Mycobacterium bovis | |
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Attenuated strain of M. bovis used in the Bacillus Calmette-Guérin vaccine | |
Scientific classification | |
Domain: | Bacteria |
Phylum: | Actinomycetota |
Class: | Actinomycetia |
Order: | Mycobacteriales |
Family: | Mycobacteriaceae |
Genus: | Mycobacterium |
Species: | M. bovis |
Binomial name | |
Mycobacterium bovis | |
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). It is related to Mycobacterium tuberculosis , the bacterium which causes tuberculosis in humans. M. bovis can jump the species barrier and cause tuberculosis-like infection in humans and other mammals. [2]
The bacteria are curved or straight rods. They sometimes form filaments, which fragment into bacilli or cocci once disturbed. In tissues they form slender rods, straight or curved, or club-shaped. Short, relatively plump bacilli (rods) in tissue smears, large slender beaded rods in culture. They have no flagella or fimbria, and no capsule.[ citation needed ]
Mycobacterium tuberculosis group bacteria are 1.0-4.0 μm long by 0.2-0.3 μm wide in tissues. In culture, they may appear as cocci, or as bacilli up to 6-8 μm long.[ citation needed ]
The bacteria stain Gram-positive, acid-fast. The cell wall contains as high as 60% lipid, giving the mycobacteria their hydrophobic characteristics, slow growth, and resistance to desiccation, disinfectants, acids and antibodies. (Mycobacterium family). They are not easy to stain with aniline dyes; although they are Gram positive, confirming this may be difficult. Ziehl–Neelsen staining results in stain pink with hot carbol fuscin and then resist decolourisation with 3% hydrochloric acid in 95% alcohol (i.e. they are acid-alcohol fast); following washing, the slide is counterstained with e.g. methylene blue.[ citation needed ]
They are nonspore-forming.
M. bovis is a facultative intracellular parasite . For in vitro growth, special culture media are required; for example, Dorset's egg medium incorporates egg yolk, phosphate buffer, magnesium salts, and sodium pyruvate; amino acids may be added, but glycerol is not included, as it is inhibitory. It is inhibited by glycerine. Culture generally requires several weeks at 37 °C to reach colonies visible to the unaided human eye. It is strictly aerobic, and grows at 37, but not at 25 °C. Optimal growth occurs at 37-38 °C. The species does not reduce nitrate or niacin, and is resistant to pyrazinamide. It is sensitive to thiophene-2-carboxylic acid hydrazide.[ citation needed ]
Initially (after 3–4 weeks), its minute, dull flakes, begin to thicken to form dry, irregular masses standing high above the culture medium surface. Eventually, confluent growth is seen over the whole culture surface, forming a rough, waxy blanket, becoming thick and wrinkled and reaching up the sides of the container. Colonies are yellow when first visible, darkening to deep yellow and eventually brick red, if exposed to light. In fluid media, growth is on the surface only, unless a wetting agent (e.g. Tween 80) is added to the medium.[ citation needed ]
M. bovis is similar in structure and metabolism to M. tuberculosis. M. bovis is a Gram-positive, acid-fast, rod-shaped, aerobic bacterium. Unlike M. tuberculosis, M. bovis lacks pyruvate kinase activity, due to pykA containing a point mutation that affects binding of Mg2+ cofactor. [3] Pyruvate kinase catalyses the final step of glycolysis, the dephosphorylation of phosphorenolpyruvate to pyruvate. Therefore, in M. bovis, glycolytic intermediates are unable to enter into oxidative metabolism. Although no specific studies have been performed, M. bovis seemingly must rely on amino acids or fatty acids as an alternative carbon source for energy metabolism.[ citation needed ]
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 or inhaled. [4]
M. bovis is usually transmitted to humans by consuming raw milk from infected cows, although it can also spread via aerosol droplets. Actual infections in humans are nowadays rare in developed countries, mainly because pasteurisation kills M. bovis bacteria in infected milk. In the UK, cattle are tested for the disease as part of an eradication program and culled if they test positive. Such cattle can still enter the human food chain, but only after a meat inspector or a government veterinary surgeon has inspected the carcass and certified that it is fit 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. [5]
Bovine tuberculosis is a chronic infectious disease which affects a broad range of mammalian hosts, including humans, cattle, deer, llamas, pigs, domestic cats, wild carnivores (foxes, coyotes) and omnivores (common brushtail possum, mustelids and rodents); it rarely affects equids or sheep. [6] [7] The disease can be transmitted in several ways; for example, it can be spread 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. [8]
M. bovis is the ancestor of the most widely used vaccine against tuberculosis, M. bovis bacillus Calmette-Guérin (BCG) which was isolated after subculturing on glycerine potato medium 230 times during 13 years starting from an initial virulent strain. [9]
Skin testing is possible in cattle. Casal et al. 2012 tried both recombinant protein and overlapping peptide provocation, finding the peptide test to be less sensitive. [10]
In New Zealand, the introduced common brushtail possum is a vector for the spread of M. bovis. 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 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. [11]
