Mycobacterium bovis
Encyclopedia
Mycobacterium bovis is a slow-growing (16 to 20 hour generation time), aerobic
bacterium and the causative agent of tuberculosis
in cattle
(known as bovine TB). Related to M. tuberculosis
—the bacterium which causes tuberculosis in humans—M. bovis can also jump the species barrier
and cause tuberculosis in humans.
M. bovis is usually transmitted to humans via infected milk, although it can also spread via aerosol droplets. Actual infections in humans are rare, mostly due to pasteurisation killing any bacteria in infected milk; as well, cattle are randomly tested for the disease and immediately culled if infected, but can still be used for human consumption. However, in areas of the developing world where pasteurisation is not routine, M. bovis is a relatively common cause of human tuberculosis.
Bovine TB is a chronic infectious disease which affects a broad range of mammalian hosts including humans, cattle
, deer
, llamas, pigs
, domestic cats, wild carnivores (fox
, coyotes, badgers), possums, mustelids and rodents; it rarely affects equids or sheep. The disease can be transmitted in several ways, for example, badgers excrete M. bovis in exhaled air, sputum, urine, faeces and pus, so the disease can be transmitted by direct contact, contact with the excreta of an infected animal, or inhalation of aerosols, depending on the species involved.
, the common brushtail possum
is the main vector
for the spread of M. bovis. The disease now endemic in possums across approximately 38% of New Zealand (known as ‘vector risk areas’). In these areas, nearly 70% of new herd infections can be traced back to possums or ferrets. The Biosecurity Act 1993
, which established a National Pest Management Strategy, is the legislation behind control of the disease in New Zealand. The Animal Health Board
(AHB) operates a nationwide programme of cattle testing and possum control, with the goal of eradicating M. bovis from wild vector species across 2.5 million hectares – or one quarter – of New Zealand’s at-risk areas, by 2026 and, eventually, eradicating the disease entirely.
The TBfree New Zealand programme is regarded as "world-leading". It has successfully reduced cattle and deer herd infection rates from more than 1700 in 1994 to fewer than 100 herds in July 2011. Much of this success can be attributed to sustained possum control reducing cross-infection and breaking the disease cycle. For example, at Hohotaka, in New Zealand's central North Island
, control work from 1988 to 1994 achieved a sustained mean reduction of 87.5% in the density of TB‐infected possums. As expected, annual TB incidence in local cattle herds consequently declined by a similar amount (83.4%).
Possums are controlled through a combination of trapping
, ground-baiting and, where other methods are impractical, aerial treament with 1080 poison.
From 1979 - 1984, possum control was stopped due to lack of funding. In spite of regular and frequent TB testing of cattle herds, the number of infected herds snowballed and continued to increase until 1994. The area of New Zealand where there were TB wild animals expanded from about 10 to 40%.
That possums are such effective transmitters of TB appears to be facilitated by their behaviour once they succumb to the disease. Terminally ill TB possums will show increasingly erratic behaviour, such as venturing out during the daytime to get enough food to eat, and seeking out buildings in which to keep warm. As a consequence, they may wander on to paddocks, where they naturally attract the attention of inquisitive cattle and deer. This behaviour has been captured on video.
Badgers (Meles meles) were first identified as carriers of M. bovis 30 years ago, but the report of an independent review committee in 1997 concluded badgers made an important contribution to the spread of M. bovis between herds of cattle. This was the major cause of the current battle between animal conservationists (keen to save the badger) and farmers (keen to cull badgers, to reduce livestock losses). The Randomised Badger Culling Trial (designed, overseen and analysed by the Independent Scientific Group on Cattle TB, or ISG ) was a large field trial of widescale (proactive) culling and localised reactive culling (in comparison with areas which received no badger culling). In their final report, the ISG concluded: "First, while badgers are clearly a source of cattle TB, careful evaluation of our own and others’ data indicates that badger culling can make no meaningful contribution to cattle TB control in Britain. Indeed, some policies under consideration are likely to make matters worse rather than better. Second, weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of disease in all areas where TB occurs, and in some parts of Britain are likely to be the main source of infection. Scientific findings indicate that the rising incidence of disease can be reversed, and geographical spread contained, by the rigid application of
cattle-based control measures alone." On 26 July 2007, the Minister of State, Department for Environment, Food and Rural Affairs (Lord Rooker) said "My Lords, we welcome the Independent Scientific Group’s final report, which further improves the evidence base. We are carefully considering the issues that the report raises, and will continue to work with industry, government advisers and scientific experts in reaching policy decisions on these issues."
