Bovine TB: consultation on proposals to introduce licensed badger control to prevent the spread of bovine tuberculosis in the Low Risk Area (England) Response from the Zoological Society of London

Bovine TB: consultation on proposals to introduce licensed badger control to prevent the spread of bovine tuberculosis in the Low Risk Area (England)

Response from the Zoological Society of London

The Zoological Society of London (ZSL) has a long history of scientific engagement with the

management of bovine tuberculosis (TB) in British cattle and wildlife. We have commented on

each of the seven issues on which Defra has requested views. Our responses are based upon

scientific evidence, and supported by references to the literature wherever appropriate.

(a) The principle of controlling the risk from badgers with TB in the LRA

In the High Risk Area (HRA), badger populations are managed with the aim of reducing the

immediate risk of TB transmission from infected badgers to cattle. The consultation document

indicates a similar aim for the Low Risk Area (LRA). However, an additional or alternative aim

would be to reduce the risk of TB transmission from infected cattle to badgers. This latter aim

is especially appropriate for the LRA where, as the consultation document states, sporadic TB

incidents are caused mainly by movements of cattle from the HRA. In such circumstances,

minimising cattle-to-badger transmission could avoid badger populations becoming infected,

for example from bought-in cattle, reducing the longer-term risk of badger-to-cattle infection.

The risk of badger-to-cattle transmission is likely to be so low in the LRA that managing

badgers may not be worthwhile. In the HRA, the best estimates indicate that just 5.7% of TBaffected

cattle herds (95% confidence interval (CI) 0.9-25%) acquire infection from badgers1.

This figure is probably even lower in the LRA, where the consultation document indicates that

fewer badgers are likely to be infected, with most herd infections caused by bought-in cattle.

Hence, badger management to avoid badger-to-cattle transmission in the LRA may provide a

poor return on investment.

In contrast, managing badgers to avoid cattle-to-badger transmission in the LRA is much more

likely to be useful. There is strong circumstantial evidence that cattle transmit M. bovis to

badgers2, and hence a risk that moving infected cattle into the LRA might lead to localised

infection in the badger population, increasing the risk of longer-term transmission back to

cattle. Hence, badger management to avoid cattle-to-badger transmission in the LRA may

indeed be worthwhile.

It is important to distinguish whether the short-term aim of badger management is to reduce

badger-to-cattle transmission or cattle-to-badger transmission, because the two forms of

transmission are likely to require different forms of management. Badger culling is used in the

HRA with the aim of reducing badger-to-cattle transmission; however culling badgers is very

unlikely to reduce cattle-to-badger transmission. In contrast with culling, badger vaccination

should have the capacity to curb cattle-to-badger transmission3.

Badger vaccination differs profoundly from badger culling in that, while culling can increase

TB transmission as well as reducing it2,4-12 there is no evidence that badger vaccination causes

harmful effects in either badgers or cattle3,13-15. For this reason, vaccination can be

implemented in smaller areas than culling, and for shorter time periods, without fear of illeffects.

Furthermore, in comparison with culling, vaccination has fewer welfare implications,

is cheaper, and is more publicly acceptable. For these reasons, badger vaccination could in

principle be implemented routinely as soon as cattle infection is detected in the LRA, as a

precautionary measure, pending investigation to determine whether the badger population is

infected, and before taking a decision about whether vaccination would be repeated in

subsequent years.

On this basis, ZSL supports the principle of badger vaccination in the LRA, but not the

principal of badger culling.

(b) The principle of a government-led badger control operation where required.

Government-led badger management was discontinued in 2005 to reduce costs to taxpayers.

However, government-led operations are more easily coordinated and quality-controlled than

those led by farmers, and might be especially appropriate where a small team of specialist

staff is needed to implement multiple localised operations.

