Badgers and bTB - Q&A

Badger - Neil AldridgeBadger - Neil Aldridge

What is bovine TB?

Bovine tuberculosis (bTB) is a highly infectious respiratory disease of cattle.  It is caused by the bacterium Mycobacterium bovis, which forms lesions (or 'tubercules') most often in the lungs.  M. bovis can also infect and cause TB in a wide range of other mammalian species.

Since the mid-1980s, the incidence of bTB in cattle has increased substantially; not just in the south-west of England but also in Wales and the Midlands. This represents an economic burden on the taxpayer and the farming industry, as infected cattle must be culled.

Do badgers infect cattle with bTB?

bTB is transmitted within and between populations of badgers and cattle but little is known about how transmission actually occurs.  The scientific evidence suggests that cattle can get bTB from direct or indirect contact with badgers, or other wild animals (and vice versa).  It is not known what proportion of bTB in cattle arises from badgers but the most recent study suggests that around 50% of outbreaks are related to badgers.  However, the proportion of outbreaks caused directly by badgers is much lower (5.7%), with these initial infections amplified by cattle-to-cattle transmission.  The complex biology of the pathogen and its mode of transmission make the study of bTB epidemiology particularly challenging.

Do other animals, such as deer, also get bTB?

Yes. Mycobacterium bovis can also infect and cause bTB in deer, goats, pigs, camelids (llamas and alpacas), dogs and cats, as well as many other mammals.

Do badgers die of TB?

Government research into badger ecology and TB epidemiology has been underway at Woodchester Park, Gloucestershire since the 1970s.  This has shown that TB is not a major cause of death in badgers.  Generally, infected badgers do not show any sign of infection and can survive for many years.  Badgers suffering from advanced stage bTB become severely emaciated and at this stage they can potentially shed live bacilli, and are therefore infectious.  More than 5,000 badgers have been vaccinated by the Welsh Government's badger vaccination programme, and none of these have shown any sign of ill health.  On balance, most badgers will live for five to six years in the wild.

What is the current conservation status of the badger in the UK?

Badgers are one of only a handful of large native mammals left in the UK. They are not an endangered species but are protected by national and international law, and are an important part of our biodiversity.

Badgers and their setts are protected under the Protection of Badgers Act 1992, which makes it illegal to kill, injure or take badgers or to interfere with a badger sett.  Badgers are also protected by the Convention on the Conservation of European Wildlife and Natural Habitats (known as the Bern Convention).

Importantly, the UK has 25% of the global population of the Eurasian badger Meles meles. We therefore have an international responsibility to conserve the species, and that includes protecting the range of genetic variation within the UK population.

Isn’t the population out of control because there are no natural predators for badgers?

The UK badger population is estimated to be around 400,000 although there are no up to date figures. The ecology and behaviour of badgers makes them very difficult to count and so the only national surveys that have been undertaken have estimated the number of setts, rather than the number of badgers.

There have only been three national badger sett surveys in Great Britain: the first was undertaken from 1985-88, then the second in 1994-97. Based on the results of these surveys, it was estimated that the number of badger social groups had risen by 24%, from 42,000 in the 1980s to 50,000 in the 1990s, and that the number of badgers had increased by 77%, from approximately 250,000 to 400,000. This increase was due mainly to increased family size, followed by colonisation of new unoccupied areas as the badger population recovered from past persecution (Wilson et al (1997) Changes in the British badger population).

The latest national sett survey was undertaken between November 2011 and March 2013. It estimated that there were 71,600 social groups across England and Wales, with 64,000 of these in England. This represents a 103% increase in the number of social groups in England since the 1980s (Judge et al (2013) Density and abundance of badger social groups in England and Wales 2011-2013).  The number of badgers per social group is highly variable, so it's not yet possible to estimate the total number of badgers in England.  Assessment of the variation in the number of badgers per social group is ongoing.

The population density of badgers is limited by the environment in which they live. The pastures, meadows, hedgerows and woodlands of England and Wales create rich habitat with abundant food and shelter. One of the strongholds for the species is the south west of England. Here badger populations may have reached the natural carrying capacity, but in other areas, badgers are at much lower densities.

Badgers in the UK do not have any natural predators, though elsewhere in Europe cubs may be taken by mammals such as bears and wolves. The main ‘predator’ for the badger in the UK is currently the car, with 50,000 badgers killed on our roads every year.

What is the impact of a badger cull on other wildlife species?