The TB-free New Zealand programme is regarded as "world-leading". [12] 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 cattle controls 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%). [13]
Possums are controlled through a combination of trapping, ground-baiting, and where other methods are impractical, aerial treatment with 1080 poison. [14]
From 1979 to 1984, possum control was stopped due to lack of funding. From that point until 1994, TB rates in herds steadily increased. [15] The area of New Zealand harbouring TB-infected wild animals expanded from about 10% of the country to 40%.[ citation needed ]
The fact that possums are such effective transmitters of TB appears to be facilitated by their behaviour once they get the disease. [16]
In the 1930s, 40% of cattle in the UK were infected with M. bovis and 50,000 new cases of human M. bovis infection were reported every year. [17] According to DEFRA and the Health Protection Agency, the risk to people contracting TB from cattle in Great Britain would be low.[ citation needed ]
Badgers (Meles meles) were first identified as carriers of M. bovis in 1971, but the report of an independent review committee in 1997 (the Krebs Report) concluded: "strong circumstantial evidence [exists] to suggest that badgers represent a significant source of M. bovis infection in cattle... [h]owever, the causal link... has not been proven". [18] In essence, the contribution of badgers 'to the TB problem in British cattle' was at this point a hypothesis that needed to be tested, according to the report. The subsequent Randomised Badger Culling Trial [19] (designed, overseen and analysed by the Independent Scientific Group on Cattle TB, or ISG [20] ) examined this hypothesis by conducting 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, [21] 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 regimens 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." [22]
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 possible maintenance hosts for transmission of bovine TB [23] [24]
In some localised areas, the risk of transmission to cattle from fallow deer has been argued to be greater than it is from badgers. [23] [24]
One of the reasons that the Department for Environment, Food, and Rural Affairs requires infected or suspected cattle to be culled is to meet EU regulations for the export of meat and dairy products to other member states. Meat and dairy products can still be sold in the UK into the human food chain, providing the relevant carcass inspections and milk pasteurisation have been applied. [25] [26]
Spread of the disease to humans by domestic pets became evident in March 2014 when Public Health England announced two people in England developed bTB infections after contact with a domestic cat. The two human cases were linked to 9 cases of bTB infection in cats in Berkshire and Hampshire during 2013. These are the first documented cases of cat-to-human transmission. [27]
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, very little evidence exists 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 no justification for the present test and cull policy in the UK is seen. [28]
In July 2010, the second issue of the discussion document Bovine TB, Time for a Rethink [29] was published by Rethink Bovine TB, an independent research group. The paper considers current policy in England and Wales. It proposes an alternative solution that is both practical and cost effective. In the paper, evidence is drawn from DEFRA and the work by Professors Paul and David Torgerson. [28]
In March 2012, think tank the Bow Group published a target paper urging the government to reconsider its plans to cull thousands of badgers to control bovine TB, stating that the findings of Labour's major badger-culling trials several years prior were that culling does not work. The paper was authored by Graham Godwin-Pearson with a foreword by singer Brian May and contributions by leading tuberculosis scientists, including Lord Krebs. [30] [31] [32]
In 2017, Rachel Tanner and Helen McShane, of the Jenner Institute, Oxford, published research on replacing, reducing, and refining the use of animals in tuberculosis vaccine research. [33]
Cattle can be vaccinated against TB using the BCG vaccine which is used to immunise humans. This is not currently done in UK because the vaccine causes false positives for the current tuberculin test. A new skin test has been developed – Detect Infected among Vaccinated Animals (DIVA) – and phase 1 trials were completed in 2022. [34]
According to Barbara Gutmann Rosenkrantz, the late 19th-century discovery of the relationship between bovine and human tuberculosis led to state and federal attempts to stamp out bovine tuberculosis. The campaigns for clean milk and meat frightened city people into supporting controls, although at the time, little evidence showed that tuberculosis was spread to humans through infected meat or milk. The campaigns against impure meat and milk led to tension between the developing veterinarian profession and the medical profession, each claiming that area as part of their own expertise. [36]
By 1917, 5% of American cattle were infected with M. bovis (bovine tuberculosis or bTB), including 10% dairy animals and 1–2% of beef cattle. The rates were going up. Around 1900, 15,000 Americans, mostly children, died each year from bTB, and many more suffered pain and disfigurement. [37] [38]
