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BADGERS AND BOVINE TUBERCULOSIS

Content Updated: 4th October 2013

UPDATE (October 2013): The data surrounding bovine tuberculosis, paticularly in regard to the affected wildlife reserviors is constantly changing. Consequently, it is unlikely you will find a single resource that is constantly up to date. With that in mind, the reader is directed to the DEFRA's Bovine TB website, which contains the most up to date statistics on the disease. Badger biologist Martin Hancox presented the anti-cull debate on his Great Badger and Bovine TB Debate website and -- although this no longer appears to be online -- the crux of his argument is available as a PDF (click here to open it in a new window), while the National Farmer's Union also has a channel discussing bovine TB that's worth a read. Please be aware that there are very few impartial websites on this topic and, as always, I would advise the reader looks at as much of the evidence as possible before making up their own mind. N.B. Many of the links to other sites of interest at the bottom of this article were broken when DEFRA had a tidy-up of their website; these have now been fixed.

European badgerThe first record of tuberculosis in Meles meles came from Switzerland during the mid-1950s. In 1971, a dead badger recovered from the Cotswold Hills in Gloucestershire (UK) was found to be infected with Mycobacterium bovis, the bacteria known to cause tuberculosis in cattle (that is to say, bovine tuberculosis, or bTB for short). This specimen represents the first case of a badger infected with bTB from Britain.

In humans, TB is typically caused by M. tuberculosis. However, M. bovis is a close relative of M. tuberculosis and can be equally problematic for humans. During the 1930s, the incidence of M. bovis in children (and cats) was high; the bacterium was contracted through the consumption of unpasteurised milk. The implementation of milk sterilization and pasteurising lead to a dramatic decline in human bTB cases, although people in prolonged contact with cattle or their meat (i.e. slaughter houses) have been known to contract M. bovis infections – according to the Institute of Animal Health in Berkshire (UK), around 2000 people currently die of bTB each year, globally. Today, TB as a complex is the world’s biggest bacterial killer, estimated to kill three million people annually.

At the bottom of this summary, I have provided several links to the Department for Environment, Food and Rural Affairs (DEFRA, which superseded the Ministry for Agriculture, Fisheries and Food, or MAFF, in 2001) reports, which will give you a much more comprehensive view of the problem than I intend to provide here. Anyhow, for the uninitiated, here are the basics.

CowQ: What is Bovine TB (bTB) and why is it a problem?

A: Tuberculosis is an infection of the respiratory system caused by bacteria of the genus Mycobacterium; in humans Mycobacterium tuberculosis is typically the causative agent, while it is M. bovis that causes the disease in cattle. M. bovis can also be passed to other mammals, including badgers, deer, foxes, domestic cats and dogs and even humans; humans are, however, considered to be at very low risk from this particular strain, with fewer than 0.5% of the human TB cases between 2000 and 2009 caused by this species of bacteria.

When the bacteria enter the lungs they reproduce and cause severe pulmonary distress, creating lesions in the lung tissue; they may subsequently spread to the lymph nodes and to other organs in the body. The disease can cause the animal to be lethargic, lose its appetite and cough, but the typically slow progression of the disease means that such symptoms are rarely seen.

Currently, the UK experiences some 4,500 herd incidents per year, resulting in the compulsory slaughter of about 35,000 cattle, which is 0.7% of the 5.3 million cattle DEFRA estimated present in England at the end of 2012. This 0.7% may sound trivial but, because of the clustered nature of outbreaks, the local percentages can be much higher – in Cornwall, for example, only 46 (4.6%) of the 1,000 dairy herds with 50-or-more cows, have never been restricted for TB between 1990 and 2012. Such herd breakdowns, cattle dispatching, compensation to farmers, surveillance, etc. is estimated to cost the UK almost £90 million per year. In a recent report, published in June of this year, the House of Commons Environment, Food and Rural Affairs Committee estimate that bTB has cost the UK taxpayer more than £500 million in the last decade and predict that it will cost more than £1 billion over the next 10 years.

Instances of TB infection in cattle rose from the mid-1980s, with significant peaks during 2001, 2005 and 2008, associated with the Foot and Mouth outbreak and changes to way parishes were tested. bTB cases (i.e. number of cattle slaughtered) fell in 2009 (3% drop on 2008, or 1,030 fewer cases), dropped by 16% in 2010 (i.e. 6,034 fewer cases than in 2009), rose by 7% in 2011 (i.e. 2,299 more cases than in 2010) and rose by a further 10% in 2012 (i.e. 3,504 more cases than in 2011). Currently large areas of south-west England, central western England and Wales are now badly affected.

