Genetic clues of TB spread between cows and badgers revealed

TB in cattle can be spread by badgers, but cow-to-cow transfer more significant – research

The first direct evidence of how bovine tuberculosis (TB) transmits infection between badgers and cattle has been revealed.

The research by scientists at UCD and the University of Edinburgh shows TB in cattle can be spread by badgers, but cow-to-cow transmission is much more significant than badger-to-cow.

TB in cattle and badgers passes between members of the same species at least twice as often than between cow and badger, the study finds.

Bovine TB is a chronic, highly infectious disease causing huge losses in affected farms in Ireland and the United Kingdom. The Irish control programme for bovine TB cost farmers, the exchequer and European Union €84 million in 2017.


The researchers examined genetic data from the bacteria that causes the disease also found cattle are approximately 10 times more likely to catch TB from badgers than badgers are to catch it from cattle.

The breakthrough should enable more focused management of badger populations, according to Dr Joseph Crispell of UCD School of Veterinary Medicine, a lead researcher in a study published on Tuesday in the journal eLife.

Culling of badgers to curb bovine TB is a contentious issue among veterinary and wildlife experts – and animal welfare campaigners – though the scientific and farming consensus is a “wildlife reservoir” of infected badgers sustains the disease, which originally began in cattle.

The research, which was conducted in Gloucestershire over a 15-year period, “could improve control strategies, reduce disease transmission and cut associated costs”, said Dr Crispell – though further analysis needs to be conducted in different regions.

Their study was conducted in an area where there was known to be high badger populations while the same genetic and data collecting techniques were now being applied in Co Wicklow.

Bovine TB is an infectious respiratory disease of cattle mainly spread through inhaling infectious particles in the air. It is caused by the bacterium Mycobacterium bovis, which can also infect and cause disease in other mammals, including humans, deer, goats, pigs, cats and dogs.

"Using data from an undisturbed population of badgers in Woodchester Park in Gloucestershire and nearby cattle farms, this study provides the first direct evidence of transmission between badgers and cattle. It is an area where tuberculosis is known to occur frequently in both cattle and badgers," he explained.

The researchers analysed the entire genetic make-up of the bacteria from 230 badgers and 189 cattle, a process known as whole genome sequencing. They combined this with detailed information on where the cattle and badgers lived, when they were infected, and whether they could have had contact with one another.

‘Direct evidence’

Scientists were then able to estimate how often the two species spread TB. They confirmed badgers play an important role in the maintenance of the disease in this area.

Prof Rowland Kao of the University of Edinburgh said the study provided not mere observation and inference but "direct evidence" that "changes the nature of the game".

“Current approaches to controlling bovine TB only discriminate at a very coarse, regional level between areas where badgers are more likely to be involved in infecting cattle from areas where they are not. This work identifies genetic signatures that could guide the interpretation of similar data if collected in other, less-intensively studied areas,” he added.

“This would allow for a more targeted control of tuberculosis in cattle and badgers, aiding efforts to control the disease and reduce the impact on the badger population” Additional reporting – Guardian

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times