Cattle TB history

Tuberculosis of cattle in the UK was relatively rapidly controlled following the decision to become officially TB free (99.8% of herds and 99.9% of cattle testing free of disease) in the middle of the last century, which saw the introduction of attestation. This involved testing, culling and restricting movement of infected cattle herds, which is the model across the entire developed world for control of bovine TB. However it was noted in the 1960’s that cattle TB was persisting in some areas of the South West of England, whereas the rest of the UK saw TB virtually completely eradicated in cattle.

Veterinary surgeons at the time hypothesised that a reservoir of infection must exist and consequently many wildlife species were examined, particularly in the TB hotspots. It was determined in the 1970’s that the badger was a significant reservoir of infection and also that there were high sett densities and badger disease prevalence in the areas where cattle measures were failing to eradicate the disease in cattle. In areas where cattle TB was successfully controlled badger disease was very low or nonexistent, based on studies of many thousands of road killed badgers. Other than deer, most other species did not appear to have sufficient disease susceptibility to act as reservoir hosts for TB.

During the 1970’s various badger culling exercises were undertaken in an attempt to control the disease, predominantly in the South West of England. Repeated gassing of setts was the most effective culling method, but this was banned in 1982 (it was deemed inhumane) and was followed by various less effective strategies involving trapping and shooting. It’s important to understand that gassing of setts (mainly with hydrogen cyanide) had been commonplace around the UK and was considered a normal part of the management of wildlife. Consequently the badger population was kept relatively low compared to today. Other factors such as maize silage (anecdotally) may have contributed to the subsequent rise in the badger population too.

The badger had been protected to a degree in 1973 in an Act that was aimed at preventing cruel practices known as ‘badger baiting’. However, farmers and countrymen did use other legal methods to control the badger population before and after this Act. In 1992 the Protection of Badgers Act came into force which fully prevented any interference with badgers or their setts. Although the potential for licensing to cull to prevent livestock disease is in the act, these were generally not awarded, other than for a handful of now very paltry government attempts to control remaining TB hotspot areas.

In the mid 1990’s TB rose sharply, particularly in the South West of England. Despite the fact that every effectively delivered badger cull always reduced cattle TB the whole issue of badger culling became highly politicised and in 1996 Professor Krebs was invited to report on the history to date and include recommendations to government for the future.

Although the more aggressive/ effective badger cull efforts pre 1996 were acknowledged by Prof Krebs to have been highly effective against TB in cattle, he decided that they hadn’t been conducted as a true scientific controlled experiment. They were also the subject of much public controversy and hence he advised the government to conduct a large 5 year multi-site randomised controlled study into the effectiveness of badger culling on the incidence of cattle TB, rather than to revert to an aggressive badger removal strategy there and then before things escalated further.

Many academics deny the relevance of the outcomes of extensive badger cull operations such as Thornbury, where cattle TB reduced to zero for ten years following complete badger removal of the area. In fact they refer to them as ‘non-scientific’. It is not uncommon for academics to conclude ‘More research is needed . . .’ despite what appears to the onlooker as common sense. It would be interesting to see the total spend by government on TB research since the Krebs report.

The Randomised Badger Culling Trial (RBCT)

The Independent Scientific Group (ISG) were formed and chaired by Prof John Bourne in 1998 to design and implement the trial, known as the Randomised Badger Culling Trial or RBCT. The trial consisted of 11 areas split into 3 groups of behaviours: proactive culling, reactive culling and no culling (as a control area). Reactive culling was abandoned early as this was felt to be causing increased TB.

Although the initial trial design (ISG first report 1998) described proactive cull areas as:

‘The target would be to cull as large a proportion of badgers resident within the treatment area as possible, and to prevent recolonization by further culling on a regular basis’.

This was watered down by the new Labour government ministers, who used an interpretation of the Bern convention to set a maximum cull effort of 70% of the population in the area, thus compromising the effectiveness of the cull, even if performed maximally to meet this new 70% target. There were many critics of the cull effectiveness of the RBCT, which was also hampered by an outbreak of Foot and Mouth Disease in 2001, and continually disrupted by animal rights activists.

The ISG drew their conclusions relatively early from a long term disease control point of view and stated in 2007 that ‘. . . badger culling cannot meaningfully contribute to the future control of cattle TB in Britain’. However this should have read ‘. . . badger culling, as performed in the RBCT, cannot . . .’. This conclusion was reached before the true long term effects of the cull had had chance to fully materialise, which takes several years.

One of the main reasons behind their conclusion was the finding of what has been called ‘the perturbation effect’ which they claim to be due to infected badgers dispersing from cull areas, and general social group disruption, that results in spread outward of TB in the badger population creating a detrimental effect (rise in cattle TB) immediately outside the cull zone. However within the RBCT proactive cull zones, despite the relatively poor cull effort, TB in cattle reduced for at least 10 years post culling. 

