Bovine TB: What is bovine tuberculosis?
Bovine tuberculosis (bTB)‘Tuberculosis’ (TB) is a serious disease of warm-blooded animals arising from infection by organisms of the Mycobacterium tuberculosis (MTB) complex. This is a group of closely related bacteria that includes:
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Other bacteria that occasionally cause TB in humans and animals. The MTB complex itself is part of a family of more than 80 different bacterial species known as Mycobacteriaceae. Many of these bacteria are harmless to animals and people, but others are responsible for diseases such as:
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| Cattle, buffalo and bison, are the natural host of M. bovis, but nearly all warm-blooded animals are susceptible to the infection. In fact, compared to other bacteria of the MTB complex, M. bovis has a very broad range of animal hosts. This complicates the control of bovine TB, particularly when the infection becomes self-sustaining in wildlife species, which in turn can become reservoirs of M. bovis for domestic animals. |
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This site gives more information on what measures the Government is taking to try and control bovine TB and what further work is being carried out to better understand the disease.
Human infection with M. bovis can also cause TB that is clinically
and pathologically indistinguishable from that caused by M. tuberculosis.
However, in developed countries TB in humans arises principally
from infection with M. tuberculosis, which is generally transmitted
from person to person through the air by sneezing or coughing. The risk
of people contracting TB from cattle in Great Britain is considered very
low. At present, less than 1% of all confirmed cases of TB in humans are
due to infection with M. bovis. This is similar to the situation
reported in the vast majority of developed countries.
There are a number of measures now in place to ensure that the risk of
M. bovis being transmitted to humans remains low. More information
can be found on our public health pages.
More information on human TB can be found on the following websites:
Historical Overview of bovine TB
During the 1930s, a large proportion of dairy cows were infected with M. bovis. Many were kept near large cities to provide urban dwellers with fresh milk and most were closely confined, in poorly ventilated cowsheds, which are ideal conditions for the disease to spread. Many infected cows developed TB in the udders and shed M. bovis in the milk. Because most milk was drunk raw (untreated), milk-borne human M. bovis infection was a major public health risk and an important source of TB in humans. During this time, over 50,000 new cases of human TB were recorded each year in Great Britain and it was estimated that 2,500 people were dying annually from TB caused by M. bovis.
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To try to control the problem, in 1935 the Government introduced a voluntary TB testing scheme for cattle. Any animals that were positive to these tests were slaughtered. To try to stop bTB spreading to other herds, cattle were not allowed to be moved from farms affected with bTB. This testing and slaughter programme became compulsory in 1950 and by 1980 it had reduced the national incidence of TB in cattle to a very low level. In addition to this, routine pasteurisation (heat treatment) of cows’ milk and inspection of cattle carcases at slaughterhouses were gradually put in place to further protect public health. |
Although the incidence of bTB has increased over the last 15 years, the testing and slaughter programme remains central to our strategy to stop its spread.
In November 2004 we introduced enhanced testing and control measures to help improve the detection of bTB, so that action can be taken quickly to prevent the spread of the disease. More information can be found on the November 2004 measures.
A ten-year Government strategic framework for the sustainable control of bovine tuberculosis in Great Britain was published in March 2005. Through this framework Government aims to bring about a sustainable improvement in control of bTB over the next 10 years.
In December 2005, we also announced pre-movement testing in England and Wales to help reduce the risk of bTB spreading between herds. More information can be found on the testing pages of this website.
The Government is committed to finding the best way to combat bTB, backed by robust evidence. Our wide-ranging programme of research continues to support this aim. More information can be found on the Research & Development pages of this website.
How is bovine TB spread?
There is still some uncertainty surrounding bTB and the way it is transmitted. Bovine TB is spread primarily through the exchange of respiratory secretions between infected and uninfected animals. This transmission usually happens when animals are in close contact with each other. Thus, animal density plays a major factor in the transmission of M. bovis. Bacteria released into the air through coughing and sneezing can spread the disease to uninfected animals.
Bovine TB is a chronic disease and it can take years to develop. M. bovis grows very slowly and only replicates every 12-20 hours. The lymph nodes in the animal’s head usually show infection first and as the disease progresses lesions will begin to develop on the surface of the lungs and chest cavity.
Due to the slow progression of infection, the clinical signs of bTB, such as weakness, coughing and loss of weight, are now rarely seen in cattle in GB. The Government’s compulsory testing and slaughter programme ensures that most cattle herds are tested for bTB at least every four years. This identifies most infected cattle before the disease is apparent.
Suspect clinical signs and lesions of TB in cattle are notifiable to the Divisional Veterinary Manager (DVM) of Animal Health (formerly SVS).
Cattle to cattle spread
Cattle to cattle transmission is a serious cause of disease spread which is substantiated by scientific evidence, most recently in Nature (Gilbert, M et al. Cattle movements and bovine tuberculosis in Great Britain. Nature volume 435, pages 491-496 (2005)) and Veterinary Records (Gopal, R et al. Introduction of bovine tuberculosis to north-east England by bought-in cattle. Veterinary Record 159, pages 265-271 (2006)).
In November 2004, we announced enhanced testing and control measures designed to keep clean areas clean and help prevent further spread of bTB. These included changes to testing frequency and imposition of movement restrictions immediately a test becomes overdue. More information can be found on the November 2004 measures.
New legislation regarding the compulsory pre-movement testing of cattle came into force in England on 27 March 2006, with the aim of reducing the spread of bTB between herds in high risk areas and to areas free from disease. It is now a statutory requirement that all cattle over 42 days old moving out of a 1 or 2 yearly tested herd must have tested negative to a TB test within 60 days prior to movement unless the herd or movement meets an exemption. More information can be found on our pre-movement testing pages.
Spread between badgers and cattle
The evidence for a link between bTB in badgers and bTB in cattle was reviewed in 1997 by the Independent Scientific Review Group, led by Professor John Krebs. The Executive Summary of the Group's findings and recommendations is available on the Defra website.
The Krebs group concluded that:
"the sum of evidence strongly supports the view that, in Britain, badgers were a significant source of infection in cattle... It is not, however, possible to state quantitatively what contribution badgers make to cattle infection"
The groups recognised however, that scientific data were lacking and recommended that an experiment, the Randomised Badger Culling Trial (RBCT), be set up to establish the effect of culling badgers on TB in cattle.
Page last modified:
22 May 2007