Bovine tuberculosis (TB) is a challenging disease to control and eradicate due to several factors. Ireland's bovine TB Eradication Programme operates in line with best national and international scientific research and advice. A large body of peer-reviewed research has been conducted into the spread of TB in Ireland and the risks underlying its transmission. This research has found that the principal causes of TB introduction and spread include:
• Movement of cattle with undetected infection.
• Residual infection in cattle previously exposed to TB.
• Spread across farm boundaries.
• Indirect spread through other biosecurity breaches, and/or
• Spread from infected badgers to cattle.
The relative contribution of each of these factors will vary from farm to farm. There is a wide variety of measures needed to reduce the levels of bovine TB which include reducing the risk of introducing infection to a herd from purchased or moved in cattle, reduce the risk of introduction to cattle from wildlife through measures such as fencing off badger setts and removing high risk animals such as those that have tested inconclusive previously or have been present at a breakdown previously over time, and curtailing the movement of high risk animals from high risk herds as set out in the TB action plan.
Ireland’s current TB Eradication Programme necessarily incorporates a wildlife strategy which includes the removal of badgers from areas where there has been a TB outbreak. Such a requirement arises as tuberculosis is present both in cattle and in badgers and both species share the same environment, and the same strains of TB. The current policy was introduced in response to research conducted over many years by my Department.
Supported by scientific research, the current bovine TB eradication strategy includes a combination of badger culling and vaccination depending on the circumstances. Badger vaccination is a key part of the Irish TB Eradication Programme. This follows over 15 years of research work using BCG vaccine to prevent tuberculosis infection in badgers, and scientific trials carried out between 2013 and 2017 that show that vaccination is no less effective than culling.
The evidence to support badger vaccination within the TB eradication scheme is being added to on an ongoing basis as additional research is published in peer reviewed scientific journals. My Department collaborated with University College Dublin and the University of Waginengen to validate the efficacy of vaccination in the field and to model where higher risks exist at a local farm level which will support better targeting of TB controls in future years.
My Department provides advice to farmers on how to reduce the risk of TB from wildlife which can be accessed at: [www.bovinetb.ie]
The Scientific Working Group of the TB Forum, which consists of scientific experts in the field, were asked to consider the sources of bovine TB in Ireland, including the role of badgers. Their detailed scientific report is available at the following link: https://assets.gov.ie/static/documents/sources-of-transmission-of-tb-for-cattle.pdf. Among their conclusions is the statement "There is strong evidence that badger-to-cattle transmission pathways contributes to TB in Ireland".
The main scientific veterinary publications underpinning this policy are listed below.
• Efficacy of badger culling
Badgers were first identified as being susceptible to infection with Mycobacterium bovis (M.bovis), the bacterium that causes bovine tuberculosis (bTB), during the 1970s. My Department funded research which concluded that badgers were likely to have been involved in the recycling of bTB in cattle and concluded that eradication of bTB from the national herd would not be feasible until TB in badgers was addressed and controlled.
Eves, J.A., 1993. The East Offaly Badger Research project: an interim report. The Badger. In: Proceedings of the Royal Irish Academy, Dublin, pp. 166–173.
Eves, J.A., 1999. Impact of badger removal on bovine tuberculosis in east County Offaly. Ir. Vet. J. 52, 199–203
O’Mairtin, D., Williams, D.H., Griffin, J.M., Dolan, L.A., Eves, J.A., 1998. The effect of a badger removal programme on the incidence of tuberculosis in an Irish cattle population. Prev. Vet. Med. 34, 47–56.
O’Mairtin, D., Williams, D.H., Dolan, L., Eves, J.A., Collins, J.D., 1998. The influence of selected herd factors and a badger-intervention tuberculosis-control programme on the risk of a herd-level trade restriction to a bovine population in Ireland. Prev. Vet. Med. 35, 79–90.
Griffin et al Griffin, J.M., More, S.J., Clegg, T.A., Collins, J.D., O’Boyle, I., Williams, D.H., Kelly, G.E., Costello, E., Sleeman, D.P., O’Shea, F., Duggan, M., Murphy, J., Lavin, D.P.T., 2005. Tuberculosis in cattle: the results of the four-area project. Irish Veterinary Journal 58, 629-636.
Griffin, J.M., Williams, D.H., Kelly, G.E., Clegg, T.A., O’Boyle, I., Collins, J.D., More, S.J., 2005. The impact of badger removal on the control of tuberculosis in cattle herds in Ireland. Preventive Veterinary Medicine 67, 237-266.
• Efficacy of badger vaccination
A field trial over 755 Km2 in Co. Kilkenny using the BCG vaccine and a blind placebo demonstrated that badger vaccination, with an efficacy of 60%, could lower the R value (reproductive ratio) of badger to badger TB spread from 1.22 to 0.5
Gormley, E., Ní Bhuachalla, D., O’Keeffe, J., Murphy, D., Aldwell, F.E., Fitzsimons, T., Stanley, P., Tratalos, J.A., McGrath, G., Fogarty, N., Kenny, K., More, S.J., Messam, L.McV., Corner, L.A.L., 2017. Oral vaccination of free-living badgers (Meles meles) with bacille Calmette Guérin (BCG) vaccine confers protection against tuberculosis.
Aznar, I., Frankena, K., More, S.J., O’Keeffe, J., McGrath, G., de Jong, M.C.M., 2018. Quantification of Mycobacterium bovis transmission in a badger vaccine field trial. Preventive Veterinary Medicine 149, 29-37
• Vaccination as a replacement for culling
The Non-Inferiority Trial was established in seven areas of the country over seven years, finishing in 2017. With the efficacy of BCG vaccination in reducing the spread of Mycobacterium Bovis between badgers proven in the Kilkenny trial, this trial sought to examine if vaccinating badgers would keep spread to cattle suppressed. A large part of a county was subject to badger vaccination and was compared to culling badgers (in response to TB breakdowns) in another similarly sized part of the county. While TB increased in some of the trial areas, the overall result of the trial was that badger vaccination was not inferior to badger culling in terms of spread to cattle.
Martin, S.W., O’Keeffe, J., Byrne, A.W., Rosen, L.E., White, P.W., McGrath, G., 2020. Is moving from targeted culling to BCG-vaccination of badgers (Meles meles) associated with an unacceptable increased incidence of cattle herd tuberculosis in the Republic of Ireland? A practical non-inferiority wildlife intervention study in the Republic of Ireland (2011-2017). Preventive Veterinary Medicine 179.