Threatened by a sales cutoff ordered by urban public health officials, Vermont state government officials launched an innovative eradication campaign against bTB on farms, 1877 to 1936. They made use of the latest German research, and thereby kept the New York City and Boston markets. [39] Vermont was exceptional, for across the country many farmers strenuously resisted bovine tuberculosis eradication as an expensive violation of their libertarian right to farm. [40]
In recent decades, M. bovis infections in cattle herds in the United States are not common. M. bovis is endemic in white-tailed deer (Odocoileus virginianus) in the northeastern portion of Michigan and northern Minnesota, and sporadically imported from Mexico. Only the white-tailed deer has been confirmed as a maintenance host in the Michigan outbreak of bTB, although other mammals such as raccoons (Procyon lotor), opossums (Didelphis virginiana), and coyotes (Canis latrans) can serve as spill-over and dead-end hosts. [41] The fact that white-tailed deer are a maintenance host for M. bovis remains a significant barrier to the US nationwide eradication of the disease in livestock. In 2008, 733,998 licensed deer hunters harvested around 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. [42]
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 a 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, affected wild elk and white-tailed deer are found in and around Riding Mountain National Park in Manitoba. To improve control and eliminate bTB, the Canadian Food Inspection Agency has split Manitoba into two management areas: The Riding Mountain TB eradication area, where the disease has been found, and the Manitoba TB Eradication Area, the rest of the province outside RMEA where the disease has not been found. [43] The disease has also been found in African buffalo in South Africa.[ citation needed ]
M. bovis can be transmitted from human to human; an outbreak occurred in Birmingham, England, in 2004, [44] and from human to cattle, [45] [46] but such occurrences are rare.
In Mexico, the disease is prevalent and rising among humans. [47]
The infection of humans with M. bovis is referred to as zoonotic tuberculosis. [48] In 2017, the World Health Organization (WHO), World Organization for Animal Health (OIE), Food and Agriculture Organization (FAO), and The International Union Against Tuberculosis and Lung Disease (The Union), published the first Roadmap for Zoonotic Tuberculosis, recognizing zoonotic tuberculosis as a prominent global health problem. [49] The main route of transmission is through the consumption of unpasteurized milk or other dairy products, although transmission via inhalation and via consumption of poorly cooked meat has also been reported. [49] In 2018, based on the most recent Global Tuberculosis Report, an estimated 142,000 new cases of zoonotic tuberculosis, and 12,500 deaths due to the disease occurred. [50] Cases of zoonotic tuberculosis have been reported in Africa, the Americas, Europe, the Eastern Mediterranean, and the Western Pacific. [51] Human zoonotic tuberculosis cases are linked to the presence of bovine tuberculosis in cattle, and regions without adequate disease control measures and/or disease surveillance are at higher risk. [51] It is difficult to clinically distinguish zoonotic tuberculosis from tuberculosis caused by Mycobacterium tuberculosis in people, and the current most commonly used diagnostics cannot effectively distinguish between M. bovis and M. tuberculosis, which contributes to an underestimation of total cases worldwide. [52] Controlling this disease requires animal health, food safety, and human health sectors to work together under a One Health approach (multi-disciplinary collaborations to improve the health of animals, people, and the environment). [53]
The 2017 Roadmap identified ten priority areas for addressing zoonotic tuberculosis, which include collecting more accurate data, improving diagnostics, closing research gaps, improving food safety, reducing M. bovis in animal populations, identifying risk factors for transmission, increasing awareness, developing policies, implementing interventions, and increasing investments. [49] To align with goals outlined in the Stop TB Partnership Global Plan to End TB 2016-2020, [54] The Roadmap outlines specific milestones and goals to be met within this time frame. [49]
M. bovis is innately resistant to pyrazinamide, so the standard human treatment is isoniazid and rifampicin for 9 months. [55] Most cattle that test positive are killed. [56]
The Bacillus Calmette–Guérin (BCG) vaccine is a vaccine primarily used against tuberculosis (TB). It is named after its inventors Albert Calmette and Camille Guérin. In countries where tuberculosis or leprosy is common, one dose is recommended in healthy babies as soon after birth as possible. In areas where tuberculosis is not common, only children at high risk are typically immunized, while suspected cases of tuberculosis are individually tested for and treated. Adults who do not have tuberculosis and have not been previously immunized, but are frequently exposed, may be immunized, as well. BCG also has some effectiveness against Buruli ulcer infection and other nontuberculous mycobacterial infections. Additionally, it is sometimes used as part of the treatment of bladder cancer.
Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in which case it is known as latent tuberculosis. Around 10% of latent infections progress to active disease that, if left untreated, kill about half of those affected. Typical symptoms of active TB are chronic cough with blood-containing mucus, fever, night sweats, and weight loss. Infection of other organs can cause a wide range of symptoms.
Q fever or query fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period can range from 9 to 40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.
Babesiosis or piroplasmosis is a malaria-like parasitic disease caused by infection with a eukaryotic parasite in the order Piroplasmida, typically a Babesia or Theileria, in the phylum Apicomplexa. Human babesiosis transmission via tick bite is most common in the Northeastern and Midwestern United States and parts of Europe, and sporadic throughout the rest of the world. It occurs in warm weather. People can get infected with Babesia parasites by the bite of an infected tick, by getting a blood transfusion from an infected donor of blood products, or by congenital transmission . Ticks transmit the human strain of babesiosis, so it often presents with other tick-borne illnesses such as Lyme disease. After trypanosomes, Babesia is thought to be the second-most common blood parasite of mammals. They can have major adverse effects on the health of domestic animals in areas without severe winters. In cattle, the disease is known as Texas cattle fever or redwater.
Mycobacterium tuberculosis, also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid. This coating makes the cells impervious to Gram staining, and as a result, M. tuberculosis can appear weakly Gram-positive. Acid-fast stains such as Ziehl–Neelsen, or fluorescent stains such as auramine are used instead to identify M. tuberculosis with a microscope. The physiology of M. tuberculosis is highly aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian respiratory system, it infects the lungs. The most frequently used diagnostic methods for tuberculosis are the tuberculin skin test, acid-fast stain, culture, and polymerase chain reaction.
Mycobacterium is a genus of over 190 species in the phylum Actinomycetota, assigned its own family, Mycobacteriaceae. This genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and leprosy in humans. The Greek prefix myco- means 'fungus', alluding to this genus' mold-like colony surfaces. Since this genus has cell walls with a waxy lipid-rich outer layer containing high concentrations of mycolic acid, acid-fast staining is used to emphasize their resistance to acids, compared to other cell types.
Brucellosis is a zoonosis caused by ingestion of unpasteurized milk from infected animals, or close contact with their secretions. It is also known as undulant fever, Malta fever, and Mediterranean fever.
Paratuberculosis is a contagious, chronic and sometimes fatal infection that primarily affects the small intestine of ruminants. It is caused by the bacterium Mycobacterium avium subspecies paratuberculosis. Infections normally affect ruminants, but have also been seen in a variety of nonruminant species, including rabbits, foxes, and birds. Horses, dogs, and nonhuman primates have been infected experimentally. Paratuberculosis is found worldwide, with some states in Australia being the only areas proven to be free of the disease. At least in Canada, the signs of BJD usually start when cattle are four to seven years of age, and then usually only are diagnosed in one animal at a time. Cattle "with signs of Johne’s disease shed billions of bacteria through their manure and serve as a major source of infection for future calves."
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals that have been exposed to infected birds; in these cases, symptoms are frequently severe or fatal.
Campylobacter fetus is a rod-shaped, gram-negative species of bacteria within the genus Campylobacter of phylum Pseudomonadota. Identification of C. fetus species in infected animals or people is routinely performed by culture on blood or cefoperazone deoxycholate agar. Subspecies of C. fetus commonly causes reproductive disease in ruminants and gastrointestinal disease in humans. Transmission of C. fetus subspecies venerealis occurs mainly through venereal contact while transmission of C. fetus subspecies fetus occurs mainly through ingestion of bacteria in a contaminated environment. Infertility in cattle and abortion in sheep are common outcomes of infection associated with C. fetus subspecies venerealis and C. fetus subspecies fetus, respectively. Disease in humans occurs through zoonotic transmission of C. fetus mainly via ingestion of contaminated food or water sources. C. fetus can be diagnosed with polymerase chain reaction assays, enzyme linked immunosorbent assays and vaginal mucus agglutination testing. As vaccines are typically not efficient in preventing future spread, infected bulls are often culled. Human infections may be treated with erythromycin as antimicrobial resistance has been emerging for the fluoroquinolones.
