To ask Her Majesty's Government how many cattle have been tested positive for bovine tuberculosis and then following slaughter have been negative on post-mortem testing; and what progress has been made in producing an accurate test before cattle are slaughtered.
The early detection and removal of tuberculosis (TB)-infected cattle before they develop advanced pathology and/or clinical signs of the disease (and thus become highly infectious) is a key element of bovine TB eradication programmes, including England’s 25 Year Bovine TB Strategy. To that effect, we use ante-mortem tests that measure the animals’ immune response to infection with the bovine TB bacterium (Mycobacterium bovis – M. bovis), rather than rely on direct detection methods.
The single intradermal comparative cervical tuberculin (SICCT) test, commonly known as the ‘skin test’, together with the interferon-gamma release assay (IGRA), is the legal standard approved in the EU legislation for the diagnosis of TB in live cattle in the UK. As with cases of TB in humans, only a proportion of those animals infected with M. bovis and reacting to a tuberculin skin test or IGRA display gross lesions of TB when subjected to post-mortem meat inspection in the slaughterhouse.
In 2017 (the last year for which an analysis of post-mortem findings is available), approximately 60% of the 32,000 cattle compulsorily removed for bovine TB control reasons in England as skin test reactors or IGRA positives did not have visible lesions of TB on post-mortem and were also negative for M. bovis on bacteriological culture (where performed).
Defra and the Animal and Plant Health Agency (APHA) are constantly striving for new ways to maximise the effectiveness of TB testing of cattle to achieve the objectives of the Strategy. APHA may exceptionally authorise the private use of non-validated diagnostic tests for bovine TB in herds where the disease is persistent, in order to help detect additional infected animals that may have been missed by the approved official tests (rather than to negate a positive result to such tests). A policy position paper on non-validated diagnostics for TB in cattle is now available on the APHA Vet Gateway (http://apha.defra.gov.uk/vet-gateway/index.htm).
Over £4 million was allocated to TB research and development in 2018/19, with the anticipation of a similar spend this financial year. The majority of these finds are being invested in improving diagnostic tests alongside vaccine development. However, validation for a new test to World Organisation for Animal Health standards would only lead to official adoption if it demonstrated proven advantages in the detection of disease alongside the current test portfolio.