Bovine TB: Eleventh TB Advisory Group meeting - Friday 7th March 2008
Summary of discussion
1. The Group met with representatives from the Veterinary Laboratories Agency (VLA) and the Central Science Laboratory (CSL) to hear about their work and to have an overview of Defra’s bTB research programme.
2. The Chairman began by welcoming Professor Quintin McKellar, Chairman of the new bovine TB Science Advisory Body (bTB SAB) who joined part of the meeting. The Chairman invited Professor McKellar to briefly explain bTB SAB’s role. Professor McKellar stated that the bTB SAB was set up specifically to focus on science and they were tasked with looking at the research on bTB to consider whether it was right for policy development. Professor McKellar confirmed the two Groups had very different remits, his would focus on science informing policy and the TB Advisory Group focused on advising on policy development and implementation. However, he acknowledged that the two Groups could not work in isolation and bTB SAB would keep the TB Advisory Group updated on any relevant information and developments of interest to it.
3. Richard Clifton-Hadley from the Veterinary Laboratories Agency (VLA) then gave a series of presentations to give the Group a better understanding of how the VLA’s work fits within Defra’s bTB research programme. Firstly, he gave an overview of disease trends to demonstrate how disease levels had changed over time. Dr Clifton-Hadley then outlined a case study where the VLA monitored the use of tuberculin produced at VLA Weybridge and at Lelystadt in the Netherlands to compare performance of the two products.
4. Dr Clifton-Hadley then outlined two research projects the VLA were undertaking. Firstly, he outlined a project which was designed to define potential indicators of ‘the problem TB herd’ based on duration of movement restrictions, herd size, number of reactors and past TB history etc. This project considered what diagnostic and prognostic decisions could be supported through a modeling approach both as a means of identifying herds at risk of being problem herds and then managing TB breakdowns in such herds.
5. Dr Clifton-Hadley then explained some of the work the VLA was doing on predictive modelling. They had used CTS data on animals, their locations and their movements to model and predict where bTB may appear.
6. The meeting then discussed Dr Clifton-Hadley’s presentations. The Group asked him what information he thought was missing from the CTS data that might help improve the results of this modelling work. Dr Clifton-Hadley suggested that it would be helpful if information on linked holdings could be included so that the data could capture all the movements within those multiple holdings.
7. Glyn Hewinson (VLA) then gave an overview of the work the VLA was doing on improvements to diagnostic testing. He began by explaining how an animal becomes infectious. Dr Hewinson then gave a broad overview of the use of the gamma interferon skin test. Although the meeting noted wider concerns over the use of gamma interferon, particularly because of the number of perceived false positives, Dr Hewinson explained the advantages of using gamma interferon: the detection of infection much earlier than the bTB skin test (and before visible lesions develop), lab-based analysis removed any subjectivity of interpreting test results and the test allows further protein inclusion which improves sensitivity and specificity. Defra is currently reviewing the use of gamma interferon in consultation with interested organisations.
8. Dr Hewinson then outlined ongoing research into the use of polymerase chain reaction (PCR) for cattle and badgers. The PCR technique can be used to detect the presence of DNA from the M.bovis in animal tissues, cultures of the organism or the environment. But this test still needs to be validated to allow discrimination between M. bovis and other closely related species of mycobacterium in environmental samples. Whilst it may be possible to identify areas, such as badger setts, where the organism is present it would not be possible to identify individual animals that were infected or know whether the DNA detected was from M. bovis mycobacteria that were viable and infectious. Before any test can be considered for use in TB control policy it is essential that it is robust and fully validated, so that its sensitivity and specificity (i.e. its ability to detect true positive and negative results) are known.
9. Dr Hewinson also gave an overview of the VLA’s work on vaccines. Defra is currently considering potential policy options for using cattle and badger vaccines in consultation with interested organisations.