 

Q: Are badgers the only transmitter of bTB?

A: Fallow deer (Dama dama)No. To further complicate the issue, although badgers seem to have a considerable tolerance to the infection, they are not the only species capable of transmitting the bacterium. However, while badgers may not be the sole route of wild-domestic transmission, they are one of the few species that can act as effective vectors, because the disease is rarely fatal to them. Despite the observation that, even in the most susceptible species, bTB infection can persist for many months (even years) before it becomes fatal, not all species that can become infected with the bacterium are effective carriers (most die fairly soon after contracting the bacilli). Badgers seem to have a remarkable tolerance to the bacterium and generally between 50% and 80% of tuberculous individuals have no observable lesions. Moreover, a paper published in The Veterinary Record during 1998 reports that infected badgers generally have few sites of infection and small numbers of the bacilli in their tissues. In the UK, badgers are the only known maintenance host for M. bovis, although there are some “spill-over hosts” (i.e. populations in which infection will persist where a maintenance host is present in the ecosystem), including ferrets and Red foxes.

A review of M. bovis infection in wild mammals from the UK, headed by Central Science Laboratory (CSL) biologist Richard Delahay, lists ten species (excluding the badger) from which this bacterium has been isolated. Included in this list are Fallow deer (Dama dama - right), Red fox (Vulpes vulpes), Mink (Mustela vision), Mole (Talpa europaea), Brown rat (Rattus norvegicus), Ferret (Mustela furo) and Domestic cats (Felis domesticus). A recent study of 1,307 Bank voles (Myodes glareolus) found that only one yielded positive results for M. bovis, leading the authors to suggest that this species is relatively unimportant as a reservoir for bTB. Similar studies have shown that rabbits and mice can be experimentally infected with bTB, although no records are known from the wild.

Some evidence suggests that sex and age may affect susceptibility to M. bovis, while the stage of disease progression seems to influence mortality. In a paper to the Journal of Zoology in 2000, a group of scientists fronted by David Wilkinson (CSL) report that, while ELISA-Positive badgers (i.e. incubating bTB, but not excreting the bacilli) at Woodchester Park did not have a substantially higher death-rate than uninfected individuals, infected badgers that were excreting M. bovis did. The study also found that the progression of the disease is considerably more rapid in males than it was in females; females ultimately seemed to cope with the disease better than the males. Similarly, the susceptibility of badgers to M. bovis infection may be related to age, although studies to date have yielded mixed results. One 1991 paper found that infection rate was slightly higher in cubs than in adults (46% and 39%, respectively), while another paper from 1998 found the opposite (13% of cubs and 20% of adults).

There are also data from Ireland to suggest a connection between irregular bacula development (potentially affecting reproduction?) and incidences of bTB infection.

Q: How do we test cattle for TB and what is a ‘herd breakdown’?

A: Cattle are subjected to the Comparative Intradermal Tuberculin Test (CITT, more commonly referred to as simply a skin tuberculin test), which involves injecting protein extracts (tuberculins) from the Mycobacterium bacteria into the cow. The first injection contains M. bovis tuberculin and is made into the cow’s neck. A second injection, this one containing M. avium (a bacteria causing TB in birds) tuberculin, is subsequently made about 13cm (5 in.) above the first, or on the other side of the neck if the animal is small. The immune system of most cows infected with bTB will react to the tuberculin, causing a local allergic reaction (swelling) at the injection sites; this change in skin thickness in response to the injections is measured 72 hours later. Comparing the size of the M. bovis tuberculin reaction to that of the M. avium allows the vet to separate cows infected with bTB from those infected with other strains. A cow is classified as positive (a “reactor”) if the bovis reaction is more than 4mm larger than the avium reaction, negative if there is no reaction, or inconclusive if the difference between the bovis and avian reaction is 4mm or less; reactors are isolated, valued (in order to pay compensation) and sent for compulsory slaughter, while inconclusive animals are usually re-tested after 60 days. If a reactor is found within a herd, movement restrictions are placed on the farm and it loses its “TB-free status”, which means no cattle can be brought on to or taken off the farm until it has been declared TB-free. The reactor cull and movement restrictions are referred to as a “herd breakdown”.

