Last week we reported on the latest published research results coming out of DAERA’s Test, Vaccinate or Remove (TVR) badger TB study, conducted in a 100km2 area of Co Down over five years between 2014 and 2018.

The data presented show that the TB incidence rate of captured badgers fell from around 14% at the start of the study, to just 1.9% in the fifth and final year of the project. The authors conclude that a TVR approach can significantly reduce TB rates in badgers, and suggest that it could be considered in future TB control strategies.

In principle, TVR seems like an ideal strategy, with badgers trapped in cages, tested for TB, infected animals euthanised, and healthy animals vaccinated and released.

But is it really an approach that farmers can accept, given that the inevitable trade-off for DAERA beginning wildlife intervention work is cuts to compensation for TB reactors and tougher controls around animal movement?

There are a number of issues to consider:

  • A TVR approach is labour-intensive. The fifth year of the project involved 26 DAERA field staff, who managed to capture 781 badgers over the period from 18 June to 18 October. Of these 781 badgers, many were caught multiple times, so there were only 341 unique capture events.
  • TVR is expensive. While there were additional costs as this was a research project, delivery cost £836,000 in the final year (2018) and a total of £4.5m over the five-year period.
  • Only a fraction of badgers were caught. Estimates suggest that there are 3.88 badgers per km2, or 3,880 animals across the entire 100km2 TVR area in Co Down. On that basis, DAERA only managed to trap 9% of the badger population in the area in 2018.
  • Few badgers are culled. In the first year that DAERA culled infected badgers (year two of the study), 11.4% of badgers recorded a positive test, so just 40 badgers were due to be culled. By 2018, only 1.9% of badgers tested positive for TB across the period from June to October, suggesting that just six badgers were culled.
  • The test misses positives. The badger TB test used in the field (dual path platform – DPP) has a high specificity (probability that an uninfected animal will test negative) of around 97%, but a sensitivity (probability that an infected animal will test positive) of around 70%. It is not much better than the current skin test used in cattle.
  • Fewer cattle have TB. While TVR did significantly reduce TB rates in badgers, an incidence rate of 1.9% is still significantly more than the individual animal incidence rate for cattle, which currently stands at 0.75%.
  • The last major survey of the badger population in NI was in 2007-2008. It estimated there were 33,500 animals, but allowing for error in the data, the actual number could be between 26,000 and 41,200.

    The 33,500 figure equates to a population of 2.5 badgers per km2, which is thought to be twice that of the Republic of Ireland (ROI). In drumlin farmland in NI, the population is estimated at closer to five per km2.

    With the latest analysis of roadkill data suggesting that 17.1% of badgers across NI have TB (likely to be an underestimate as the badgers are only assessed for visible lesions), then there could be approximately 5,700 animals infected with bovine TB at any one time.

    If, for example, DAERA “rolled out” TVR in three 100km2 areas of NI as part of new wildlife intervention work, and replicated the results it achieved in Co Down, we are looking at less than 200 infected badgers being culled every year.

    TBEP

    Perhaps then it should be no surprise that the TB Eradication Partnership (TBEP) group, the expert body currently advising DAERA on a new TB strategy has not recommended a TVR approach.

    Instead, it continues to argue that DAERA should replicate the model from the Republic of Ireland (ROI) where culling of badgers in TB hotspot areas has reduced TB prevalence in both badgers and cattle. With lower infection rates, ROI is now able to move towards vaccination of badgers as the main control policy.

    The predecessor to the TBEP, the TB Strategic Partnership Group, also made a similar recommendation to DAERA in 2016.

    Read more

    TVR cuts badger TB sevenfold

    Badger vaccination key in TB eradication end game – Department