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THERE are times when waiting for a government announcement on bovine tuberculosis (tb) seems like waiting for a bus: you hang around for what feels like ages and then three turn up at once. This was certainly the case last December, when defra announced that it would be introducing premovement testing of cattle, new compensation arrangements for farmers whose cattle had to be culled, and a consultation on whether badgers should be culled to help control the disease in cattle. There was then a gap of about six months before defra concluded, somewhat predictably, that it was still too soon to reach a decision on badger culling because, as the Secretary of State, Mr David Miliband, put it, there were ‘too many unknowns’. (For some, this was like the bus that finally arrives, only to depart empty for the depot.) Now, a few weeks later, there has been another group of three announcements from defra, concerning the gamma-interferon (γ-ifn) blood test, a report on intradermal tuberculin testing procedures, and the recently observed fall in the number of new incidents of bovine tb.
News that the γ-ifn test is finally to be included in Great Britain's testing programme is welcome, not least because it has been awaited for some time. The test is more sensitive, but less specific, than the intradermal tuberculin test; however, used in conjunction with the tuberculin test, it should help improve the sensitivity of the testing programme. Under the policy announced by defra, the γ-ifn test will be used more extensively in England and Wales from October 2006, with the result that the number of tests performed will almost triple, to about 50,000 per year. It will be used alongside the tuberculin test and should help speed up testing and improve detection rates in problem herds. It will mainly be used in an attempt to prevent infection becoming established in new areas, as well as being available for use as a disease control tool in existing tb ‘hotspots’. As the new testing regime is introduced and becomes established, it will be important to monitor the results carefully, both to determine its impact and assess the specificity of the γ-ifn test to a greater extent than has been possible from the trials that have been conducted so far.
News that the State Veterinary Service (svs) is to review procedures for carrying out the intradermal tuberculin test is also welcome, and provides an opportunity to bring them up to date with modern farming practice. The announcement follows a defra-commissioned review of procedures, undertaken by the risk management firm dnv Consulting. This did not identify any factors that would fundamentally undermine the validity of the tb testing process as a disease control measure. However, it did find evidence of variation in the way the test was conducted, and the report makes a number of recommendations for improvements. They include a thorough review of the current procedures manual; a review of svs procedures for the approval and monitoring of local veterinary inspectors (lvis); an assessment of how information technology could support the testing process; and possible improvements to equipment. There is no doubt that current standard operating procedures can cause difficulties in the field, and both the bva and the British Cattle Veterinary Association have said that they look forward to working with defra and the svs in implementing the report's recommendations and helping to revise the procedures.
The decline in the number of new tb incidents is discussed in a statement by the Chief Veterinary Officer (cvo), Dr Debby Reynolds. Based on an analysis of the most recent data, she concludes that there has been a real reduction in the number of new bovine tb incidents over the past six months compared with the previous 12 to 18 months, and that the number of new incidents is now similar to that in the same period in 2004. She notes, however, that levels remain high in comparison with other eu countries, and well above the levels previously experienced in the uk. She rightly points out that it is still too early to draw any firm conclusions as to whether this is a temporary change or the start of a sustained reduction, noting that ‘tb is a disease with a long incubation, and the incidence varies seasonally. We would need to consider whether this pattern of decline is maintained over a full year before reaching any firmer conclusions.’
The cvo and her team are unable to explain the decline, although they do rule out some of the factors that have been suggested as a possible cause, such as the change, since October 2005, in the source of tuberculin used in the skin test. The cvo remarks, ‘The reduction is likely to be caused by a complex combination of factors. Our analysis to date has enabled us to rule out some factors, and we may be able to improve our understanding further as the amount of data increases, but it is highly unlikely that it will be possible to explain the decline with any precision.’
While encouraging, the apparent decline in the number of new incidents cannot be explained and, at this stage, it cannot be interpreted as indicating the start of a downward trend. There are certainly no grounds for complacency; every effort must be made to contain the disease, and farmers, veterinarians and government must work together to strengthen and develop the control measures available.
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