December 17, 2019

expert reaction to a study looking at the transmission of TB between cattle and badgers

Research, published in the journal eLife, reports on the transmission of Tuberculosis (TB)  between cattle and badgers in Gloucestershire using genetic sequencing techniques. 

This roundup accompanied an SMC Briefing.

Prof Rosie Woodroffe, Senior Research Fellow, Zoological Society of London (ZSL), said:

“This is a very interesting study which shows how much information can be gleaned from modern genomics. The analyses suggest that the bacteria which cause bovine TB are transmitted from cattle to badgers as well as from badgers to cattle, although most transmission occurred within species. The authors are right to conclude that TB cannot, therefore, be eradicated just by managing badgers, or just by managing cattle. 

“The study was based on archived samples from a long-term study of badgers living at very high density in a well-wooded area of Gloucestershire. To get enough samples, the authors had to source cattle samples from a wider area (because cattle tend not to live in woodland) and over a longer time period. It would be very interesting to replicate this study in other areas, where more of the cattle and badgers occupy the same areas at the same time, and have greater opportunities to interact. 

“The really exciting element of the study is the possibility of using its methods to explore whether transmission probabilities vary between areas subjected to vaccination or culling.”

Prof Christl Donnelly, Professor of Statistical Epidemiology, University of Oxford and Imperial College London, said:

“This paper provides an interesting and important new perspective on the challenging problem of bovine TB in British cattle and badgers.  By using machine learning and analysing genetic data from the bovine TB pathogen (Mycobacterium bovis) in cattle and badgers in Woodchester Park (southwest England), the authors have shown that infected badgers are more likely to transmit to other badgers than to cattle.  Similarly, infected cattle are more likely to transmit to other cattle than to badgers.  Furthermore, badger-to-cattle transmission happens roughly 10 times as often as cattle-to-badger transmission. It will be interesting to see if similar results are obtained from other areas.”

Prof James Wood, Head of Department of Veterinary Medicine, University of Cambridge, said:

“This is an important and elegant piece of science, and the results are interesting in their quantification, albeit with some uncertainty, of what has been generally accepted to be the case scientifically for some time (although not by everyone around the polarised policy space). Bovine TB is an infectious disease of cattle, that transmits between cattle – and also from badger to badger. It also transmits from badgers to cattle and from cattle to badgers, but at slower rates than within species associated with close contact. The paper does not in itself target or inform specific controls in any obvious way.”

Prof Lord John Krebs, Emeritus Professor of Zoology, University of Oxford, said:

“This valuable study uses genomic information to work out the pathways of transmission of TB in Woodchester Park in Gloucestershire.  The genetic data demonstrate conclusively that TB is transmitted both from badgers to cattle and from cattle to badgers.  Although nearly ten times as much infection goes from badgers to cattle than from cattle to badgers, there is even more transmission of infection within each of the species.  In terms of policy, the results do not tell us whether killing badgers is more effective than controlling cattle to cattle transmission, but the fact that more infections are transmitted within species than between species suggests that controlling transmission among cattle is a priority in the strategy for eliminating TB.  One caveat is that Woodchester Park has a very high density of badgers, so the results may not be generalisable to all areas.”

‘Combining genomics and epidemiology to analyse bi-directional transmission of Mycobacterium bovis in a multi-host System’ by Kao et al. was published in eLife at 08:00 UK time on Tuesday 17th December. 

DOI: https://doi.org/10.7554/eLife.45833

Declared interests

Prof Woodroffe: “I was a member of the Independent Scientific Group on Cattle TB from 1998-2007, and have received research funding from Defra”

Prof Donnelly: “Prof Donnelly was deputy chair of the Independent Scientific Group on Cattle TB which designed, oversaw and analysed the Randomised Badger Culling Trial.  She contributed to the Bovine TB Strategy Review (chaired by Sir Charles Godfray) in 2018 and is a consultant on a Defra-funded project to compare bovine TB incidence in cattle herds in areas subjected to industry-led badger culling to those in unculled comparison areas.”

Prof Wood: “Funding in bTB research from BSBRC, DfID, ESRC, MRC, Defra, Gates. Sit on Defra’s TBEAG and Science Advisory Council. Head of Cambridge University Veterinary School”

None others received.