# Sociality and kinship constrain the free-mixing of pathogens in a wild mammal host population

## TL;DR

This study shows that social and family ties in wild badgers limit the spread of tuberculosis, with close relatives in the same group sharing similar strains.

## Contribution

The study reveals that both kinship and social group membership constrain pathogen transmission in wild hosts.

## Key findings

- Genetic distances between M. bovis isolates decreased with increasing host kinship.
- This effect was observed only when hosts belonged to the same social group.
- Transmission of bTB is constrained by social and kin structures in wild badger populations.

## Abstract

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 (bTB), 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 diseases.