In 2007 the Independent Scientific Group (ISG) reported to the UK government the impact on bovine tuberculosis (TB) in cattle of a trial where badgers were culled between 1998 and 2005. This trial, known as the Randomised Badger Culling Trial (RBCT), was performed across 100 km2 (nominal) zones in the West of England. The results were based on a model of new herd incidence data. It was concluded that reactive culling generated overall detrimental effects, while proactive culling achieved very modest overall benefits at the cost of elevated incidence on neighbouring farms.
This work looks at more extensive RBCT data to examine if these findings hold true. Instead of presenting the results of a model, this work directly illustrates data supplied in March 2016 by the Animal and Plant Health Agency. Such data covers a greater number of years (1986 to 2012) and includes the prevalence of herd restrictions as well as herd incidence.
It appears that whilst cattle TB noticeably reduced in areas subjected to proactive culling, TB did not significantly increase in the surrounding areas. The more limited reactive culls were found to have no significant impact either positively or negatively. This applied to both the treated and surrounding areas.
The more extensive data also showed that culling badgers only reduced confirmed TB with no significant impact on unconfirmed TB. This was also found by the ISG in 2007 when using their model.
The delay before culling benefit became apparent was about 5 years after the first substantial cull. This has implications for the culls which started in South West England in 2013. If account is taken for the need to average the data, the number of years needed to see TB drop, and the reporting delay, it may not be until September 2023 before the impact of these culls become clear. Also, if culls stop after year four in each zone, this risks benefits falling short of those achieved in the RBCT.
Bovine tuberculosis in cattle from 1986 to 2012 in and around badger-culled areas of the RBCT