Critics of the CIIT test point out that it is only 65% to 80% effective; in other words, some 20% to 35% of cows may have bTB but test negative using this method. Factors such as pregnancy (during which the cow’s immune system is suppressed), certain parasitic infections and even the production of the test (tuberculin manufacture has been described as much an art as a science!) can all affect the CIIT’s effectiveness. In some cases, an additional test -- a Gamma Interferon blood test -- is also employed, which is more sensitive and quicker at detecting TB; this does, however, need to be conducted in a laboratory as it involves incubating a blood sample with tuberculin cultures.

Q: If farmers are compensated for their lost livestock, why is it such a big deal?

A: Because most farmers aren’t the heartless monsters that they are often portrayed to be. Having spoken to several farmers on this subject they have impressed two points on me: that the financial compensation is based on the most recent table of market valuations made by DEFRA, and may not represent what they would actually get for the cow at market; and the considerable emotional cost associated with losing the livestock, which can be devastating, particularly during serious or repeated outbreaks. Furthermore, the imposition of movement restrictions means that the farmer cannot sell any cows, nor add to his stock, which can impose further financial costs and add to the stress. From a broader view; the compensation, along with the cost of testing and cattle destruction, is a considerable financial burden on the UK tax payer.

Badger latrineQ: Where do badgers fit in?

A: Badgers, like all mammals, are susceptible to infection by M. bovis. Unlike most mammals, however, the disease tends to progress very slowly in badgers, such that they may live with infection for many years without any obvious clinical signs. The concern is that, during this time, they can spread the infection to other badgers and to any cows with which they share their territory. Indeed, the discovery of bTB in closed herds (i.e. those where cattle were not brought on to, or taken off of, the site) led to badgers being identified as a source of bTB in cattle. Some researchers dispute this view, however, suggesting instead that such outbreaks are actually a result of the 20%-or-so of the infected cattle that are not identified by the tuberculin test (something Martin Hancox refers to as a “huge hidden reservoir” of infection).

Originally, it was considered that infected cattle excreted the bacteria in urine, faeces and mucus on to feed and pasture, from where it was picked up by badgers. Infected badgers would subsequently excrete the bacteria in a similar manner (badger latrine - left) to the cows and this would allow the disease to spread to other herds in the area, or to other badger setts and thus herds further afield. Moreover, when reactors were identified and removed from the herd, infection could re-enter because the bacteria was still present in the local badgers and could be passed back to the herd. This way, you are confronted by two reservoirs: one in the cattle and one in the badgers, both of which needed dealing with.

We now know that the situation is far from straightforward, and research on a naturally infected population of badgers at Woodchester Park in Gloucestershire has shown that different individual badgers can have different ‘states’ of infection, affecting whether or not they’re a potential transmitter of the bacteria. Sex and age can also play a role in transmission. Research by biologists at the Central Science Laboratory in York, has shown that female badgers seem to cope better with bTB infection than males. The same dataset has also identified badgers within the population that were infected with, but were not excreting, M. bovis, living alongside those that were infected with and excreting the bacteria. In other words, infected badgers were not necessarily infectious badgers. The researchers found that ‘excretory’ badgers had a significantly higher mortality than ‘non-excretory’ or uninfected individuals, both of which had roughly the same mortality. So, badgers that were excreting M. bovis bacteria were likely to die younger than those that either didn’t have bTB, or were infected but weren’t excreting the bacteria.

We know badgers can contract the disease and in some cases they can be infectious (i.e. can give the disease to others) but, even some four decades since TB was first identified in a wild badger, we still know very little about how TB is spread between badgers and cattle, let alone how often such transmission occurs. Some researchers consider, based on the pathology of bTB, that cattle-to-cattle transmission is unimportant relative to badger-to-cattle transmission, while others maintain that bTB is a disease of cattle (not of badgers) and is not self-sustaining; in other words, bTB doesn’t persist in the badger population without infected cows present to continually ‘top it up’. Indeed, Professor Glyn Hewinson -- the Chief Scientist at the Animal Health and Veterinary Laboratories Agency -- summed the situation up quite nicely when he told the House of Commons Environment, Food and Rural Affairs Committee recently:

One of the real evidence gaps is how much TB is given from cattle to badgers, how much TB is given from badgers to badgers, how much TB is given from badgers to cattle and how much TB is given from cattle to cattle.”

