Bovine Tuberculosis

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Contents

What is Bovine Tuberculosis?

Bovine tuberculosis is a disease caused by a bacterium called Mycobacterium bovis. Bovine TB is found most commonly in cattle but is also prominent in domestic herds throughout the country <ref>Thidodeaux, W. 2013, What is Bovine Tuberculosis?, eHow health, Respiratory Disorders Sourced on 7/09/2013 can be found at http://www.ehow.com/about_5032766_bovine-tuberculosis.html </ref>. The bacteria its self is slow growing and aerobic in nature, during the early 20th century Bovine TB was responsible for more losses of livestock animals than all of the other infectious diseases combined <ref>USDA. 2009. Assessment of Pathways for the Introduction and Spread of Mycobacterium bovis in the United States, 2009 USDA–APHIS–VS–CEAH. Fort Collins, CO Avaliable online from http://www.aphis.usda.gov/animal_health/emergingissues/downloads/bovine_tb_pathways_2009030711.pdf </ref>.This disease was first brought to New Zealand in the cattle brought over by the early European settlers in the 19th century <ref>de Lisle, G.W. 1993, Bovine tuberculosis – the New Zealand problem. Proceedings of the New Zealand Grassland Association 55, pp. 199-202. </ref>. By the 1940’s the bacteria had become a serious problem, with reductions in productivity and by putting people’s health and lives <ref>Department of Conservation (2013) About DoC http://www.doc.govt.nz/about-doc/[Accessed 22/09/13]. </ref>.

Why it is an issue

Symptoms arise from the formation of bovine tuberculosis nodules in the lungs or chest cavity. The primary symptoms of Bovine TB infection include persistent coughing, weakness and loss of weight <ref>Defra 2013, About bovine TB. Department for Environment Food and Rural Affairs, http://www.defra.gov.uk/animal-diseases/a-z/about bovine-tb downloaded 17/09/2013. </ref>, as well as death in extreme cases <ref>Animal Health Board and Department of Conservation (2003), (W. Green, Ed), The use of 1080 to control possums and other pests – A resource document, Animal Health Board and Department of Conservation, Wellington, New Zealand, (AHB and DOC)</ref> Bovine TB is transmitted by direct physical contact, aerosol droplets from coughing, bodily fluids including unpasteurised milk <ref>De Lisle, G.W. 1993, Bovine tuberculosis – the New Zealand problem. Proceedings of the New Zealand Grassland Association 55, pp. 199-202. </ref> and by ingestion of the bacteria by consuming or handling an infected carcass, or plant that has been in contact with fluids containing the bacteria. In New Zealand the brushtail possum is the main vector of the M.bovis bacteria and is thought to be a reservoir host <ref>Brown JA, Harris S, White PC, 1994, Persistence of Mycobacterium bovis in cattle, Trends Microbiol, 2(2):43-46.</ref> <ref>Corner LA. 2006, The role of wild animal populations in the epidemiology of tuberculosis in domestic animals: how to assess the risk. Vet Microbiol; 112(2-4):303-312 </ref>. The bacterium affects the possum in a particular way which is unique to other species. The infected possum will search for more food and warm dry shelter, causing them to move onto farm land and residential areas, increasing the potential for transmission to other species. Aerosolization (droplets of infected material suspended in the air) is thought to be the most infectious route of transmission and in some studies accounted for 80-90 percent of infections in cattle <ref>Menzies FD, and Neill SD, 2000, Cattle-to-cattle transmission of bovine tuberculosis. Vet J; 160(2):92-106.</ref>.

Detection

Bovine Tb is very hard to detect as it has a slow reproduction time, this means that it can take years for the disease to fully develop. This means that an infected animal can easily infect others without showing any of the symptoms. Depending on the species that is infected, the progression of the disease is heavily impacted by the host immune system. For example, the disease is known to fully develop in a matter of weeks in cats whereas in cattle it may take years <ref>Thidodeaux, W. 2013, What is Bovine Tuberculosis?, eHow health, Respiratory Disorders Sourced on 7/09/2013 can be found at http://www.ehow.com/about_5032766_bovine-tuberculosis.html </ref>. The most common method for testing for tuberculosis is the tuberculin test (also known as the Mantoux test), where an extract of Mycobacterium tuberculosis (tuberculin) is injected into the animals skin, 48-72 hours later the size of the inflammation is measured and redness or inflammation at this stage is considered a positive indication of tuberculosis <ref>USDA. 2009. Assessment of Pathways for the Introduction and Spread of Mycobacterium bovis in the United States, 2009 USDA–APHIS–VS–CEAH. Fort Collins, CO Avaliable online from http://www.aphis.usda.gov/animal_health/emergingissues/downloads/bovine_tb_pathways_2009030711.pdf. </ref>.

