study areas, which had been suspended, on average, 5 years before the start of the current study. 5. The observed pattern of prevalence might occur through badgers in smaller groups interacting more frequently with members of neighbouring groups; detailed behavioural data are needed to test this hypothesis. Likewise, longitudinal data are needed to determine whether the size of infected groups might be suppressed by disease-related mortality. 6. Although M. bovis prevalence was lower at high population densities, the absolute number of infected badgers was higher. However, this does not necessarily mean that the risk of M. bovis transmission to cattle is highest at high badger densities, since transmission risk depends on badger behaviour as well as on badger density.

Modelled impacts of badger culling on cattle TB in a real area with geographic boundaries

“…However, it is notable that dataset 1 conforms to a pattern whereby, within culling areas, the benefits of badger culling increase with increasing distance from the culling area boundary, while adverse impacts predominate on the periphery of culling areas; effects which are consistent with a range of findings suggesting that changes to the ways in which badgers interact are more pronounced close to culling area boundaries (Donnelly and others 2003, Woodroffe and others 2006, 2009, Donnelly and others 2007, Jenkins and others 2010a). …”

“…Such increased transmission may be related to changes in bTB prevalence in badgers, which Woodroffe and others (2009) have shown can be consistently higher at low badger densities, within small social groups, and among badgers whose genetic profiles suggested that they have immigrated into social groups, although the absolute number of infected badgers has been found to be higher at higher population densities.…”

Mapping Brucellosis Increases Relative to Elk Density Using Hierarchical Bayesian Models

“…Few datasets exist for natural systems that address the relationship between host density and pathogen transmission [but for timeseries analyses see: 46], [47], [48]. We showed that the seroprevalence of brucellosis in Wyoming elk is increasing in some regions where elk are not artificially aggregated onto supplemental feeding grounds and these increases in seroprevalence are correlated with elk densities at the hunt area scale (Fig.…”

Density and abundance of badger social groups in England and Wales in 2011–2013

“…Evaluation of the ecological impact of badger culling during the Randomised Badger Culling Trial identified an increase in fox abundance associated with reductions in badger density26 while reciprocal relationships between hedgehog Erinaceus europaeus and badger distributions suggest that increasing badger numbers might have had a negative impact on hedgehogs27. In terms of tuberculosis epidemiology, at a local level, disease prevalence and incidence appears to vary with mobility among groups28 and prevalence has been shown to be higher in smaller social groups29. Consequently, despite a broad landscape scale correlation between the incidence of TB in cattle and the distribution of badgers30, badger social group density alone may not predict patterns of TB infection in badgers or cattle.…”