The final report of the Independent Scientific Group on Cattle TB (2007) states that:
‘In addition to its effects on badgers themselves, proactive culling in particular had impacts on other wildlife species. Numbers of foxes (Vulpes vulpes) increased in proactive areas, in comparison with survey-only areas and, perhaps as a result, numbers of hares (Lepus europaeus) declined (Trewby et al., in review). Before culling, hedgehogs (Erinaceus europaeus) were rare in parts of RBCT areas where badgers were abundant (Young et al., 2006), and badger culling increased their numbers (G. Wilson, personal communication).’

Will culling badgers help hedgehogs? 

While badgers do prey on hedgehogs, the significance of the impact of badger predation compared to the impact of the many other factors affecting hedgehogs is not clear and there is little evidence to suggest that badgers are the principle driver of UK hedgehog decline. Some of the areas that have experienced the most dramatic declines in hedgehog populations are those with the fewest badgers (e.g. East Anglia) and in some areas, where habitat is good and invertebrates are common, the two coexist without any decline in hedgehog numbers.

Hedgehogs and badgers have coexisted for thousands of years. They have very similar diets and therefore compete for resources. Competition becomes more intense when food becomes scarce, and any pressure on the food supply may cause a shift from competition to predation of hedgehogs by badgers. As with all predator-prey interactions, this is a natural and essential part of a functioning ecosystem.

The badger is considered a forager rather than a predator and in the UK its diet is dominated by invertebrates (mainly earthworms) and plant matter. However, badgers are opportunistic and will eat a very varied diet and make use of whatever is locally abundant, including slugs, snails, berries, acorns, grubs, fruit, nuts, bulbs, crops (particularly maize), small mammals, carrion and eggs.

A systematic review of 110 studies of badger diet found that bird remains occurred in badger faeces at a frequency of just 7.97% for UK studies (5.55% for all studies combined) (Hounsome, T. and Delahay, R. (2005), Birds in the diet of the Eurasian badger Meles meles: a review and meta-analysis.
Mammal Review, 35: 199–209) and a recent study of badgers in Poland found hedgehog remains in fewer than 1% of faecal samples (Mysłajek R.W., Nowak S., Rozen, A. & Jedrzejewska B (2013) Diet of the Eurasian badger in the Western Carpathians and its implications for species conservation in Poland. Animal Biology 63 (2013) 271–284). Badger predation is therefore very unlikely to have a significant impact on the population of any single prey species. 

Recent analysis (Trewby ID, Young R, McDonald RA, Wilson GJ, Davison J, Walker N, et al. (2014) Impacts of Removing Badgers on Localised Counts of Hedgehogs) of data from the Randomised Badger Culling Trial has formed the basis of an argument that badgers should be culled to conserve hedgehogs, since it was found that hedgehog numbers increased in some areas of grassland following badger culling. The Wildlife Trusts do not consider this sufficient evidence to advocate culling badgers as a means of increasing hedgehog numbers, particularly where a range of more suitable and effective management alternatives are available.

Who will pay for the culls and how much will they cost?

The Government's badger control policy is based on a cost-sharing approach with the farming industry. The industry is responsible for the operational costs of delivering culling and Defra bears the costs of licensing, monitoring and policing the policy. Defra estimated the cost of various options:

Licensing: £377,000 per cull area
Co-ordination: £20,000/area/year 
Culling using cage trapping: £2,500/km2/year, for 4 years
Culling using controlled shooting: £300/km2/year, for 4 years
Culling using a combination of methods: £1,000/km2/year, for 4 years
Vaccination: £2,250/km2/year, for 4 years
Monitoring: £737,000 per area
Policing: £500,000 per area/year, for 4 years

However, it has been estimated from Defra figures that the pilot culls in Somerset and Gloucestershire have so far cost the taxpayer more than £16 million - far exceeding anticipated figures.

What will happen after the pilot culls?

An independent panel of experts was tasked with assessing the safety, humaneness and effectiveness of the first year of the pilot culls and their final report deemed them 'ineffective' and 'inhumane'.  There was no independent monitoring of the second year of culling but the culls in Somerset and Gloucestershire will continue in 2015, and have been rolled out to Dorset.  The Government has indicated the intention to roll out culling to more areas in future years.

Are The Wildlife Trusts allowing culling on their land?

No.  None of the 47 Wildlife Trusts will allow badger culling to take place on their land.

What is the perturbation effect?