This lack of data on transmission is actually more serious than it may sound, because it makes it exceptionally difficult to model and predict how any given strategy (i.e. culling, vaccinating, etc.) will work. Nonetheless, many people are of the opinion that we will never eradicate TB in cattle unless we first eradicate it from the wildlife reservoir.

Q: Why don’t we just vaccinate cows against TB?

A: This is probably the most common question I have come across in the last couple of weeks and it’s a good one. After all, vaccination is the standard method by which we go about protecting people and animals from infectious diseases. The problem, in this case, is that famers are not legally allowed to vaccinate their cattle, because the vaccine makes it hard to tell whether the cow is genuinely infected with bTB.

The European Union allows free movement of milk and dairy products within its member states provided certain hygiene standards are met. As we’ve covered above, cattle are tested for bTB using the tuberculin skin test, but vaccination with the only available vaccine (the Bacille Calmette-Guerin, or BCG) interferes with the skin test, making it difficult to tell infected cows from vaccinated ones. There is a test, referred to as the DIVA test, that can tell the difference between infected and vaccinated cattle, but it is expensive and not widely available. Either way, there is no provision in EU Directive 78/52/EEC for certifying products as being from ‘TB-free but vaccinated herds’. In essence, vaccinating the cows means that the UK would lose its ability to trade cow products with other EU countries; in 2011, trade in live cattle, meat and dairy products amounted to some £1.7 billion. The UK government would require a dispensation from the EC in order to initiate vaccine trials and, if such trials were successful, member states would have to vote to repeal the directive.

There are currently no field data from the UK, for the reasons discussed, to show how effective BCG vaccination of cattle would be in eradicating the disease, but small-scale studies from Ethiopia and Mexico suggest vaccination is up to 68% effective. Any vaccination would, however, provide a spectrum of protection, with some cattle being fully protected, some experiencing reduced disease, and some that derive no protection at all.

Q: Can’t we vaccinate badgers, instead?

European badgerA: An injectable BCG for use on badgers (appropriately named BadgerBCG) was licensed in March 2010 and has been used by several animal welfare charities as part of various badger vaccination trials in England and Wales. There are, as far as I know, no data from the field yet to show what, if any, impact vaccinating wild badgers has on bTB incidences, and five of six planned vaccination trials were cancelled by the coalition government. Studies on captive badgers have resulted in a lot of very misleading headlines and suggestions that vaccination is somehow a ‘magic bullet’ to the problem. One recent study, for example, was widely reported in the media as showing that the BadgerBCG reduced the incidence of bTB in badgers by 74%. In fact, the study found that, using one particular serological test, 4.5% of vaccinated badgers responded to challenge with the bacteria, compared with 17% of non-vaccinated animals. This is not the same as saying the vaccine protects 74% of badgers; it simply shows that, among this group of 262 badgers, there was a 74% reduction in one serological response to bTB challenge. Overall, the study suggests that there is a benefit to the vaccine, but it could not say how big the benefit was.

Generally speaking, vaccination studies on captive badgers show a moderate level of protection, with vaccinated individuals typically experiencing a slower progression of the disease, fewer bacteria in the lungs, fewer tissue lesions and, consequently, reduced shedding of bacteria. In none of the trials has vaccination cured the badgers of TB, but this is not to be expected (this is not how vaccines work). Indeed, many people have pointed out that vaccination will do nothing to help already infected badgers, which is true. The point with vaccination, however, is that it doesn’t have to be 100% effective and you don’t need to vaccinate 100% of animals. Instead the vaccine needs to be sufficiently protective, and sufficiently widespread in the population, to slow the progression of the virus such that it dies out; this concept is known as herd immunity. One study on captive badger cubs found that the chances of an unvaccinated cub testing positive for TB was only 21% when at least one-third of the social group had been vaccinated.

Owing to the lack of a cure for the disease, there has been a large movement supporting a cull of badgers to remove the “high proportion of sick badgers in TB hotspots” that would continue to spread the disease, followed by a proactive vaccination campaign to slow any resurgence of the disease. The problem, of course, is that trapping, testing and then shooting infected badgers is very labour intensive and expensive, so strategies more typically simply reduce the badger population in the area, culling healthy and infectious individuals alike. There are tests available that can detect TB infection from badger scats and could potentially be used to analyse latrines to identify infected clans for removal. Within the hotspot areas infection rates are generally considered to be around 20% (i.e. 1 in 5 badgers are infected with bTB).

Q: Where and why are DEFRA culling badgers at the moment?

