The first study to test for bovine TB in badgers on the edge of the cattle TB epidemic in England has shown that one in five badgers tested positive for the disease.
The pilot survey was carried out on road-killed badgers collected in Cheshire in 2014 through a local TB group that included farmers.
Scientists from the Universities of Nottingham, Liverpool and Lancaster tested the carcasses for the bacteria that cause bovine TB, Mycobacterium bovis (M.bovis), and found that around 20% were infected.
Furthermore, the strain of M.bovis found in Cheshire badgers was the same as that found in cattle in the same area.
The results of the study have been published in Scientific Reports.
Although there have been several published studies of bovine TB in badgers in the South West of England, where the infection is endemic in both cattle and badgers, this is the first study of infection in badgers on the expanding edge of the cattle epidemic.
Previous studies in Cheshire, from between 10 and 30 years ago when bovine infection was rare in the area, found only a few infected badgers in the south-east of the county.
However, while these findings strongly suggest that both badgers and cattle were part of the same geographically expanding epidemic in Cheshire, the direction of any cross-species transmission and the drivers of this expansion cannot be determined from this study.
Professor Malcolm Bennett from Nottingham University said: “The role of badgers in the geographic expansion of the bTB epidemic in England is not at all clear, and there is huge controversy surrounding the use of culling badgers to control the disease.
“While there is general agreement that in endemic areas the disease can be transmitted among and between cattle and badgers, the role of badgers in the expansion of the epidemic has not been studied.”
Prof Bennett added: “The epidemic could expand through cattle-to-cattle or badger-to-badger transmission, or a combination of the two with cross-species transmission.
“Determining whether or not badgers on the edge of the cattle epidemic have TB is the first step in unpicking this tangle of cause and effect, and examining badgers that had already been killed on the roads seemed the obvious way to collect the evidence for this pilot study,” he said.
At the time of planning the project, bovine TB in cattle in much of Cheshire was regarded as sporadic and it was intended that the study investigate the disease in badgers ahead of the epidemic front.
In the event, 2014 saw large increase in recorded bovine TB outbreaks in Cheshire herds, over a wider area than in previous years, and data from TB surveillance in cattle in Cheshire in 2014 were therefore included in this study for comparison with the findings in badgers through a collaboration with APHA both regionally and at Weybridge.
A more recent and larger study of infection rates in roadkill badgers in six counties on the edge of the cattle epidemic, core-funded by Defra and using much the same approach, is expected to publish its results early next year.
Bovine TB in cattle in Britain is concentrated in South West England and South Wales, but has been gradually spreading northwards in England.