Test and Vaccinate or Remove (TVR) aims to control TB by vaccinating test-negative badgers and killing test-positive animals. The idea for this approach originated within the Welsh Government, which commissioned model simulations of TVR in 2009. On the basis of those simulations, the Welsh Government rejected TVR because the approach was considered too risky.

The model simulations predicted that TVR would reduce cattle TB incidence only if surviving badgers did not change their behaviour when test-positive animals were killed1. Unfortunately, evidence suggests that killing even small numbers of badgers prompts the survivors to range more widely, transmitting infection to other badgers and potentially to cattle2. TVR aims to halt disease transmission by removing both infected badgers (by culling) and those that can become infected (by vaccination). In practice, however, both infected and susceptible badgers will remain, because some animals evade capture, some infected animals test negative, and the vaccine fails to protect some animals. TB transmission can thus continue despite TVR, especially where badger behaviour is disrupted. For this reason, modelling predicted that TVR would increase cattle TB if it altered badger behaviour1. Hence, although TVR is an intuitively appealing approach to TB control, it is a risky one. Moreover, the process of capturing, immobilising, blood sampling and testing badgers is very labour-intensive and hence costly.

A subsequent modification of the Wales TVR model, commissioned by DARD NI, suggested that the harmful effects of TVR might be overcome by conducting more than one round of trapping each year3. However, this model appears to have simulated changes in badger behaviour in a way that was different (and less realistic than) that in the Welsh model. Therefore, the predictions of the NI model may be optimistic.

Anne Brummer

Save Me Trust 

References:

1 FERA. Badger Control Model for Wales – Trap-Test-Cull-Vaccinate Supplemental Report – 4th March 2009. (Welsh Government, 2009).

2 Bielby, J., Donnelly, C. A., Pope, L. C., Burke, T. & Woodroffe, R. Badger responses to small-scale culling may compromise targeted control of bovine tuberculosis. Proceedings of the National Academy of Sciences of the United States of America 111, 9193-9198, doi:10.1073/pnas.1401503111 (2014).

3 Smith, G. C., Budgey, R. & Delahay, R. J. A simulation model to support a study of test and vaccinate or remove (TVR) in Northern Ireland. (Department of Agriculture and Rural Development, Stormont, 2013).