Genetic Distances between badgers (based on microsatellite-derived estimates of relatedness) and M. bovis isolates (based on pairwise SNP distances) alongside categories describing social group membership, age and sex categories

Pathogens rarely mix freely throughout host populations, and the presence
of barriers to transmission can be detected as patterns of increased
genetic isolation among pathogen isolates. Despite the importance of
transmission patterns in host societies and the risk of epizootics from
wildlife disease systems, barriers to open pathogen transmission are
poorly understood in wild hosts. We tested the influence of host kinship
and social structure on genetic divergence among strains of Mycobacterium
bovis, the causative agent of bovine tuberculosis, in a wild badger
population. We measured genetic distances between M. bovis isolates from
badger hosts that varied in their own genetic similarity (a proxy for
kinship) and in their social group affiliations. Using jack-knifing
analyses to control for pseudoreplication, we found that genetic distances
between pathogen isolates decreased with increasing kinship of host dyads,
but only when hosts shared the same social group.  Our findings
suggest that the open transmission of bTB in wild hosts is constrained by
a combination of social and kin structure, in particular the sharing of
similar pathogen strains among kin within social groups. We discuss the
implications of these transmission structures for the understanding and
management of wildlife disease.