However, we are concerned by the suggestion in the consultation document that such

government-led action might be conducted outside the provision of the Protection of Badgers

Act. If culling in the LRA is unlikely to fulfil “the purposes of preventing the spread of disease”,

as required by the Protection of Badgers Act, then it should not be pursued. Moreover,

Parliament voted to protect badgers and, in seeking to bypass the Act, government risks

sending a message that it tolerates killing of protected species.

We also note that the consultation document cites – without attribution – the wording of the

Animal Health Act, referring to a hope that culling would “substantially reduce or even

eliminate” TB. The Animal Health Act allows ministers to take strong action (e.g. to authorise

“methods of destruction that would otherwise be unlawful”) if convinced that such action is

necessary to “eliminate or substantially reduce” disease risks. A plan to cull badgers in Wales

under the Animal Health Act was overturned by Judicial Review, and many of the legal

arguments against that proposed cull would apply even more strongly in this case, as there is

consistent scientific evidence that small-scale culling increases cattle TB4-9,12 rather than

“substantially reducing” it. Moreover, the availability of badger vaccination as a more

appropriate tool in the LRA indicates that such culling is certainly not “necessary”.

(c) The principle of taking a precautionary case-by-case approach, dependent on the local

conditions and situation, including as regards the number of years in which culling is

carried out.

ZSL challenges the notion that the proposed approach is precautionary. The precautionary

principle indicates that action should be taken to avoid causing harm, even if the probability

or magnitude of harm is uncertain. In contrast, small-scale badger culling is an action

associated with strong evidence of causing harm rather than preventing it. The precautionary

principle thus provides no justification for small-scale culling. In contrast, badger vaccination

might be used as part of a precautionary approach, as it does not cause harm.

Regardless of whether Defra’s planned approach is precautionary, we are concerned that it is

perilously vague. No criteria are provided to indicate the circumstances when culling would

be preferred over vaccination, how large an area should be targeted, how many times culling

or vaccination should be repeated, what proportion of land access would be required, and

what level of population reduction would be needed. Such criteria are important for two

reasons. First, it is well-established that badger culls which are small-scale, patchy, or shortterm

can increase cattle TB rather than reducing it16,17; hence clear criteria are needed to

avoid harmful impacts on cattle health. Second, badger culling requires killing a protected

species, an action that would be unlawful unless legally justified on disease control grounds.

Hence, clear criteria are needed to show that the proposed action would have disease control

benefits sufficient to justify destruction of protected wildlife. In the LRA, evidence suggests

that sustained large-scale badger culling would be unjustifiable on conservation and cost

grounds, and small-scale culling unjustifiable because it is ineffective. By contrast, badger

vaccination could be a promising way to reduce TB spread.

(d) The principle of using culling or vaccination or a combination of the two to control

risks from badgers with TB in the LRA

As noted above, ZSL supports the principal of using badger vaccination within the LRA.

ZSL does not support the principal of using badger culling in the LRA. As noted above, badgerto-

cattle transmission of M. bovis is likely to be very infrequent in the LRA, and attempting to

prevent it by culling unlikely to be worthwhile. Minimising cattle-to-badger transmission in

the LRA might be worthwhile, but is unlikely to be achievable by culling. In the LRA, evidence

suggests that sustained large-scale badger culling would be unjustifiable on conservation and

cost grounds, and small-scale culling unjustifiable because it is ineffective4-9,12.

The consultation document states that “The aim of introducing badger control in the LRA would

be to … prevent further geographic spread of TB in badgers”. In contrast with this stated aim,

there is strong evidence that badger culling causes the “geographic spread of TB in badgers” as

well as in cattle, by disrupting badger movement patterns and hence increasing contact with

other badgers and with cattle5-7,9,10,18,19. Indeed, the Godfray et al. paper16 cited in the

consultation document states that “small-scale… badger culling… may exacerbate the disease

problem through a perturbation effect”.

