Vaccination will be an important tool to help control bovine TB in the future.
But the evidence suggests it will not work on its own – and where both cattle and badgers are concerned, a realistic programme remains a number of years away.
Vaccination won’t work on an animal that already has bovine TB, and no country in the world where wildlife carries the disease has eradicated it in cattle without tackling it in wildlife too.Vaccination and cows
There are calls for cows to be vaccinated against bTB.
However there is no legal vaccine available. Currently the only option is the BCG vaccine (Mycobacterium bovis Bacille Calmette-Guérin – ref 1,2,3,4,5).
The problem is that at present it is impossible to distinguish between a BCG-vaccinated and TB-infected cow. And for this reason it is currently illegal under EU law to vaccinate cattle with the BCG jab.
Work is underway to devise a DIVA test (ref 6,7,8) - a test that can Differentiate between Infected and Vaccinated Animals. But even when this has been fully developed, it will need to go through EU and international approval.
The upshot is that most estimates say it will be ten years before vaccinating cattle is a realistic possibility (9).
On top of that, there's evidence to suggest that the BCG vaccine and DIVA test will not eradicate bovine TB on their own. A recent scientific study (10) concluded that the efficacy of the BCG vaccine in cattle was between 56% and 68%.
We know the BCG vaccination reduces the progression, severity and excretion of TB, resulting in reduced transmission between animals, but it is not perfect. And for any vaccine to eradicate a disease it is necessary to ensure that 80% of the target population are immunised. The current BCG vaccine just does not does not shape up.
Scientists have said that vaccination has to be used in combination with other measures, which must include dealing with the disease in badgers. You can read more about bovine TB and vaccination on the Defra site, here.
Field trials of a cattle vaccine and associated DIVA test are due to start in the UK in 2014.
Why isn’t a vaccine being used to protect badgers?
Most voices in the debate, including the NFU, fully support the development of vaccines for badgers.
However, the only vaccine available is an injectable form – and that presents problems.
You need to cage-trap the badgers to vaccinate them. And you have to it annually for period of at least five years.
The process is costly and needs to be carried out by people who have been on accredited courses. Every trap will have to be visited early in the morning, every day.
In January 2013, the Welsh Assembly completed its first year vaccinating badgers in the Pembrokeshire hotspot area. Costs per badger are likely to run to £662 per year for five years – a total of £3,310 per badger (11).
And here too, there are still question marks over the efficacy of the vaccine.
It will not cure a sick badger, one which is already infected with TB.
The science suggests the vaccine is most effective in very young animals, and less so in older subjects (12). Young badgers spend their early weeks in the sett, making it impossible to trap and vaccinate them and putting them at risk of infection before they emerge.
There is also no evidence as yet which shows that vaccinating a proportion of the badger population actually results in a reduced risk to cattle.
An oral bait vaccine is likely to offer the most successful route forwards. But this option is still some years away from becoming a part of any badger control plan, because there is no licensed or proven oral vaccine currently available.
(1) Wedlock D.N., Denis M., Vordermeier H.M., Hewinson R.G., Buddle B.M. (2007). Vaccination of cattle with Danish and Pasteur strains of Mycobacterium bovis BCG induce different levels of IFN gamma post-vaccination, but induce similar levels of protection against bovine tuberculosis. Vet Immunol Immunopathol. 118, 50-8.
(2) Wedlock D.N., Aldwell F.E., Vordermeier H.M., Hewinson R.G., Buddle B.M. 2011. Protection against bovine tuberculosis induced by oral vaccination of cattle with Mycobacterium bovis BCG is not enhanced by co-administration of mycobacterial protein vaccines. Vet Immunol Immunopathol.144(3-4):220-7. Epub 2011 Sep 29.
(3) Buddle, B.M.,Wilson, T., Aldwell, F.E., de Lisle, G.W., Vordermeier, H.M., Hewinson, R.G., Wedlock, D.N. 2011. Low oral BCG doses fail to protect cattle against an experimental challenge with Mycobacterium bovis. Tuberculosis 91: 400-405.
(4) Vordermeier H.M., Villarreal-Ramos B., Cockle P.J., McAulay M., Rhodes S.G., Thacker T., Gilbert S.C., McShane H., Hill A.V., Xing Z., Hewinson R.G. 2009. Viral booster vaccines improve Mycobacterium bovis BCG-induced protection against bovine tuberculosis. Infect Immun. .Aug;77(8):3364-73. Epub 2009 Jun 1. Erratum in: Infect Immun. 2011 May;79(5):2134.
(5) Hope J.C., Thom M.L., McAulay M., Mead E., Vordermeier H.M., Clifford D., Hewinson R.G., Villarreal-Ramos B. 2011. Identification of surrogates and correlates of protection in protective immunity against Mycobacterium bovis infection induced in neonatal calves by vaccination with M. bovis BCG Pasteur and M. bovis BCG Danish. Clin Vaccine Immunol. 2011 Mar
(6) Whelan A.O., Clifford D., Upadhyay B., Breadon E.L., McNair J., Hewinson G.R., Vordermeier H.M. 2010. Development of a skin test for bovine tuberculosis for differentiating infected from vaccinated animals. J. Clin. Micro. 48, 3716-3181.
(7) Vordermeier M., Gordon S.V., Hewinson R.G. 2011a. Mycobacterium bovis antigens for the differential diagnosis of vaccinated and infected cattle. Vet Microbiol 151(1-2):8-13.
(8) Vordermeier M., Jones G.J., Whelan A.O. 2011b. DIVA reagents for bovine tuberculosis vaccines in cattle. 2011b. Expert Rev Vaccines.
(9) Letter, EU health commissioner Tonio Borg, Jan 2013
(10) Field Evaluation of the Efficacy of Mycobacterium bovisBacillus Calmette-Gue´rin against Bovine Tuberculosis in Neonatal Calves in Ethiopia. Gobena Ameni, Martin Vordermeier, Abraham Aseffa, Douglas B. Young and R. Glyn Hewinson.
(11) Intensive Action Area Badger Vaccination Report - Year 1, Welsh Assembly Government, Jan 2013
(12) Bacillus Calmette-Gue´ rin vaccination reduces the severity and progression of tuberculosis in badgers (published Dec 1 2012). Mark A. Chambers, Fiona Rogers, Richard J. Delahay, Sandrine Lesellier, Roland Ashford, Deanna Dalley, Sonya Gowtage, Dipesh Dave, Si Palmer, Jacky Brewer, Timothy Crawshaw, Richard Clifton-Hadley, Steve Carter, Chris Cheeseman, Chris Hanks, Alistair Murray, Kate Palphramand, Stephane Pietravalle, Graham C. Smith, Alexandra Tomlinson, Neil J. Walker, Gavin J. Wilson, Leigh A. L. Corner, Stephen P. Rushton, Mark D. F. Shirley, George Gettinby, Robbie A. McDonald and R. Glyn Hewinson