Badger social networks correlate with tuberculosis infection

Abstract

Although disease hosts are classically assumed to interact randomly [1], infection is likely to spread across structured and dynamic contact networks [2]. We used social network analyses to investigate contact patterns of group-living European badgers, Meles meles, which are an important wildlife reservoir of bovine tuberculosis (TB). We found that TB test-positive badgers were socially isolated from their own groups but were more important for flow, potentially of infection, between social groups. The distinctive social position of infected badgers may help explain how social stability mitigates, and social perturbation increases, the spread of infection in badgers.

Quantifying direct and indirect contacts for the potential transmission of infection between species using a multilayer contact network

“…It might be possible that these results are driven by the selection of latrine sites at which base stations were deployed, which tended to be towards the centre of the study site. This could potentially enhance any edge effects that result in badgers in social groups closer to the centre of the study site having higher centrality in the network We know from previous work that badgers that are test positive to M. bovis are more likely to occupy more connected roles within the badger social network (Weber et al, 2013b), and to use outlier setts away from the main communal burrow system more frequently at certain times of year (Weber et al, 2013a). These individuals could therefore act as "spread capacitors" that regulate the spread of infection in the badger population (Weber et al, 2013b;Silk et al, 2017a).…”

“…This could potentially enhance any edge effects that result in badgers in social groups closer to the centre of the study site having higher centrality in the network We know from previous work that badgers that are test positive to M. bovis are more likely to occupy more connected roles within the badger social network (Weber et al, 2013b), and to use outlier setts away from the main communal burrow system more frequently at certain times of year (Weber et al, 2013a). These individuals could therefore act as "spread capacitors" that regulate the spread of infection in the badger population (Weber et al, 2013b;Silk et al, 2017a). Given that network position within the badger social network is broadly reflective of the position of individuals in the full multilayer network, it seems likely that these individuals may also be integral in regulating transmission between hosts via the environment.…”

“…The end of a contact event is determined when two loggers have stopped detecting one another for a pre-set time period (30 seconds in this study). At this point the date/time and duration of the contact is logged, together with the identity of the encountered logger (Drewe et al, 2012(Drewe et al, , 2013Weber et al, 2013b). During the wider study (from September, 2009until September, 2010, proximity loggers were deployed on a total of 33 Welsh Black cattle, 61 badgers, and for some of the time at 19 base stations located at active badger latrines (Drewe et al, 2013).…”

“…Data were temporarily unavailable for some individuals if collar memory banks were full, collars were lost or for the calves in the herd prior to collaring. Contact data was available from approximately 70% of the adult badgers in the focal social groups in the study area (Drewe et al, 2013;Weber et al, 2013b). Data on latrine use were available from 13 latrines in total (Figure 1).…”

“…In badgers, direct transmission via inhalation of aerosolised bacteria (Cheeseman et al, 1989) and, to a lesser extent, biting (Jenkins et al, 2012) are suspected to be key routes for acquiring infection. Hence the distribution of infection in badgers is correlated with social network structure (Weber et al, 2013b). Direct cattle-cattle transmission is also well documented, and thought to occur predominantly via a respiratory route (Goodchild & CliftonHadley, 2001).…”