The consultation document dismisses the risk of perturbation, stating that “the risk of the

perturbation effect is… much lower than that in the HRA and Edge Area” because “the

perturbation effect is associated with infected badgers outside of the cull area increasing their

roaming” and “there is no evidence which points to widespread infection in the badger

population across the LRA”. These statements indicate a misunderstanding of how

perturbation occurs within badger populations*. Perturbation is not thought to result from

infected badgers entering a culled area; rather, culling increases mixing within the badger

population, encouraging transmission among badgers remaining in the culling area, and

between such badgers and those immigrating from adjoining land2. Such mixing need not

involve immigration of infected individuals; it is possible that immigration could provide a

supply of susceptible (uninfected) individuals which become infected through contact with

individuals which survived the cull. Importantly, such altered badger behaviour has been

linked to increased cattle TB, indicating that the harmful consequences of badger behaviour

change can exceed the beneficial consequences of lower badger numbers.

*Defra’s claim that perturbation is unlikely to occur in the LRA contrasts with its parallel claim that “rapid geographical

spread is likely to be more of a risk” in the LRA because such spread “is likely to occur when social groups are disrupted or at

lower densities” and “much of the LRA has a lower density of badgers”. Defra’s expectation of rapid TB spread through the LRA

badger population confuses naturally low population density with population density which has been artificially reduced by

culling, two different phenomena likely to have different consequences for badger movement and hence TB spread. In the

absence of culling, badger density is determined by food availability20. When food is abundant, many badgers are born but

few die, and the population grows. When the number of badgers matches the food supply (termed carrying capacity), many

badgers have enough food to survive but not to breed21,22; the birth rate slows21,22, and the population stabilises. At carrying

capacity, immigration is rare because the badgers born into a territory fiercely defend its resources from intruders23. But,

when culling suddenly reduces badger numbers, there is more food, and fewer badgers to defend it. Some of the badgers that

were unable to breed in their home territories move to exploit food and breeding opportunities in the culled area, and this is

what causes perturbation2,24. But those badgers only move because the culled area is below carrying capacity, that is, it

contains fewer badgers than the environment could support. In contrast, if carrying capacity is naturally low, badger density

is low but immigration would still be rare, because immigrants would not be able to exploit untapped food resources by

moving. Evidence suggests that badger social organisation across the low TB risk areas of northern England (density

4.9/km2)25 and Scotland (densities 1.9-6.0/km2)20 is similar to that observed in high risk areas of Cornwall (4.2-6.5/km2)26,27,

Avon (5.8/km2)27, Staffordshire (6.2/km2)28 and Gloucestershire (25.3/km2)29, with consistently stable territories and low

home range overlap. There is thus no strong justification for expecting more rapid TB transmission between social groups in

the LRA, and likewise no reason to dismiss the risk of perturbation.

ZSL is likewise opposed to combinations of culling and vaccination. Our own research

suggests that concurrent vaccination and culling, as conducted in Test-Vaccinate-Remove

(TVR) programmes, risks increasing cattle TB rather than reducing it11. Vaccination after

culling – sometimes portrayed as an exit strategy from culling – is unpromising because, while

vaccination impedes disease transmission by protecting susceptible animals30, culling

increases prevalence2 and is thus expected to reduce the effectiveness of vaccination. In

general, vaccination and culling work by different mechanisms and are unlikely to be more

effective when used in combination. ZSL considers vaccination on its own to be a more

promising approach.

(e): In relation to cases where culling is deployed, the principle of lowering the badger

population of the affected area sufficiently to reduce the risk of infection of cattle from

badgers (whether through direct or indirect contact), and ideally substantially reduce or

even eliminate it.

It is very unlikely that reducing the local badger population through small-scale culling will

“substantially reduce or even eliminate” the risk of M. bovis transmission to cattle in the LRA.

Multiple studies have shown that small-scale badger culling increases cattle TB2,4-12, but there

are no studies which have detected benefits of localised culling†.

