Badgers may not spread TB to cattle through direct contact
Badgers may not transmit TB to cattle by direct contact, according to new research.
A study suggests that cows contract the disease by coming into contact with infected faeces and urine in pasture.
The scientists involved suggest that advice given to farmers to control the spread of the disease may need to be reassessed.
The research has been published in Ecology Letters.
Scientists have known for 40 years that badgers transmit TB to cattle and, more recently, probably vice versa. But no one knows exactly how the disease is transmitted.
To find out whether it is by direct contact, researchers tracked the movement of hundreds of cattle and badgers using collars with GPS and proximity sensors across 20 farms in Cornwall.
Despite the fact that the collared cattle spent the equivalent of nearly 15 years in the home ranges of GPS collared badgers, the two species were never found in close proximity.
The researchers found there was not a single instance of direct contact and there was also some evidence that if anything badgers avoid the bigger animals, with the tracking data indicating that the creatures preferred to be at least 50 metres away from the cattle.
Current control measures recommended by the Department for the Environment, Food and Rural Affairs (Defra) assume that direct contact is an important method of transmission.
According to the lead author, Prof Rosie Woodroffe of the Zoological Society of London, advice to farmers will now need to be re-assessed.
"There are loads and loads of things that farmers are being advised to do and there is no certainty that any of them will actually work and because of this, hardly any farmers implement any of these sorts of measures," she told BBC News.
"If we can focus on the things most likely to work on that massive array of things farmers are being advised to do more people will do them."
Prof Woodroffe and her colleagues are now trying to identify how the disease is transmitted. The most likely possibility is that it is through badger faeces and urine which may leave the TB infection in grazing pasture for many months.
This would help to explain why it takes so long for culling badgers to have an effect - because the infection they have left in the environment can last for months.
If that is the case it raises the possibility that some cattle-to-cattle transmission is happening through the environment. That is important because TB in cattle is managed as a contagious disease and assumes that cows need to be in close contact with each other to get the disease.
If there is a possibility that some cattle-to-cattle transmission is happening through the environment, Defra will have to consider whether to modify its control measures further, according to Prof Woodroffe.
"We are now beginning to identify how the transmission happens and that ought to open up an array of finely tuned management approaches instead of the blunt instrument we have now," she says.
In response to the findings of the study a Defra spokesperson said:
"Our comprehensive strategy to beat bovine TB includes tighter cattle controls, good biosecurity and badger control in areas where the disease is widespread, and a number of measures are in place to prevent the spread of infection.
"These include frequent testing and rapid removal of infected cattle, pre- and post-movement testing and wildlife proofing of high risk units. To reduce the risk of cattle-to-cattle transmission from contaminated environment, farmers are required to carry out cleaning and disinfection and to keep cattle out of fields grazed by reactors for two months after their removal. There are also rules about the use of manure and slurry on infected farms to mitigate the risks associated with their spread."
Defra is expected to extend its badger cull to seven new parts of South West England to help control the spread of the disease at the end of this month.
The department is understood to have received 29 applications and expressions of interest for extensions of the cull in areas thought to include South Devon, North Gloucestershire, Herefordshire and North Cornwall.
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