In the UK, many other mammals have been found to be infected with M. bovis, although the frequency of isolation is generally much less than cattle and badgers. In some areas of South-West England, deer
, especially fallow deer
due to their gregarious behaviour, have been implicated as a possible maintenance host for transmission of bovine TB, a disease which in the UK in 2005 cost £90 million in attempts to eradicate. It has been argued that in some localised areas, the risk of transmission to cattle from fallow deer is greater than it is from badgers.
In a 2010 opinion piece in Trends in Microbiology, Paul and David Torgerson argued that bovine tuberculosis is a negligible public health problem in the UK, providing milk is pasteurized. Bovine TB is very rarely spread by aerosol from cattle to humans. Therefore, the bovine tuberculosis control programme in the UK in its present form is a misallocation of resources and provides no benefit to society. Indeed, there is even very little evidence of a positive cost benefit to the livestock industry, as few studies have been undertaken on the direct costs of bovine TB to animal production. Milk pasteurisation was the single public health intervention that prevented the transmission of bovine TB to humans, and there is no justification for the present test and cull policy in the UK.
(Odocoileus virginianus) in the northeastern portion of the state of Michigan
and in northern Minnesota, and sporadic import of the disease from Mexico. The white-tailed deer has been confirmed as the sole maintenance host in the Michigan outbreak of bovine tuberculosis which remains a significant barrier to the US nationwide eradication of the disease in livestock. In 2008, 733,998 licensed deer hunters harvested approximately 489,922 white-tailed deer in attempts to control the disease spread. These hunters purchased more than 1.5 million deer harvest tags. The economic value of deer hunting to Michigan’s economy in the drive to eradicate TB is substantial. For example, in 2006, hunters spent US$507 million hunting white-tailed deer in Michigan.
Mycobacterium bovis can be transmitted from human to human; there was an outbreak in Birmingham
, England
in 2004, and from human to cattle, but such occurrences are rare.
M. bovis is innately resistant to pyrazinamide
: therefore the standard treatment is isoniazid
and rifampicin
for 9 months.
However, most cattle with TB will be culled.
Aerobic organism
An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...
bacterium and the causative agent of tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
in cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
(known as bovine TB). Related to M. tuberculosis
Mycobacterium tuberculosis
Mycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...
—the bacterium which causes tuberculosis in humans—M. bovis can also jump the species barrier
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
and cause tuberculosis in humans.
Pathogenesis
During the first half of the 20th century, M. bovis is estimated to have been responsible for more losses among farm animals than all other infectious diseases combined. Infection occurs if the bacterium is ingested.M. bovis is usually transmitted to humans via infected milk, although it can also spread via aerosol droplets. Actual infections in humans are rare, mostly due to pasteurisation killing any bacteria in infected milk; as well, cattle are randomly tested for the disease and immediately culled if infected, but can still be used for human consumption. However, in areas of the developing world where pasteurisation is not routine, M. bovis is a relatively common cause of human tuberculosis.
Bovine TB is a chronic infectious disease which affects a broad range of mammalian hosts including humans, cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
, deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
, llamas, pigs
PIGS
PIGS is a four letter acronym that can stand for:* PIGS , Phosphatidylinositol glycan anchor biosynthesis, class S, a human gene* PIGS , the economies of Portugal, Italy , Greece and Spain...
, domestic cats, wild carnivores (fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
, coyotes, badgers), possums, mustelids and rodents; it rarely affects equids or sheep. The disease can be transmitted in several ways, for example, badgers excrete M. bovis in exhaled air, sputum, urine, faeces and pus, so the disease can be transmitted by direct contact, contact with the excreta of an infected animal, or inhalation of aerosols, depending on the species involved.
New Zealand
In New ZealandNew Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, the common brushtail possum
Common Brushtail Possum
The Common Brushtail Possum is a nocturnal, semi-arboreal marsupial of the family Phalangeridae, it is native to Australia, and the largest of the possums.Like most possums, the Common Brushtail is nocturnal...
is the main vector
Vector (dispersal)
In the biology of dispersal, a dispersal vector is "an agent transporting seeds or other dispersal units". Dispersal vectors may include biotic factors, such as animals, or abiotic factors, such as the wind....
for the spread of M. bovis. The disease now endemic in possums across approximately 38% of New Zealand (known as ‘vector risk areas’). In these areas, nearly 70% of new herd infections can be traced back to possums or ferrets. The Biosecurity Act 1993
Biosecurity Act 1993
Biosecurity Act 1993 is an Act of Parliament in New Zealand passed in order to prevent pests and other unwanted organisms. It was a world first.Part 5 of the Act provides for a National Pest Management Strategy and Regional Pest Management Strategy....
