The ecology of pathogen transmission between wildlife and livestock
Creators: name: Ham, Cally
Publisher: name: Imperial College London
Year: 2019

description: Bovine tuberculosis (TB) is recognised as the most important endemic disease affecting the farming industry within the UK. Difficulties in eradicating the disease from the national cattle herd are thought to be in part due to transmission of Mycobacterium bovis (the causative agent of TB) between cattle and wildlife, especially badgers (Meles meles). Whilst it is known that badger-to-cattle and cattle-to-badger transmission of M. bovis is possible, it is less clear when and where these transmissions occur. In the first half of this thesis I investigate two potential locations of interspecific contact; badger activity within cattle grazed pasture fields (Chapter Two) and cattle activity at badger latrines (Chapter Three). I find that badgers preferentially forage in pasture fields that were occupied by cattle 8-14 days previously. Badgers preferred pasture fields occupied by cattle 8-14 days previously, and avoided fields occupied by cattle &gt;35 days previously. These results suggest that badgers preferred to forage on short swards rather than taking advantage of earthworm accumulations under cowpats. This information could be used to ensure cattle do not return to fields during the period when badgers are most likely to be present, and provides a practical way to reduce opportunities for badger-to-cattle transmission of M. bovis. Whilst badger activity in pasture fields gives a broadscale picture of where and when interspecific contact might occur, in Chapter Three I use camera traps to look at badger latrines as a small-scale landscape feature where badger-to-cattle contact might occur. I find that badgers continue to use latrines located in fields occupied by cattle and that cattle graze and sniff at badgers latrines within the environmental survival time of M. bovis. These results suggest that badger latrines are a potential location of cattle infection with M. bovis and that landowners should consider the location and management of badger latrines when cattle are at pasture. The badger population is managed throughout the UK with the aim of reducing badger-to-cattle transmission of M. bovis. Currently, both badger culling and vaccination are used in England, Wales and Northern Ireland. In the second half of this thesis I investigate how effective badger culling might be at a large-scale (Chapter Four) and at a smaller scale (Chapter Five). I find that, under the currently used badger culling protocol in England, culling is associated with an increase in individual badger ranging behaviour. The increased ranging among surviving badgers potentially increases the opportunities for both badger-to-cattle and badger-to-badger contact and therefore increases the potential for the transmission of infection from surviving badgers. Additionally, I find that within a culled area individual badgers are active for less time each night, potentially reducing their accessibility to marksmen. Finally, I investigated the potential effectiveness of badger management programmes (culling or vaccination) conducted at a single-farm level. The results suggest that disease management programmes should target multiple farms in order to be most effective for the target farm. However, the area around the target farm that needs to be included in a management programme is smaller for vaccination than for culling due to the increase in badger ranging behaviour associated with badger culling. Within this thesis I provide new information useful in understanding when and where badger-to-cattle transmission of M. bovis might occur and in designing effective management programmes. The results presented, whilst specific to this system, might also inform management protocols for other diseases transmitted between wildlife and livestock.