This world-first application of bacterial whole-genome sequencing to investigate the spread of bovine TB provides the first direct evidence of ongoing transmission between cattle and between cattle and badgers at the individual farm level.

The new study was based on AFBI’s detailed historical analysis of the strains of TB bacteria associated with recurrent TB outbreaks in local cattle herds. The complete genetic sequence (4.3 million bits of genetic information) of each individual TB organism, isolated by AFBI from 26 cattle in 5 herds and 4 badgers found dead on roads in the vicinity of those herds, was analysed.

Genetic mutations which accumulate as the bacteria spread between animals were tracked and used to determine the relatedness of the isolates.

Dr Robin Skuce, who led the AFBI research team, said “This study shows that the genetic sequences of the TB bacteria isolated from cattle and badgers found in the vicinity of the herds were very highly related, and in some cases they were indistinguishable. There was also evidence of ongoing cattle-to-cattle transmission occurring in some of the herds studied.

"Bovine TB is notoriously difficult to control, not least because we don’t fully understand how it is transmitted between animals. Whilst badgers have been identified as a significant wildlife reservoir with the potential to infect cattle, direct evidence of ongoing transmission of TB between badgers and cattle at farm level has been lacking," said Dr Skuce.

"This relatively small study demonstrates the tremendous potential of this new genetic sequencing technology to allow the spread of disease to be better understood," added Mr Professor Rowland Kao of the University of Glasgow, who led the study, explained.

“This study provides new evidence of the close relationship between bovine TB infections in cattle and badgers at farm level. However, we can’t yet determine the direction or extent of transmission between cattle and badgers.

"Application of this technology to a larger number of cattle herds and badgers has the potential to provide valuable information on the significance of badger-to-cattle and cattle-to-cattle spread of infection and to help us to inform disease control policies reliably.”