Inferring Mycobacterium bovis transmission between cattle and badgers using isolates from the Randomised Badger Culling Trial

Abstract

Mycobacterium bovis (M. bovis) is a causative agent of bovine tuberculosis, a significant source of morbidity and mortality in the global cattle industry. The Randomised Badger Culling Trial was a field experiment carried out between 1998 and 2005 in the South West of England. As part of this trial, M. bovis isolates were collected from contemporaneous and overlapping populations of badgers and cattle within ten defined trial areas. We combined whole genome sequences from 1,442 isolates with location and cattle movement data, identifying transmission clusters and inferred rates and routes of transmission of M. bovis. Most trial areas contained a single transmission cluster that had been established shortly before sampling, often contemporaneous with the expansion of bovine tuberculosis in the 1980s. The estimated rate of transmission from badger to cattle was approximately two times higher than from cattle to badger, and the rate of within-species transmission considerably exceeded these for both species. We identified long distance transmission events linked to cattle movement, recurrence of herd breakdown by infection within the same transmission clusters and superspreader events driven by cattle but not badgers. Overall, our data suggests that the transmission clusters in different parts of South West England that are still evident today were established by long-distance seeding events involving cattle movement, not by recrudescence from a long-established wildlife reservoir. Clusters are maintained primarily by within-species transmission, with less frequent spill-over both from badger to cattle and cattle to badger.

European badger (Meles meles) responses to low‐intensity, selective culling: Using mark–recapture and relatedness data to assess social perturbation

“…Between-host transmission has been difficult to demonstrate and quantify. Recent phylodynamic studies by Crispell et al (2019) and van Tonder et al (2021), using M. bovis genomes from Woodchester Park and the Randomized Badger Culling Trial (RBCT) in GB, respectively, demonstrated inter-species transmission events were rare compared to intra-species ones (i.e. cattle-to-cattle transmission).…”

Analysis of a multi-type resurgence of Mycobacterium bovis in cattle and badgers in Southwest France, 2007-2019

“…Although the epidemiological units are different, the CB/BC ratios we obtained can be qualitatively compared with those obtained in phylodynamic studies, which were > 1 in some studies [ 61 , 62 ], and < 1 in other [ 63 ]. In England, Tonder et al recently analyzed retrospectively 12 putative transmission clusters reported between 1999 and 2008, and found CB/BC ratios > 1 in four clusters, and < 1 in the eight other [ 64 ]. In our study area, Duault et al [ 65 ] found a CB/BC ratio < 1.…”

Disturbance Ecology Meets Bovine Tuberculosis (bTB) Epidemiology: A Before-and-After Study on the Association between Forest Clearfelling and bTB Herd Risk in Cattle Herds

“…The mechanism for these patterns cannot be inferred from these retrospective models, but we speculate that it may involve the disturbance of wildlife [ 48 ]. Badgers ( Meles meles ) and, to a lesser extent, deer species, are a known wildlife host of bTB and are involved in the epidemiology of infection in local cattle herds [ 26 , 32 , 36 , 49 ]. Disturbances, such as road building and badger culling, are known to affect the socio-spatial structure of badger populations and can lead to the increased movement of animals amongst social groups (e.g., [ 50 , 51 , 52 ]).…”