Can bovine TB be eradicated from the Republic of Ireland? Could this be achieved by 2030?

Abstract

Background: There has been an ongoing decline in bovine tuberculosis (TB) in the Republic of Ireland, however, TB has yet to be eradicated. Further to a recent commitment by the Irish government to eradicate TB by 2030, this paper considers two questions, 'Can bovine TB be eradicated from the Republic of Ireland?' and 'Could this be achieved by 2030?', given current knowledge from research.

Main body of the abstract: Until very recently, Ireland has lacked key tools required for eradication. This gap has substantially been filled with the national roll-out of badger vaccination. Nonetheless, there is robust evidence, drawn from general national research, international experiences, and results of a recent modelling study, to suggest that all current strategies plus badger vaccination will not be sufficient to successfully eradicate TB from Ireland by 2030. We face a critical decision point in the programme, specifically the scope and intensity of control measures from this point forward. Adequate information is available, both from research and international experience, to indicate that these additional measures should broadly focus on adequately addressing TB risks from wildlife, implementing additional risk-based cattle controls, and enhancing industry engagement. These three areas are considered in some detail.

Conclusion: Based on current knowledge, it will not be possible to eradicate TB by 2030 with current control strategies plus national badger vaccination. Additional measures will be needed if Ireland is to eradicate TB within a reasonable time frame. Decisions made now will have long-term implications both in terms of time-to-eradication and cumulative programme costs.

Keywords: Bovine tuberculosis; Constraints; Eradication; Industry engagement; Ireland; Risk-based cattle controls; Wildlife risks.

Fig. 1

The annual number of TB reactors in Ireland, from 1959 (when records are first available) to 2018, including magnification of the period from 2000 to 2018

Fig. 2

Estimated total number of herds infected with bovine viral diarrhoea (BVD) virus (y-axis, log scale) in Ireland in the years following the start of the compulsory national BVD eradication programme, under differing levels of retention of persistently infected (PI) animals. Output of the Irish BVD model (FarmNet 1.0) as of 2015. For modelling details see Thulke et al. [22] or http://www.ecoepi.eu/FarmNet-BVD/. In particular note: The green line (TagRetNone): the predicted fall in total PI numbers assuming all PIs are removed from farms immediately following testing (that is, without any PI retention). Under this scenario, estimated time to eradication is 3–4 years from programme start (2016–17). The yellow line (TagRetUnlim): predicted fall in PI numbers given high levels of PI retention (that is, PI retention continues at a high level each year). Under this scenario, eradication is unlikely to occur. The black line (TagRetLim, generally obscured by the light blue line): the predicted fall in PI numbers, assuming high levels of PI retention during the first three years of the programme, but no PI retention subsequently. Under this scenario, estimated time to eradication is 6–7 years from programme start (2019–20). Three additional lines were included to test sensitivity assumptions, including: the red line (TagRetHighInf, doubling of transmission probabilities), the purple line (TagRetLowMort, doubling of survival time of PI animals) and the light blue line (TagRetNoIU, suppression of movement of animals with in utero infections)

Fig. 3

Screenshot of cattle movement events in Ireland, in this case from 12 August 2016. From McGrath et al. [50]. The blue lines depict movements to slaughter or export, and the red lines from farm to farm including via a mart. The movement video is available on YouTube at https://youtu.be/PTCdPMnenBw