A cattle herd in Great Britain can pass its statutory bovine TB tests and regain officially TB-free status while still carrying infection that causes a new breakdown later, and this "residual infection" is increasingly shaping how scientists and vets think about eradication, Farmers Weekly reports from the AberTB conference in Aberystwyth.
"It's been recognised that the standard skin test, in particular, even with severe interpretation, will not find every infected animal," said Professor James Wood of Cambridge University. The risk grows with herd size, since the chance of missing an infected animal is multiplied across more cattle; infected animals in a cleared herd may be the source of infection 12 months or so later, he said.
The disease is falling. In England, herd incidence fell by 1.4 to 6.4 in the year to June 2026, with herd prevalence at 3.4%; in Wales incidence fell 1.3 to 5.7 and prevalence 1.4 points to 4.3%, while Scotland keeps its officially TB-free status. TB-related slaughter fell 4% in England to 20,244 cattle and 23% in Wales to 10,090.
A more sensitive test is not a simple answer. Gamma interferon blood tests find more infected animals but can lead to many more cattle being removed, threatening herd viability and milk contracts. Sarah Tomlinson, technical director of the TB Advisory Service, said greater sensitivity means less specificity and more false positives: such animals are better treated as higher risk and managed, not necessarily culled at once.
Wood said research using whole-genome sequencing suggests about 15 times more cows are infected by other cows than by wildlife, which puts the focus on transmission within and between herds. Instead of a farm being simply free or not free, he said, existing test results and animal histories hold far more risk information. Projects in Pembrokeshire and North Wales are already using historic skin-test data to help farmers and vets identify and manage higher-risk cattle.
Wales' chief veterinary officer Richard Irvine said residual infection remains important even after a herd is declared free: "No test is perfect, so that's why we have a suite of approaches, a suite of controls."
Source: Farmers Weekly
Comments
(0)