During the Randomised Badger Culling Trial (RBCT), culling consistently increased the prevalence of bTB in badgers.  Culling disrupts badger social structure, causing them to move around more frequently and over longer distances - this effect is known as perturbation, and the idea that it may result in increased disease transmission (to other badgers and to cattle) has been termed the 'perturbation effect.'

Badgers typically live in social groups of four to seven animals with defined territorial boundaries. In a stable badger population, there is limited movement from one area to another. As a result, a badger setts harbouring high levels of bTB infection would tend to remain relatively isolated. Removing badgers from cull areas opens up the territory, allowing badgers to come in from the surrounding areas. Badger movements around and beyond the infected area therefore increase, and immigrant badgers are at risk of infection from abandoned setts and unculled infected animals. Badger to badger transmission increases along with the likelihood of badger to cattle transmission. Because the population is still lower than the carrying capacity of the total area, badgers move around much more than they did before the cull, and this movement distributes the original infection over a wider area. This is known as the 'perturbation effect'.

Can a cull be designed to avoid the perturbation effect?

The Independent Scientific Group on Cattle TB concluded in its final report (2007) that it was “unable to conceive of a system of culling, other than the systematic elimination, or virtual elimination, of badgers over very extensive areas, that would avoid the serious adverse consequences of perturbation.”

Why do The Wildlife Trusts think six weeks too long for a cull?

The majority of culling operations during the RBCT occurred over a period of eight to eleven consecutive nights. On four occasions culling took place sector by sector over several months but this method was associated with a greater rise in TB prevalence in badgers.

In the Republic of Ireland is there a research study that proves that badger culling works?

A large scale trial of the effects of badger culling on cattle TB incidence has been undertaken in the Republic of Ireland known as the Four Areas Trial. The outcomes cannot be directly compared with the RBCT due to differences in methodology including use of snares and geographical boundaries such as coastline and rivers.

What about the 'test and vaccinate or remove' approach?

Research is underway in Northern Ireland to investigate the impact of a 'test and vaccinate or remove' approach, which involves the TB testing of live badgers; vaccinating and releasing the badgers that test negative (TB free); and humanely euthanising badgers that test positive (TB infected).  The programme began in 2014, when all badgers trapped within the trial area were sampled, microchipped and vaccinated against bTB.  From 2015 to 2018, badgers in the trial area will be trapped annually and all badgers that test positive for TB will be removed.  It is not yet known whether this approach could cause perturbation, and there are some concerns that the tests available to detect TB in live badgers are not sufficiently accurate (risking both false positives and false negatives).  The completion of this work and full analysis of the resulting data will provide useful evidence as to whether this is a viable approach. 

Could PCR testing be used to identify infected setts?

PCR testing (Polymerase chain reaction testing which tests for TB DNA) would allow the detection of M.bovis (the bacterium causing bTB infection) in the wider environment and provide a measure of environmental contamination, which can occur when infected animals - whether cattle, badgers or other vectors - shed bacilli in their urine or feces.  It has been shown that M. bovis can remain active in cattle slurry for over 6 months, persist in the soil for up to 15 months, and persist in water for up to 58 days.  Being able to quantify the location, extent and impact of environmental contamination would therefore help reduce the risk of disease transmission, since cattle could in theory be kept away from contaminated pasture and other areas. 

It has been proposed that PCR testing could be applied to badger latrines to detect fecal shedding within badger populations, and by inference locate and cull 'infected setts'.  Given that even small scale disturbance of badger populations can lead to perturbation and therefore increased disease risk to cattle, it is not yet clear whether targeted culling informed by PCR testing would be a viable option.  Culling of this nature would still risk removal of healthy badgers.

What about other countries? Haven’t they tackled the problem in the wildlife reservoir?

Quotes about potential TB control in other countries often overlook key facts. In New Zealand, possums are culled to deal with bovine TB but, unlike badgers, they are non-native mammals and are also culled for conservation reasons to protect native bird species. This is therefore not a justified comparison to the situation in England. Moreover, in Australia and New Zealand there are much more rigorous programmes of local cattle herd depopulation, movement restriction and reintroduction when there has been a breakdown. This has not been accepted as part of bTB control in England.

What is the policy of the Welsh Government?

The Welsh Government announced in March 2012 it would undertake a badger vaccination project within the TB Intensive Action Area (IAA) in west Wales as part of its bTB eradication programme. In 2014, a total of 1,316 badgers were vaccinated at a cost of £929,540 and more than 5,000 doses of vaccine have been administered in the last three years.  None of the badgers trapped showed visible signs of disease.