A: In September 2012 Natural England issued a 21-condition licence, under the Protection of Badgers Act (1992), for a trial cull of badgers in western Gloucestershire (which began last month); the following month they issued a second licence, for a trial cull of badgers in western Somerset (which began earlier this month). The plan is for badgers to be ‘free shot’ (i.e. free-ranging badgers attracted to bait stations), or cage-trapped and shot, at night by trained marksmen using high-powered silenced rifles over a six-week period. The licences permit culling of badgers during the open season each year for four years. The plan is to reduce the badger population in each of the cull zones by 70%; based on earlier sett surveys conducted by DEFRA, this will equate to around 5,000 badgers. Animal welfare groups have raised concerns about the possibility that attempts to shoot low slung, muscular animals in the dark will lead to many badgers being wounded rather than killed outright.

Contrary to popular misconception, the trial culls taking place this year are not aimed at assessing whether culling badgers reduces incidence of TB in cattle. (As far as DEFRA are concerned, it does and this isn’t a matter of debate.) Instead, the culls are designed to assess how suitable such ‘free shooting’ is -- in terms of its practicality, safety and humaneness -- as a method of culling wild rural badgers at night. Some have questioned why only around 190 of the 5,000-or-so badgers that are due to be shot are being assessed for humaneness of the kill. A bigger problem for many, myself included, is that none of the carcasses are due to be tested for bTB, so a vast potential dataset of infection is being lost and we will have no idea how widespread TB infection is among these ‘hotspot’ badgers, nor how strains of TB are distributed among the badger population. DEFRA have said they see no need to test the badgers because tests are unreliable and they already have data on infection rates, while sceptics suggest that DEFRA don’t want to test the badgers only to find that the vast majority were free of the disease.

The UK signed up to the Bern Convention, a legally binding international agreement by which member states agree to conserve and protect their wild flora and fauna in their natural environments, in 1982. A complaint was submitted suggesting that the UK government were in breach of the conditions of the Bern Convention by giving the ‘green light’ to a cull. In September last year, however, the Bern Bureau Standing Committee met and decided that the proposed cull “should not cause a threat to the [badger] population if the monitoring is carried out properly.”

Cow with calfQ: Culling badgers in Ireland has reduced their incidences of TB in cattle, right?

A: It has certainly played a part in the Republic of Ireland’s TB control strategy. That said, it has also been argued that the frequent rigorous testing and slaughter of infected cattle, combined with better biosecurity has slashed the TB infection rates, and that the badger culling was actually irrelevant to the situation. If badger culling was pivotal to the reduction, the distribution and social structure of badgers in the RoI (which is different from that in south-west England), combined with the greater public acceptance of culling (even from animal welfare groups) may account for Ireland’s greater success rate. The situation is not straightforward, however, and the number of RoI reactors increased 13% between 2006 and 2007, despite continued culling of badgers. Interestingly, one Irish study found that when badgers were completely removed from the area and prevented from returning, there were no new cases of bTB in cattle for the 10 year duration of the study (1982-1992). The RoI are also further advanced in their research into badger vaccination than the UK, although there has recently been talk about the prospect of local badger extinctions, as well as a cull of deer (which are also a carrier of the disease).

Q: What’s the big deal with culling badgers?

A: All the evidence from culling trials suggests that localised culling of badgers can only achieve modest (i.e. 16-20%) declines in cattle TB rates when 70% or more of the population is removed. This culling strategy is extremely expensive, labour intensive and, perhaps more importantly, grossly unpopular with the general public, particularly animal welfare groups, which means culling operations are often subjected to protests and sabotage. Furthermore, because there is no consistent relationship between culling badgers and TB rates (i.e. a consistent cull, year-on-year, doesn’t result in a consistent decline in reactors), some argue that any reactor declines that happen when badgers are culled is actually no more than a coincidence, and it’s the weeding out of previously undetected infected cattle that causes the decline. Furthermore, the Krebs Trial found that, while culling badgers reduced TB incidences within the cull zone, it also increased incidences in neighbouring areas. This scenario was dubbed the “perturbation effect” and was believed to have been caused by infectious badgers, disturbed by the culling operation, moving out of the area and infecting nearby farms/badgers outside the cull zone. Again, not everyone subscribes to the perturbation hypothesis, pointing out that generally the problem is actually with badgers migrating into the cull zone to fill the vacuum left by the culling.