The perturbation effect itself has been the subject of some controversy partly because the effect of human relocation of badgers during the RBCT could not be measured with any certainty. It was admitted during Parliamentary Questions by Mr Bradshaw that there was a high rate of trap disruption and/or theft (around two thirds of traps) during the cull operations. It seems likely that this would involve some level of badger removal/relocation by the saboteurs. The perturbation effect from culling is yet to be observed anywhere outside of the RBCT in other badger cull zones, to my knowledge.

Current government policy on badger culling

Although the RBCT was designed to end the controversy surrounding badger culling it seems to have increased it. Having had time to review the longer term effects of the RBCT and to consider methods to reduce the perturbation effect, the current stance of the government is to grant licenses for badger culling when very strict criteria can be met regarding efficiency, safety and humaneness of culling method. The license conditions contain measures to reduce the possibility of any perturbation effects by using large areas, hard boundaries and high culling rates.

Two pilot study areas to assess a methodology of conducting badger culling using controlled shooting were set up with a view to satisfying the license criteria from these three important aspects. More importantly this level of detailed approach would be required to counter the certain Judicial Review that would be demanded by the Badger Trust to attempt to prevent any culling taking place. Without the risk of this Judicial Review, licensed culling may well have gone on with much less cost and delay. The government appointed an Independent Expert Panel to oversee and assess year 1 of the pilot studies, whose conclusion was that the culls had failed to meet the targets set. An extension was granted in year 1 to allow the cull operators to increase the effectiveness of the cull (and consequently reduce the risk of disease) and recommendations from the IEP were carried forward to subsequent years to improve the performance of the cull effort. 

These pilots were subjected to heavy disruption from protesters but it was shown that using a combination of controlled shooting and cage trapping that this methodology could be used to the satisfaction of the Chief Veterinary Officer and Natural England, particularly where interference with the cull effort was policed effectively. 

The pilots were deemed to be very costly, but the overwhelming element of the cost was not related directly to the culling of badgers per se. It was heavily weighted to the policing to control protesters and to actually design and study what was going on rather than the cost of simply undertaking it. It is rare for these costs to be publicly broken down accurately. The government are now keen to encourage more areas of the UK to apply for licenses to create cull zones, albeit with sufficient professionalism to satisfy Natural England’s licensing criteria. This will require farmers to work together to create their own zones that meet the relevant license criteria.

Geography of TB in England

Figure 5 from the Krebs report shows how few persistent TB breakdown cattle farms there were in the decade before 1997, but also how persistent repeat infection on farms was starting to increase in the known infected areas of the UK, particularly following the Protection of Badgers Act (1992). Figure 6 from the ISG report shows how TB has radiated from original hotspots very slowly, rather than being spread universally across the UK.

Today England is split into 3 regions, known as the high risk area (HRA), low risk area (LRA) and the Edge area. In the LRA persistent recurring TB outbreaks on farm are extremely rare. This phenomenon predominantly occurs in the HRA. Following the FMD 2001 outbreak Cumbria (in the LRA) had bovine TB seeded in cattle farms due to repopulation from TB infected cattle areas. Devon (in the HRA), similarly struck by FMD, also had post-FMD repopulation and also had TB infection in cattle. However, standard cattle control measures applied in Cumbria reduced TB in that county rapidly such that despite its high cattle population and movements it still today has very low TB incidence in cattle. Figure 7 shows a post-FMD comparison of the two counties. There are far more stringent cattle measures occurring in Devon, due to the TB levels, than Cumbria, but to no good effect.

Figure 8 shows the steady rise of TB in each of the areas of the UK according to their current allocation to HRA, LRA etc.

Interestingly the more highly infected areas (particularly HRA and Wales), when viewed in this long term way, show parallelism to rises and falls of cattle infection, despite being geographically distinct. It suggests a common background reason for the infection rates to rise and fall together over the years in these areas for reasons unrelated to their individual TB policy. It may be that this parallel fluctuating rise and fall of cattle TB reflects the level of infection or the population dynamics of the badger, which may itself relate to the severity of winters or other such factors.

These slow multi-year fluctuations also show the danger in analysing alterations in TB infection status of geographical areas over short timescales (less than 10 years). TB fluctuates up and down from year to year, but in highly infected areas steadily rises through the decades. In areas with minimal wildlife infection (Scotland and the LRA) TB is controlled perfectly adequately (as shown above) using relatively ordinary cattle measures akin to most of the rest of the developed world, where wildlife infections and/or population densities of these reservoir species are controlled. The risk to these low risk areas of the UK increases constantly as we allow the infection in the HRA to increase unabated, as this increases the opportunity of trans-locating infection into the LRA through cattle movements. The LRA is also at risk because nothing appropriate is being done to stop the steady outward radiation of background wildlife infection. Currently trans-located, cattle movement based infections in the LRA rarely result in long term breakdowns as seen in the HRA. This is likely to be because LRA badgers are currently relatively uninfected and/or have lower population densities, which means cattle measures (test/cull/restrict movement etc.) are able to work.