The Welsh bTB eradication policy focuses heavily on cattle measures.  According to Chief Veterinary Officer for Wales, Prof. Christianne Glossop, incidence of bTB in Wales have fallen by 28%; the number of infected cattle slaughtered has fallen by 45%; and 94% of Welsh herds are TB free.  This has all been achieved without culling badgers.

What are the potential benefits of cattle vaccination?

Cattle vaccination offers the best long-term way to reduce bTB in the cattle population. A sustained vaccination programme would be required with annual re-vaccination.

Is a cattle vaccine available?

The research and testing of a vaccine has been completed and also trialled in Ethiopia, but it is not yet technically called a vaccine in this country as it has to be accredited. However, accreditation for the European market cannot be progressed whilst an EU ban remains in place on the use of such a vaccine.

What changes are needed to allow a cattle vaccine?

Vaccination of cattle against bTB is currently prohibited by EU legislation, principally because BCG vaccination of cattle can interfere with the tuberculin skin test which is the recognised primary diagnostic test for TB in cattle. A test called a DIVA (see below) test could help resolve this issue.

What is a DIVA test?

The Animal Health and Veterinary Laboratories Agency is developing a test to differentiate infected from vaccinated animals - the Differentiating Infected and Vaccinated Animated (DIVA) skin test. This test would be used alongside the tuberculin skin test to confirm whether a skin test positive result is caused by vaccination or TB infection.

Why vaccinate badgers?

The aim of badger vaccination is to reduce transmission of bTB between badgers, and between badgers and cattle. BCG vaccination reduces the severity of the disease, the shedding of bacteria from infected individual badgers and therefore the disease’s prevalence in badger populations. 

In a clinical trial, BCG reduced the risk of vaccinated badgers testing positive to a test of progressed infection by 74%, and reduced the risk of testing positive to any of the available live tests of infection by 54%.  In the same clinical trial, BCG vaccination reduced the risk of infection of unvaccinated cubs in a vaccinated social group - when more than a third of the social group was vaccinated, the risk to unvaccinated cubs was reduced by 79%.  Vaccination is unlikely to have an effect (either positive or negative) on the course of existing infections in badgers, and the vaccination of previously infected badgers has not been seen to enhance the excretion of M.bovis (the bacterium causing bTB infection.)

Is there an oral badger vaccine?

An oral vaccine is in development.  Badgers are currently vaccinated by injection.

Is it true that there are no benefits before five years in a badger vaccination programme?

No. Research has shown that vaccination benefits individual badgers by reducing the progression, severity and excretion of bTB. Population-level benefits do take time to achieve, with longer vaccinating programmes being more beneficial than shorter ones.

Will badger vaccination reduce the incidence of bTB in cattle?

Badger vaccination can be expected to reduce the incidence of bTB in cattle in high-incidence areas but no trial has been conducted to assess the size and timing of these impacts.

How can improved biosecurity measures help?

Contact between cattle and badgers or their excretions may pose a risk of infection and improving biosecurity on farms can reduce this risk. The main transmission route between badgers and cattle has not yet been proven. Studies indicate direct contact between grazing cattle and badgers seems infrequent but transmission may occur via contaminated pasture or around farm buildings. Best practice videos and leaflets are available from the Defra website along with the following advice:

• Keep badgers away from stored cattle feed: badgers infected with TB can contaminate feed.
• Make your farmyard less attractive to badgers: badgers are likely to be attracted to accessible feed and may spread disease to cattle.
• Be aware of main badger latrines and active setts at pasture: where possible keep cattle away from these high-risk areas.
• Keep cattle away from neighbouring cattle herds: disease can spread between cattle.
• Protect your herd: source bought in stock carefully and adhere to isolation procedures for any inconclusive or reactor animals.

A research study by the Food and Environment Research Agency (Fera) concluded that simple exclusion measures are 100% effective in preventing badgers entering farm buildings when deployed properly. The badger exclusion measures were individually tailored to fit the requirements of each farm and sought to secure every potential entrance point on each selected facility.

If The Wildlife Trusts support the killing of species such as ruddy ducks and American mink, why do they oppose the cull of badgers?

Controlling some non-native species can be necessary sometimes where they are proven to threaten the conservation status of native wildlife. We only support the killing of wild animals when a strong scientific case has been made for the impacts and where it would be effective and humane. We oppose the large scale culling of native mammals.