Defra-funded) research (www.cam.ac.uk/research/news/scientists-build-a-clearer-picture-of-the-spread-of-bovine-tuberculosis/) has confirmed just how unreliable the skin test is. The RethinkbTB discussion paper (page 7, 'Why test and cull is not working') makes similar conclusions but the latest research makes it even more unreliable. It is this 'imperfect' test that is the backbone of the existing system. Clearly it is not good enough.
Scientists at Cambridge have used mathematical tools to develop models for estimating the efficiency of cattle-based controls for bovine tuberculosis (bTB).
The models built by the team represent an advance over previous models as they are informed directly by extensive data on reported incidence and spread of the disease, rather than expert opinion. Importantly, they provide a first estimate of the quantity of infection missed by cattle testing and the contribution of this hidden burden of infection to the persistence of bTB within herds.
Applied to recent data, the models suggest that around one in five of British herds that have been cleared of restrictions, following testing for bTB, may harbour the infection. It also points to a higher incidence, and faster spread, of the disease in large herds. The research focuses on the cattle-to-cattle transmission of bTB within herds.
“Many aspects of bTB, and its transmission, remain a mystery – and it’s long been known that the protocol and testing methods used to diagnose the disease are far from perfect. One of our models suggests that up to 21 per cent of herds may be harbouring infection after being cleared from movement restrictions,” said James Wood, Alborada Professor of Equine and Farm Animal Science at Cambridge University.
“However, our models also estimate a high rate of re-introduction of infection into herds, particularly in high incidence areas. This rate of re-infection is high enough that even if improvements in testing eliminated the hidden burden of infection, rates of recurrence would not be reduced.”