10. Dr Robbie McDonald from the Central Science Laboratory (CSL) then gave the Group an overview of CSL’s work. The CSL collaborate with VLA, Defra and the devolved administrations. He then explained the work undertaken at CSL on distance sampling which was designed to estimate badger density and population within some of the RBCT areas. Dr McDonald then outlined a study which aims to estimate the frequency of badger visits into farm buildings. The Group was shown video footage of badgers inside farm buildings both in nose to nose contact with cattle and in their feed.
11. The Group asked whether there were any indications of what types of farmers have high badger activity. Dr McDonald responded that there was seasonal variation based on feed availability – more feed is available in winter. The distance between the buildings and the main sett were also a factor. The meeting then asked whether there were any plans to study activity in pasture. Dr McDonald replied not at present but it is something they could look into.
12. Dr Steve Carter then gave a presentation on the ecological considerations for badger vaccination. This presentation emphasised the importance of the social organisation of badgers and studies had been undertaken at Woodchester Park and in the vaccination study area on bait marking to allocate and map social groups. Dr Carter then gave a presentation on an ecological and epidemiological investigation of a badger population naturally infected with M.bovis at Woodchester Park. Risks of disease incidence correlated with individual and group-level dispersal. The percentage of TB superexcretors was higher in older badgers and TB excretor prevalence increased in unstable social groups.
13. Finally, the Group heard from Dr Graham Smith (CSL) who gave an overview of some of the CSL’s modelling work. Dr Smith explained how models could be used to explore and predict disease spread, levels of disease or the economic impacts of certain measures.
14. The Chairman then thanked the VLA and CSL for their time and very interesting presentations.
15. At the end of the presentations the Group had a round-up discussion. Following the earlier presentation on the gamma interferon blood test, the Group considered whether they could do more to help promote the benefits associated with gamma interferon: it picks up infection much earlier than the skin test, sometimes up to 6 months earlier before visible lesions develop. The Group decided to wait for the options and outputs from Defra’s review of gamma interferon later this year before it considered what input it might have in this area.
16. The Group also discussed linked holdings and Single Occupancy Authorities (SOAs). SOAs had been highlighted in the press recently as disease control risks because animals could be moved freely within a SOA across some distance. The earlier VLA presentation on predictive modelling had also suggested that movement data from linked holdings and SOAs would be useful in helping to predict disease areas.
17. When the Group produced its advice to Ministers on pre-movement testing in December 2006, one of its recommendations was that Defra and Animal Health urgently review the exemption of pre-movement testing for moves within SOAs because of the disease risk associated with these movements. The Group understands that SOAs are being reviewed as part of the implementation of the Madders Review of the Livestock Movement Controls Report, July 2006. The Group recognises that SOAs pose risks to many diseases, not just bTB, but it recommends that SOAs should be reviewed urgently using risk-based decisions. The Group would consider this further at its next meeting.
18. The Group believes both badger and cattle vaccines are worth considering to help reduce the risk of disease. It has offered comments on Defra’s policy options papers and it will be represented at Defra’s vaccines meeting with interested organisations on 3 April. The Group also supports the Environment, Food and Rural Affairs (EFRA) Committee’s recommendation that “the Government must continue to fund research into vaccines… on an invest to save basis”.
19. Lastly, the Group also supports the Efra Committee’s “surprise and concern that Defra has not yet initiated a cost-benefit analysis of the options based on cattle controls recommended by the ISG in order to inform its decisions on future policy on cattle TB”. The Group recommended that Government consider the costs and benefits of increased cattle controls as a priority when it wrote to Jeff Rooker of 16 October 2007.
Those present:
Peter Jinman (Chairman)
Brian Jennings
Bill Madders
James Kirkwood
Andrew Cunningham
Dr Richard Clifton-Hadley (VLA)
Dr Glyn Hewinson (VLA)
Dr Robbie McDonald (CSL)
Dr Steve Carter (CSL)
Dr Graham Smith (CSL)
Professor Quintin McKellar (Chairman, TB Science Advisory Body)
Rory Cooney (Secretary, TB Science Advisory Body)
Fiona Stuart, TB Programme, Defra
Teresa Filley, Defra, TB Advisory Group Secretary
29 April 2008
Page last modified: 6 May 2008