Cheshire is in the so-called ‘edge area’. In 2014, 102 road kill badgers from Cheshire were examined by Liverpool University laboratories, and a quarter of them were found to be positive for TB. This is around a 100- fold increase in the prevalence of badger TB compared to the last major study of Cheshire badgers.

Badger vaccination

All the studies into badger vaccination have shown that the vaccine is unable to prevent all vaccinated badgers from becoming infected. It also has shown that it fails to reduce the prevalence of TB infection in vaccinated badgers when compared to unvaccinated, as detailed in Figure 9. Note also the high proportion of infected badgers in this study of wild UK badgers both at the start and end of the study period, as detailed in this graph, displaying data from the largest published study of vaccination of wild badgers (Carter et al, 2012).

It has been shown that BCG vaccination can reduce the severity of TB in badgers and slow the progression of disease, but nevertheless they still become infected. Consequently it is likely that following the cessation of any vaccination program in infected badger populations, residual infection will remain and result in the future population becoming more infected again. This is exacerbated by the fact that we are only able to vaccinate around 70% of the targeted population with current methods and it is unclear if there would be sufficient manpower or vaccine to roll this out more widely. It is also unclear when, if ever, it would be appropriate to stop vaccinating if this option was deemed to be beneficial.

Wales has an area known as the Intensive Action Area (IAA) where badger vaccination is the method of choice for control of wildlife infection. This was to be a 5 year plan, and 4 years have been completed. The cost of vaccinating this area, which is 1.4% of Wales, is just under £1m per year, but the delivery of the vaccination effort has been highly effective in relative terms (>70%). Given the constraints of BCG mentioned above there will be residual infected badgers at the end of the 5 years, and newly born unvaccinated cubs arriving every year following the cessation of this program. Therefore it is highly unlikely that this short term program will result in any long term benefit to badgers or cows, albeit we may learn something of the feasibility of badger vaccine as a component of TB control in wildlife and/or cattle.

In the IAA there are also much more stringent cattle measures and general attempts in terms of biosecurity on farms aimed at controlling TB. This is not dissimilar to historical efforts (albeit not well documented) that occurred in the South West of England, and in Ireland, that completely failed because of the wildlife reservoir of infection that resulted in the persistence of disease as noted in all of the government reports on the subject since 1980. In Ireland the badger population density and TB infection rate is much lower following their culling program, and they are more hopeful, because of this, that badger vaccination will have a better chance of being a feasible component of TB control.

Throughout the UK there is likely to be illegal culling of badgers at some level, and this complicates the entire interpretation of the outcomes of policy, as it is not measured by anybody. The evidence does suggest that piecemeal small scale efforts at badger culling will make TB worse. This should be discouraged in favour of appropriately delivered, legal and effective licensed culling if we want to make progress against TB in the UK. Farmers need to work with the government to make sure the best outcomes are achieved for both our livestock and wildlife. We owe it to the future UK badger population to reduce their disease levels, even if this means we manage a healthier population dynamic for the species, through controlling population density and targeted removal of diseased social groups, as is the case with many TB reservoir host species around the world.

Summary

In the absence of wildlife infection existing cattle measures (skin testing, movement restriction and culling of infected cattle etc.) work very well across the world at controlling TB and this includes the non-wildlife-infected areas of the UK.

Cattle measures worked across almost all of the UK during a time when it was permissible to limit the badger population and particularly their interaction with cattle (pre 1992).

Every effectively conducted cull of badgers in the UK has resulted in lowered cattle TB, and this lowering of TB rises with the effectiveness of the cull effort (Krebs report, 1997).

Any efforts to control badger populations should be within the law under license and this is correct to reduce the potential risks suggested by the perturbation effect.

In published studies of infected badger populations BCG vaccination has failed to reduce the prevalence of infection in vaccinated badger populations compared to unvaccinated.

If we were in a position to reduce the badger population and its infection level sufficiently then badger vaccination may become more feasible as a part of the control strategy, but only if sufficient vaccine and an appropriate delivery method is available.

Unlawful ineffective badger culling has the potential to increase TB spread.

References

www.bovinetb.info – recommended for well referenced material and the source of some of the graphics used above (with permission).

Key Historical Government reports: ‘Badgers, Cattle and Tuberculosis’ – (Zuckerman, 1980) ‘Badgers and Bovine Tuberculosis – a review of policy’ (Dunnet 1986) ‘Bovine Tuberculosis in Cattle and Badgers’ – (Krebs, 1997) ‘Bovine Tuberculosis in Cattle and Badgers’ – (King, 2007)

Badger vaccination: BCG Vaccination Reduces Risk of Tuberculosis Infection in Vaccinated Badgers and Unvaccinated Badger Cubs (Carter et al, 2012 – see table S5 available on the online ‘plosone’ version of the paper for prevalence data) Wales Intensive Action Area – reports available on the Welsh Government website Cheshire Badgers – Prof Bennett (unpublished data – 2014 study at Liverpool University)