Bovine alphaherpesvirus 1 (BoHV-1) is a virus of the family Herpesviridae and the subfamily Alphaherpesvirinae, known to cause several diseases worldwide in cattle, including rhinotracheitis, vaginitis, balanoposthitis, abortion, conjunctivitis, and enteritis. BoHV-1 is also a contributing factor in shipping fever, also known as bovine respiratory disease (BRD). It is spread horizontally through sexual contact, artificial insemination, and aerosol transmission and it may also be transmitted vertically across the placenta. BoHV-1 can cause both clinical and subclinical infections, depending on the virulence of the strain. Although these symptoms are mainly non-life-threatening it is an economically important disease as infection may cause a drop in production and affect trade restrictions. Like other herpesviruses, BoHV-1 causes a lifelong latent infection and sporadic shedding of the virus. The sciatic nerve and trigeminal nerve are the sites of latency. A reactivated latent carrier is normally the source of infection in a herd. The clinical signs displayed are dependent on the virulence of the strain. There is a vaccine available which reduces the severity and incidence of disease. Some countries in Europe have successfully eradicated the disease by applying a strict culling policy.
Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by Romanian bacteriologist Victor Babeș in 1888; over 100 species of Babesia have since been identified.
Bovine viral diarrhea (BVD), bovine viral diarrhoea or mucosal disease, previously referred to as bovine virus diarrhea (BVD), is an economically significant disease of cattle that is found in the majority of countries throughout the world. Worldwide reviews of the economically assessed production losses and intervention programs incurred by BVD infection have been published. The causative agent, bovine viral diarrhea virus (BVDV), is a member of the genus Pestivirus of the family Flaviviridae.
Mycobacterium africanum is a species of Mycobacterium that is most commonly found in West African countries, where it is estimated to cause up to 40% of pulmonary tuberculosis. The symptoms of infection resemble those of M. tuberculosis.
Mycobacterium caprae is a species of bacteria in the genus Mycobacterium and a member of the Mycobacterium tuberculosis complex. The species is named after the caprines, the organisms from which M. caprae was first isolated. Prior to 2003, the species was referred to as Mycobacterium tuberculosis subsp. caprae. It is also synonymous with the name Mycobacterium bovis subsp. caprae.
Bovine leukemia virus (BLV) is a retrovirus which causes enzootic bovine leukosis in cattle. It is closely related to the human T‑lymphotropic virus type 1 (HTLV-I). BLV may integrate into the genomic DNA of B‑lymphocytes as a DNA intermediate, or exist as unintegrated circular or linear forms. Besides structural and enzymatic genes required for virion production, BLV expresses the Tax protein and microRNAs involved in cell proliferation and oncogenesis. In cattle, most infected animals are asymptomatic; leukemia is rare, but lymphoproliferation is more frequent (30%).
The common brushtail possum was introduced from Australia to New Zealand, where it has become invasive and a major agricultural and conservation pest.
Dairy farming in New Zealand began during the early days of colonisation by Europeans. The New Zealand dairy industry is based almost exclusively on cattle, with a population of 4.92 million milking cows in the 2019–20 season. The income from dairy farming is now a major part of the New Zealand economy, becoming an NZ$13.4 billion industry by 2017.
Badger culling in the United Kingdom is permitted under licence, within a set area and timescale, as a way to reduce badger numbers in the hope of controlling the spread of bovine tuberculosis (bTB). Humans can catch bTB, but public health control measures, including milk pasteurisation and the BCG vaccine, mean it is not a significant risk to human health. The disease affects cattle and other farm animals, some species of wildlife including badgers and deer, and some domestic pets such as cats. Geographically, bTB has spread from isolated pockets in the late 1980s to cover large areas of the west and south-west of England and Wales in the 2010s. Some people believe this correlates with the lack of badger control.
Anaplasma bovis is gram negative, obligate intracellular organism, which can be found in wild and domestic ruminants, and potentially a wide variety of other species. It is one of the last species of the Family Anaplasmaceae to be formally described. It preferentially infects host monocytes, and is often diagnosed via blood smears, PCR, and ELISA. A. bovis is not currently considered zoonotic, and does not frequently cause serious clinical disease in its host. This organism is transmitted by tick vectors, so tick bite prevention is the mainstay of A. bovis control, although clinical infections can be treated with tetracyclines. This organism has a global distribution, with infections noted in many areas, including Korea, Japan, Europe, Brazil, Africa, and North America.