We are concerned that the wording “substantially reduce or even eliminate” reflects the text of

the Animal Health Act, which allows ministers to take strong action (e.g. to authorise “methods

of destruction that would otherwise be unlawful”) if convinced that such action is necessary to

“eliminate or substantially reduce” disease risks. As noted above, evidence indicates that

localised badger culling will not “eliminate or substantially reduce” TB risks to cattle, and the

availability of badger vaccination as a more appropriate tool in the LRA indicates that such

culling is certainly not “necessary”.

(f): On the proposed revisions to the Guidance to Natural England on licensed badger

control. Draft revised Guidance can be found at Annex B. See the new section on Low Risk

Area Badger Disease Control. The new section header and other revisions to the Guidance

have been highlighted in yellow for ease of reference.

As we have indicated above, we are concerned that the Guidance to Natural England provides

no criteria to determine the geographical extent, timescale, landowner consent, or population

reduction needed to deliver a cull likely to “prevent the spread of disease” and therefore justify

licensing under the Protection of Badgers Act. Indeed, as there is no evidence to show that

small-scale badger culling can “prevent the spread of disease”, but strong evidence that such

culling can increase disease spread2,4-12, the draft Guidance requires Natural England to ignore

scientific evidence in issuing licences to kill a species it is charged with protecting.

On a much smaller point, we wonder why the section entitled “The Policy” makes no reference

†We also note that the wording of this question suggests confusion about the role of contact between badgers and cattle.

“Direct contact” refers to very close physical proximity between badgers and cattle, allowing transfer of bacteria from one

host species to the other31; this contrasts with “indirect contact”, which entails one host species shedding bacteria into the

environment, where the other species encounters it and becomes infected. Direct contact is very uncommon31-33, and indirect

contact is thought to be a more important transmission route. Reducing badger density may not reduce indirect contact risk,

because badgers change their defecation and urination behaviour when their territorial system is disrupted34. However, the

distinction between these forms of transmission is not highly relevant to this consultation question. We wonder whether

Defra is referring instead to the fact that cattle herds originally infected by badgers (badger-to-cattle transmission) may go on

to infect additional herds (cattle-to-cattle transmission), with the latter causing a higher proportion of TB cases than the

former1. Management which prevents badger-to-cattle transmission may thus prevent onward cattle-to-cattle transmission,

magnifying the apparent benefit of such management. However, management targeted directly at cattle-to-cattle

transmission (such as improved testing and controls on cattle movement) is still more promising, and carries no risk of

increasing cattle TB.

to licences for badger vaccination, although the consultation document indicates that

vaccination would be part of the policy.

(g): Any additional comments or approaches which you feel are relevant but not captured by

the questions above.

We have two additional comments.

First, we note that Defra proposes to allow both culling and vaccination only “when all other

cattle and biosecurity measures have been put in place… and there is epidemiological evidence that

the disease is present in badgers”. We recognise the reason for this restriction on the

implementation of culling; however we suggest that no such restriction is necessary in relation to

vaccination. To the contrary, we suggest that vaccination could be most usefully deployed

immediately on detection of cattle TB, without waiting for evidence of infection in the badger

population. Such vaccination would be expected to reduce the risks of cattle-to-badger

transmission during breakdown management. Samples could be collected in the course of

vaccination, and vaccination then repeated in subsequent years only if infection were detected, or

breakdown management prolonged.

Second, and more generally, we are concerned that the document fails to convey uncertainty

concerning the outcome of badger culling. For example, the statement that “This action will

avoid future breakdowns and reactors in the affected hotspot area and so deliver an economic

benefit to both industry and government” ignores all the evidence that small-scale culling has

been consistently linked to increased cattle TB (and never shown to deliver reductions in

cattle TB). Likewise, the entire section on the “Benefits” of the proposed approach is based on

an unfounded assumption that small-scale badger culling will reduce cattle TB. Such failure to

portray evidence and uncertainty leads to a consultation document which risks misleading

the public being consulted, undermining the principal of public consultation.

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