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DIVA skin test reagent and OIE bovine tuberculin international standard - SE3312

Policy relevance: The development of improved vaccines for cattle forms part of the Government’s comprehensive eradication strategy for bTB. To enable BCG vaccination to be used alongside conventional test and slaughter control policy, a BCG compatible DIVA test is required. A DIVA skin test (DST) reagent based on recombinant proteins of antigens not recognised by animals vaccinated with BCG has been developed. A data gap analysis has highlighted a level of uncertainty in the estimate of test sensitivity in detecting BCG-vaccinated animals not protected from bTB following experimental infection with M. bovis. The proposal described herein will address this data gap. The Bovine Tuberculin International Standard is required by manufactures of bovine tuberculin for quality assessment of their product. Due to the declining stocks of the international standard, a replacement standard is required. The proposal described herein evaluating two candidiate replacements will generate data to support the selection of a new international standard. This work will ensure that the tuberculin used as part of test and slaughter strategies will be produced to a unifofm quality for the next 20 years. Project summary: In this proposal we detail the work that is required to improve the precision in the estimate of the relative sensitivity of the DST in identifying BCG-vaccinated animals not protected from bTB following infection with M. bovis. To do so, we plan to conduct two BCG-vaccination / M. bovis experimental infection experiments at APHA Weybridge. In addition, a third vaccination / infection experiment will be conducted in New Zealand under sub-contract with AgResearch. Data will be collected on the performance of the DST and all animals will undergo a detailed post mortem analysis to identify animals where BCG vaccination failed to protect from bTB. In this way, we will increase the numbers of animals in the key target group (i.e. BCG vaccinated animals not protected from bTB) that have been tested with the DST. We expect that the addition of the data generated from these experiments to our existing data set will increase the precision in the estimate of the relative sensitivity of the DST in these animals (as evidenced by a reduction in width of the confidence intervals for the sensitivity estimate). In this proposal we detail the work required to generate data on two new candidate bovine tuberculin preperations to support the decision of which to take further as the new Bovine Tuberculin International Standard. An OIE expert panel has appointed APHA to a consortium as the lead coordinator of cattle experiments being performed in 12 countries including GB. Furthermore, APHA will test the tuberculins in cattle experimentally infected with M. bovis. Each tuberculin candidate, as well as the existing international standard, will be tested at two different concentrations. The data generated at APHA will be submitted to consortium members at the Central Veterinary Institute (Lelystad) where it will be combined with data from other partners for the determination of potency.
There are two specific aims for this proposal.
Objective 1: Generate DST-F test performance data in BCG-vaccinated animals that fail to be fully protected from bTB following M. bovis infection.
Objective 2. Generate data to support the development of a new OIE international standard for bovine tuberculin
Time-Scale and Cost
From: 2019

To: 2021

Cost: £1,806,709
Contractor / Funded Organisations
APHA (Animal and Plant Health Agency)