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Image: Eurasian badger (Meles meles).
Home » Eurasian badger (Meles meles) » Articles :
Article 3: Do badgers infect cattle with TB?
Why some blame badgers for infecting cattle with bovine TB, and why others believe they are innocent.
See also: 1: Culling in Britain and 2: Background on Bovine TB
On this page:
Introduction | Arguments for | Arguments against | Related Badger Pages
Note: Since this page was first prepared, more conclusive information has become available showing that the major source of TB infection in cattle is in fact other cattle, which are responsible for about 80% of TB infection. The source of the remaining 20% appears to be badgers. Killing badgers in areas where cattle have TB has been shown to bring about a slight reduction in cattle TB in the areas where culling takes place - but also an increase in cattle TB around the edges of those areas. The information on this page needs to be updated and this will be done soon. For more information in the meantime, see the Badger Trust website.
At the heart of the badger culling controversy is the as yet unanswered question - do badgers actually infect cattle with bovine tuberculosis in normal field conditions? On this page, I will look at the arguments for and against.
In the 1960's, when the number of cattle with TB had been reduced to very low figures, it was found that levels of TB in cattle in parts of the south-west were higher than elsewhere. The then Ministry of Agriculture or MAFF (now DEFRA) concluded that the cattle in those areas were not just getting the disease from other cattle. They suspected that there were other sources (or "reservoirs") of TB in those areas, and began to test other animals to see if they had the disease.
In April 1971, a dead badger was found on a farm in Gloucestershire where there had been a recent outbreak of TB. The badger was tested, and found to have the disease. MAFF therefore began to collect and test further dead badgers from Gloucestershire (mainly road traffic casualties), and by April 1973 they had confirmed the presence of bovine TB in 36 out of a total of 165 badgers. Subsequent testing of many hundreds of road casualties across the country has also shown bovine TB to be present in badgers, mainly in those pockets of the south-west of England where TB is most prevalent in cattle.
MAFF also carried out an experiment to find out whether badgers could transmit TB to cattle. Badgers living in a sett which was known to be infected were captured and kept in a yard with healthy calves. The calves eventually developed bovine TB.
In addition, research has shown that badgers can contaminate cattle pasture with tubercle bacilli passed from their bodies in urine and faeces, and that badgers which become very ill with the disease can excrete huge numbers of TB bacilli into the environment. Furthermore, TB bacilli can survive in the environment for anything between a few days and a month, depending on the time of year and other conditions.
More recent research has been able to identify various strains of the Mycobacterium bovis bacteria; and has shown that although badgers and cattle have a number of strains which are unique to each species, there are many more strains which occur in both species.
Thus there is strong circumstantial evidence to suggest that wild badgers may be able to transmit bovine TB to cattle under normal conditions in the countryside.
Many people feel that the evidence against badgers falls short of that which is required to prove beyond reasonable doubt that they are guilty of the charge laid against them. They point out for example that the experiment in which infected badgers passed TB on to healthy cattle took place under artificial conditions, and that there is no direct evidence to show whether, or how, badgers might infect cattle on farmland. Furthermore, in the experiment it was several months before the calves became infected, which shows that even under ideal conditions, the spread of TB from badgers to cattle was by no means straightforward.
As for badgers contaminating the environment with TB bacilli, the facts show that very few badgers are likely to do this. More than 80% of badgers tested for TB have tested negative. The vast majority of the remainder, although infected, were not infectious (in other words, not capable of spreading the disease). Only a very small percentage were found to be infectious.
The fact that badgers with bovine TB have been found in areas where cattle also have the disease proves nothing, as there is no way of telling which species was the source of infection. Given that badgers often forage around cow pats, it is more likely that badgers were infected by cattle rather than the other way around.
Some people have put forward alternative theories to explain why DEFRA (and its predecessor MAFF) has not been able to completely wipe out TB in cattle, theories which do not involve badgers. For example, it is known that the TB test used on cattle is not completely accurate; some cattle with TB are not detected by the test and so escape slaughter. These animals can then transmit the disease to other cattle. It is argued that so long as this hidden reservoir of disease exists in the cattle population, bovine TB can never be wiped out.
It has also been confirmed that recent increases in the number of cattle herds infected with TB, and the spread of the disease to new areas, are due to the spread of infection between cattle, not from badgers. During the Foot and Mouth epidemic, cattle TB tests were suspended, and many cattle were kept together indoors. This enabled infected animals to become infectious and to pass TB onto others. When TB tests resumed after Foot and Mouth restrictions were lifted, they revealed large increases in the number of cattle with the disease. In addition, farmers who lost cattle to the Foot and Mouth slaughter bought in replacement animals from elsewhere, and in many cases these cattle were not tested for TB beforehand. As a result, cattle infected with TB were moved around the country - and so TB has been spread to areas where it has been absent for many years, such as County Durham and parts of Scotland.
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