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Defra urged to embrace PCR test to refine badger cull policy

Despite spending £360,000 on a trial, Defra appears to be unwilling to embrace a TB test its developers believe could be deployed to detect TB infection in badger setts to underpin a targeted culling policy.
The people behind the PCR test believe it could be deployed to help target badger culling
The people behind the PCR test believe it could be deployed to help target badger culling

Scientists and farmers behind a potentially ground-breaking TB testing technology are urging the Government to give it a chance, claiming it could help refine the badger cull policy.


They have spoken out in response to concerns there is little appetite to develop it further, despite the test showing potential in a Defra-funded study.


Researchers at Warwick University have been working on a qPCR (polymerase chain reaction) test for a number of years to establish whether, and how, it could be used to pick up TB infection in badger setts.


The PCR test has been championed by former Defra Secretary Owen Paterson, who hoped it could ultimately be deployed around farms to underpin a more ‘targeted’ badger culling policy.


A £360,000 Defra-funded study, commissioned by Mr Paterson in 2014, compared Warwick’s qPCR test with five others to establish which performed the best against certain criteria in detecting M.bovis from badger faeces.


The qPCR test, Test B in the chart below, came out top and was described as ’the best overall test’.

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The qPCR test met three out of the five criteria laid out, performing well on sensitivity, the ability to pick up infection. The paper concluded it showed ’good ability to detect low concentrations of M Bovis’.


It was considered ‘borderline’ on two criteria or although on one of these, sensitivity at sett level, this was resolved ’when spiked samples were analysed’.


It was also borderline on the requirement of 80 per cent specificity, suggesting it came up with too many ’false positives’ in what were actually clear samples.


The report concluded: "Only one test (qPCR) appears to be potentially suitable for taking forward to routine use.


"However, its borderline performance against some criteria highlight areas which may need further assessment and validation to fully understand the performance characteristics and utility of the test and hence determine if, and how, it could be best used practically.


"The potential practical use of a badger faecal test will also depend on future Defra policy and how the use of this test would fit alongside other interventions and control policies."


Based on these findings Defra and its TB Eradication Advisory Group appear to have rejected it, for now at least, according to Cornwall farmer Pat Bird, who has followed Warwick University's work on the trial.


Mrs Bird said she understood there had been no further contact with the Warwick team to tweak the qPCR test for ’wider use in the field’ as was intended by the trial.


Defra is not commenting on the study but is understood to be still considering its implications.


The big concern, however, even before cost and wider policy considerations, is that if it was used widely in the field, it would produce too many false positives, a problem that could also have political implications given the sensitivity surrounding badger culling.


The scientists, farmers and vets who have worked on the test insist, however, there is plenty of scope for further tweaking and more effort should be made to get it right.


They point to previous studies on the qPCR test by Professor Liz Wellington at Warwick, where using spring/summer samples, qPCR can achieved 100 per cent sensitivity in detecting disease in badger latrines.


It also achieved over 95 per cent specificity, meaning it produced very few ‘false positives’ when the test is used at the group level.

Key differences

This performance was achieved when the test was used at the 'optimum levels' developed by Warwick University. It would be unrealistic to expect these sort of results in the field, given the many variables involved, but those with an interest in the technology believe these figures highlight its potential.


According to Mrs Bird, key differences in the comparative study compared with the criteria developed by Warwick - for example, in the number of samples used, the background prevalence of infection and the volume of M. Bovis - reduced its benefits.


"This trial could be compared to using a recipe to make a loaf of bread, and adding half the amount of yeast the recipe demands: then being surprised when your loaf doesn’t rise to the occasion," she said.


She added: "We believe this test can make a major contribution to detecting infection in badger setts and forming the basis of a more targeted cull policy culling only where disease is present."


"But Defra needs to give it a chance to be tweaked and refined to shows it true potential, especially having invested so much getting this far and given the ill-fated vaccination programme has hit the buffers."


Gloucestershire dairy farmer, Nigel Finch, who took part in Warwick University’s qPCR sett screen test, said it could benefit farmers.


"We have used it, and had we been able to destroy the one sett which tested positive, out of 15 on this farm, we would probably not have lost 38 cattle on a recent test," he said.

PCR and TB

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