, which established a National Pest Management Strategy, is the legislation behind control of the disease in New Zealand. The Animal Health Board
Animal Health Board (New Zealand)
The Animal Health Board commonly known by its acronym, AHB, is an incorporated society, legally responsible for managing and implementing the National Pest Management Strategy for bovine tuberculosis in New Zealand. Its powers derive from the Biosecurity Act 1993 and its mission is to eradicate...
(AHB) operates a nationwide programme of cattle testing and possum control, with the goal of eradicating M. bovis from wild vector species across 2.5 million hectares – or one quarter – of New Zealand’s at-risk areas, by 2026 and, eventually, eradicating the disease entirely.
The TBfree New Zealand programme is regarded as "world-leading". It has successfully reduced cattle and deer herd infection rates from more than 1700 in 1994 to fewer than 100 herds in July 2011. Much of this success can be attributed to sustained possum control reducing cross-infection and breaking the disease cycle. For example, at Hohotaka, in New Zealand's central North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
, control work from 1988 to 1994 achieved a sustained mean reduction of 87.5% in the density of TB‐infected possums. As expected, annual TB incidence in local cattle herds consequently declined by a similar amount (83.4%).
Possums are controlled through a combination of trapping
Trapping
Trapping may refer to:* Animal trapping, the remote capture of animals* Trapping , a fighting technique and range* Trap , a color management technique* Mantrap, a security device...
, ground-baiting and, where other methods are impractical, aerial treament with 1080 poison.
From 1979 - 1984, possum control was stopped due to lack of funding. In spite of regular and frequent TB testing of cattle herds, the number of infected herds snowballed and continued to increase until 1994. The area of New Zealand where there were TB wild animals expanded from about 10 to 40%.
That possums are such effective transmitters of TB appears to be facilitated by their behaviour once they succumb to the disease. Terminally ill TB possums will show increasingly erratic behaviour, such as venturing out during the daytime to get enough food to eat, and seeking out buildings in which to keep warm. As a consequence, they may wander on to paddocks, where they naturally attract the attention of inquisitive cattle and deer. This behaviour has been captured on video.
United Kingdom
In the 1930s, 40% of cows in the UK were infected with M. bovis and there were 50,000 new cases of human M. bovis infection every year. According to DEFRA and the Health Protection Agency, the risk to people contracting TB from cattle in Great Britain today is very low. The HPA has said that three quarters of the 440 human cases reported to the HPA between 1994 and 2006 were aged 50 years and above and only 44 cases (16%) were known to be non-UK born.Badgers (Meles meles) were first identified as carriers of M. bovis 30 years ago, but the report of an independent review committee in 1997 concluded badgers made an important contribution to the spread of M. bovis between herds of cattle. This was the major cause of the current battle between animal conservationists (keen to save the badger) and farmers (keen to cull badgers, to reduce livestock losses). The Randomised Badger Culling Trial (designed, overseen and analysed by the Independent Scientific Group on Cattle TB, or ISG ) was a large field trial of widescale (proactive) culling and localised reactive culling (in comparison with areas which received no badger culling). In their final report, the ISG concluded: "First, while badgers are clearly a source of cattle TB, careful evaluation of our own and others’ data indicates that badger culling can make no meaningful contribution to cattle TB control in Britain. Indeed, some policies under consideration are likely to make matters worse rather than better. Second, weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of disease in all areas where TB occurs, and in some parts of Britain are likely to be the main source of infection. Scientific findings indicate that the rising incidence of disease can be reversed, and geographical spread contained, by the rigid application of
cattle-based control measures alone." On 26 July 2007, the Minister of State, Department for Environment, Food and Rural Affairs (Lord Rooker) said "My Lords, we welcome the Independent Scientific Group’s final report, which further improves the evidence base. We are carefully considering the issues that the report raises, and will continue to work with industry, government advisers and scientific experts in reaching policy decisions on these issues."
