Survey reveals bovine TB in a fifth of roadkill badgers in Cheshire


6 December 2018 14:53
badgers

The first study to test for bovine tuberculosis 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 stakeholder TB Group that included farmers, wildlife groups and vets. 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 per cent were infected.

Furthermore, the strain of M.bovis found in Cheshire badgers (SB0129 or genotype 25) was the same as that found in cattle in the same area. The results have been in Scientific Reports.

Although there have been several published studies of bovine TB (bTB) 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.

Dr Chris Jewell, from Lancaster’s Centre for Health Informatics, Computing and Statistics (CHICAS), said: “This study highlights the importance of modern spatial statistics and machine learning in addressing important questions in UK livestock farming and food safety.

“From data on bovine TB prevalence in badgers collected in Cheshire, on the edge of the expanding TB epidemic in cattle, we are able to show that infection in both species is associated in space. This work represents the first step towards identifying how infection may flow between the two species, and forms a firm basis for our ongoing work to provide rigorous, data-driven information for aid bovine TB control strategy in England.”

Professor Malcolm Bennett, from Nottingham University’s School of Veterinary Medicine and Science, added: “As emphasised by the recent independent review led by Professor Sir Charles Godfray, 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. 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.”

An important aspect of the study was that it arose from, and relied on, a variety stakeholders in Cheshire. It came about through the Cheshire TB Eradication Group, which brings together farmers, vets, wildlife groups and others to discuss bTB in the county and provide all those involved with the latest information and advice on how to stop the disease’s spread. The study was designed by the Group, and members collected the carcasses of road-killed badgers, which were then analysed through a collaboration between the Universities of Liverpool, Nottingham and Lancaster.

At the time of planning the project, bTB in cattle in much of Cheshire was regarded as sporadic and it was intended that the study investigate bTB in badgers ahead of the epidemic front. In the event, 2014 saw large increase in recorded bTB 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 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.

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