Badger sett TB test carries risks – Badger Trust
The Badger Trust has cautioned against government plans to develop a test that could identify badger setts infected with bovine tuberculosis.
DEFRA secretary Owen Paterson told a Commons committee last week that he was exploring the possibility of using PCR (polymerase chain reaction) tests to identify infected badger setts as part of a future badger culling strategy.
However, the Badger Trust has warned that the use of such a test to detect the presence of bovine TB cannot tell whether the infection came from cattle, badgers or any other wildlife.
In addition, the trust claims use of this test on its own carries “huge, counter-productive risks”.
Finding the bTB bacillus close to a sett would not in itself prove the origin of a sample and localised culling also raised the risk of perturbation, the trust warned.
David Williams, chairman of the Badger Trust, said: “PCR is a relatively crude tool at present. Further investigation must address many issues of concern before expectations about PCR are raised any more.
“Mr Paterson’s interest in PCR is just another extension of the coalition government’s unreasonable and blinkered preoccupation with badgers at a time when the urgent need is for progress with an effective cattle vaccine and an acceptable DIVA test to distinguish between vaccinated and infected cattle.”
Mr Paterson told the Environment, Food and Rural Affairs Committee that it would make an enormous difference if only diseased animals could be traced.
He said he had met “one of the world’s experts” and concluded there was “potential” for PCR to confirm disease in badger setts, and so target only infected badgers.
However, the Badger Trust said there was no guarantee that traces of bovine TB in or near a sett would mean all or even any of the animals in it would be infected. Furthermore, killing them all would run the risk of spreading the disease by stirring up the badger population.
Researchers at Warwick University have been working with the PCR test for several years. A recent paper described its use, but concluded that field studies were “now required to determine how best to apply the assay for population-level bTB surveillance in wildlife”.
But Mr Williams summarised difficulties for a practical field test:
- Did the sample come from cattle, badgers, foxes or other wildlife that could have walked through a farmyard, field or cow pat, any of them carrying infection?
- Did the sample come from a live badger or a long-dead one?
- If taken from soil, did it come from a badger?
If a positive sample was found in a sett:
- Would you catch and kill all the badgers in that sett?
- Would you catch and then test beside setts where an infected sample was found?
- A positive sample from inside a sett could be from a badger not normally living in that sett or a fox using it temporarily
- If you don’t identify and test all of the social group – a massive task – selective removal becomes impossible
- Infected badgers do not necessarily excrete the TB bacillus
- For a selective cull, expensive trapping will be required, unless you gas or poison the sett indiscriminately.