In the UK, many other mammals have been found to be infected with M. bovis, although the frequency of isolation is generally much less than cattle and badgers. In some areas of South-West England, deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
, especially fallow deer
Fallow Deer
The Fallow Deer is a ruminant mammal belonging to the family Cervidae. This common species is native to western Eurasia, but has been introduced widely elsewhere. It often includes the rarer Persian Fallow Deer as a subspecies , while others treat it as an entirely different species The Fallow...
due to their gregarious behaviour, have been implicated as a possible maintenance host for transmission of bovine TB, a disease which in the UK in 2005 cost £90 million in attempts to eradicate. It has been argued that in some localised areas, the risk of transmission to cattle from fallow deer is greater than it is from badgers.
In a 2010 opinion piece in Trends in Microbiology, Paul and David Torgerson argued that bovine tuberculosis is a negligible public health problem in the UK, providing milk is pasteurized. Bovine TB is very rarely spread by aerosol from cattle to humans. Therefore, the bovine tuberculosis control programme in the UK in its present form is a misallocation of resources and provides no benefit to society. Indeed, there is even very little evidence of a positive cost benefit to the livestock industry, as few studies have been undertaken on the direct costs of bovine TB to animal production. Milk pasteurisation was the single public health intervention that prevented the transmission of bovine TB to humans, and there is no justification for the present test and cull policy in the UK.
United States of America
In the United States, there is endemic M. bovis in white-tailed deerWhite-tailed Deer
The white-tailed deer , also known as the Virginia deer or simply as the whitetail, is a medium-sized deer native to the United States , Canada, Mexico, Central America, and South America as far south as Peru...
(Odocoileus virginianus) in the northeastern portion of the state of Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
and in northern Minnesota, and sporadic import of the disease from Mexico. The white-tailed deer has been confirmed as the sole maintenance host in the Michigan outbreak of bovine tuberculosis which remains a significant barrier to the US nationwide eradication of the disease in livestock. In 2008, 733,998 licensed deer hunters harvested approximately 489,922 white-tailed deer in attempts to control the disease spread. These hunters purchased more than 1.5 million deer harvest tags. The economic value of deer hunting to Michigan’s economy in the drive to eradicate TB is substantial. For example, in 2006, hunters spent US$507 million hunting white-tailed deer in Michigan.
Global
The disease is found in cattle throughout the globe, but some countries have been able to reduce or limit the incidence of the disease through process of 'test and cull' of the cattle stock. Most of Europe and several Caribbean countries (including Cuba) are virtually free of M. bovis. Australia is officially free of the disease since the successful BTEC program, but residual infections might exist in feral water buffalo in isolated parts of the Northern Territory. In Canada, there are affected wild elk and white-tailed deer in and around Riding Mountain National Park in Manitoba. To improve control and eliminate bovine TB, the Canadian Food Inspection Agency (CFIA) has split Manitoba into two management areas: The Riding Mountain TB eradication area (RMEA), the area where the disease has been found and the Manitoba TB Eradication Area (MTEA), the rest of the province outside RMEA where the disease has not been found. The disease has also been found in wild buffalo in South Africa.Mycobacterium bovis can be transmitted from human to human; there was an outbreak in Birmingham
Birmingham
Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 2004, and from human to cattle, but such occurrences are rare.
Treatment
- See: Tuberculosis treatmentTuberculosis treatmentTuberculosis treatment refers to the medical treatment of the infectious disease tuberculosis .The standard "short" course treatment for TB is isoniazid, rifampicin , pyrazinamide, and ethambutol for two months, then isoniazid and rifampicin alone for a further four months...
M. bovis is innately resistant to pyrazinamide
Pyrazinamide
Pyrazinamide is a drug used to treat tuberculosis. The drug is largely bacteriostatic, but can be bacteriocidal on actively replicating tuberculosis bacteria.-Abbreviations:...
: therefore the standard treatment is isoniazid
Isoniazid
Isoniazid , also known as isonicotinylhydrazine , is an organic compound that is the first-line antituberculosis medication in prevention and treatment. It was first discovered in 1912, and later in 1951 it was found to be effective against tuberculosis by inhibiting its mycolic acid...
and rifampicin
Rifampicin
Rifampicin or rifampin is a bactericidal antibiotic drug of the rifamycin group. It is a semisynthetic compound derived from Amycolatopsis rifamycinica ...
for 9 months.
However, most cattle with TB will be culled.
External links
- TB free New Zealand - TB control programme in New Zealand
- Bovine TB information on Department of Conservation website - The use of 1080 for pest control in New Zealand - Possums as reservoirs of bovine tuberculosis
- Information about bovine TB on 1080: The Facts website - Facts about how 1080 poison is used to control bovine TB in New Zealand