In the end, the big issue is that you have to kill a lot of badgers, many of which are not infected with the disease, for only modest declines in reactor rates. When you start culling it tends to be fairly straightforward, but as the programme progresses you’re left with progressively fewer and fewer badgers, now much more wary than at the start of the operation, and this increases both the difficulty and expense of the cull. Furthermore, culling can never offer a long-term solution because it must be regular (if not continual), in order to account for populations recovering and badgers immigrating into the area.

Q: Hasn’t the badger population exploded in the last decade? Surely, without any predators, their numbers need controlling?

A: There have been many statements circulated of late that cite how badger numbers have risen dramatically, thanks to legal protection granted in the early 1990s, to the point where the population is now ‘out of control’. The issue really is that we simply don’t know how many badgers there are in the UK and, more importantly, getting a handle on numbers is not a simple task because densities vary considerably with location and habitat type. The most recent data of which I am aware was an assessment of badgers published by the Joint Nature Conservation Committee during 2005, which estimated there to be 288,000 badgers in the UK. We don’t know how much, if at all, the population has changed since then, although in 2011 DEFRA initiated an £890,000 survey of badger sets in England and Wales -- to be conducted by the Food and Environmental Research Agency (FERA) -- in a bid to get an idea of the current badger population. FERA is due to publish their data in late 2013 or early 2014. The IUCN note that, by the end of the 1990s the badger population had increased by some 77% from mid-1980s level, although this figure has been questioned by some owing to the difficulties associated with determining the number of badgers in a social group. I have seen some extrapolations of these data that arrive at a population estimate of 800,000 animals, but these are essentially pure guesswork!

The question of whether the badger population has grown too large is a matter of opinion; badgers have long been considered a pest by some farmers, particularly where they have built large setts and caused damage to cereal crops. I have seen many calls for legal protection to be revoked, allowing farmers to control badgers on their land. I have not seen any recent estimates, but a survey in 1997 put the cost of damage caused by badgers (including damage to roads, crops, agricultural land, etc.) at just shy of £26 million per year. I have not seen any estimates of how much badger watching tours contribute to the British economy.

As I have discussed many times on this site, a population will not continue to rise indefinitely – it will rise until a limiting factor (e.g. space, food, water, shelter, etc.) imposes a constraint, at which point it will either remain stable or go into decline. The question, however, is how many is too many badgers? It’s very difficult to calibrate nuisance and one badger may be one too many if it’s causing you problems. In the end, we have a duty of care to our wildlife and balances must be struck at the local scale.

Q: So what is the solution?

badgerA: The short answer is that we simply don’t know! Logically, we need a proven cattle and badger vaccine that is cost efficient to administer. We need to repeal the EC directive that prevents UK farmers from vaccinating their cattle against bTB. We need more data on how TB spreads between badgers and cattle and how often it occurs. We need more sensitive TB tests that can not only detect a greater proportion of infected cattle and badgers (finding them all would be the ideal situation), but can also tell the difference between the response generated by natural infection and vaccination. Finally, we need a badger vaccine that can be delivered in bait in order to reach a larger proportion of the badger population more quickly and cost effectively than the current trapping and injecting strategy. In the short term, at least, the strategy may also require the identification and removal of setts proven to be infected with M. bovis. In reality, however, all of this costs money; money that the government almost certainly doesn’t have. With that in mind, it would seem that more effort needs directing at regular intensive testing and removal of infected cattle, tight biosecurity governing cattle movements, and more research towards how badgers and cattle can be kept apart in barns and the farmyard.

In the end, culling badgers is not going to solve the bTB problem in cattle – it may have an impact (although we simply can’t quantify this at the moment), but it will only be the control of TB in cattle through better detection, faster reactor removal and much tighter biosecurity on farms will solve the problem. Indeed, improved biosecurity measures imposed since the start of the year seem to be having a positive influence in reducing TB cases.

 

External Links

DEFRA Animal Health
DEFRA Tuberculosis in cattle
Gamma Interferon Blood Test
Impact of localized badger culling on tuberculosis incidence in British cattle (Nature abstract)
International Study Group Final Report on Bovine TB (PDF Document)
National Farmer’s Union Bovine Tuberculosis Positive and negative effects of widespread badger culling on tuberculosis in cattle (Nature abstract)
Tuberculin Skin Test
Tuberculosis Vaccine Trial (BBC News)
Update on Measures to Tackle Bovine TB (DEFRA)

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