(DoC, 2013c)

Controls

Despite control methods being used in New Zealand since 1893, Bovine TB is still found in most areas of the country <ref>de Lisle, G.W. 1993, Bovine tuberculosis – the New Zealand problem. Proceedings of the New Zealand Grassland Association 55, pp. 199-202 </ref>. Currently in New Zealand there are two main methods used to control bovine tuberculosis. These methods are directed at controlling the animal vectors. As possums are the main vector for the spread of Bovine TB the control of BTB is closely linked to possum numbers. To control possum populations, poisoning and trapping methods are employed with varying degrees of effectiveness. However, choosing which method to employ is controlled by a range of factors, including cost, time, and labour. BTB eradication is defined as 0.2% infected herds <ref>National Possum Control Agencies [NPCA], (undated, but circa 1998), Questions & Answers on 1080 – answers to commonly asked questions on 1080, produced by the National Possum Control Agencies. Department of Conservation, Ministry of Agriculture and Fisheries, Local Government New Zealand, Animal Health Board. Wellington, NZ.</ref>.

The transmission of bovine tuberculosis

Figure 1, Diagram showing contamination cycle

Animals

In the last thirty years, there has been massive government expenditure on controlling populations of tuberculosis vectors, namely brushtailed possums, deer and pigs <ref>Coleman, J.D, and Cooke, M.M. 2001. Mycobacterium bovis infection in wildlife in New Zealand. Tuberculosis 81 (3): 191-202. </ref>. All of these animals have feral populations throughout New Zealand, with the possum presenting the greatest tuberculosis threat to farmed stock in New Zealand. The brushtailed possum has been discovered to be critical in the reinfection of livestock tested free of tuberculosis, as it is the only self-sustaining maintenance host of the bacterium <ref>Coleman, J.D, and Cooke, M.M. 2001. Mycobacterium bovis infection in wildlife in New Zealand. Tuberculosis 81 (3): 191-202. </ref>.

In farmed cattle, tuberculosis is most common in areas infested with tuberculous possums and the highest rates of transfer of the bacteria occur at the pasture-forest boundary <ref>Coleman, J.D. 1988. Distribution, Prevalence and Epidemiology of Bovine Tuberculosis in Brushtail Possums, Trichosurus vulpecula, in the Hohonu Range, New Zealand. Australian Wildlife Research :651-653 pp.</ref>. The bacteria is transferred between possums by inspection of infected feces and urine, as well as agonistic encounters and den sharing <ref>Porphyre, T., McKenzie, J., Stevenson, M.A. 2011> Contact patterns as a risk facto for bovine tuberculosis infection in a free-living adult brushtail possum Trichosurus vulpecula population. Preventative Veterinary Medicine 100: 221-230.</ref>. Deer contract the bacterium via contact with dead or dying possums and are a very transient vector.


Measures for controlling Bovine Tuberculosis

The Timms Trap (NRC, 2013)

1080 and Trapping

Currently in New Zealand two main methods are employed to control bovine tuberculosis, namely through controlling its animal vectors and controlling infected livestock. To control possum populations, poisoning and trapping methods are employed with varying degrees of effectiveness. However, choosing which method to employ is controlled by a range of factors, including cost, time, labour, and possum population density. The poison sodium monofluoroacetate or 1080 is used to control possum numbers, and this poison is aerially dropped over large areas. Trapping and hunting are also employed, and to a far greater extent than aerial poisoning. Aerial methods are used over only 8 per cent of the total treatment area <ref> Environmental Protection Authority. (2011). Aerial Pest Control Operations. Annual Report on the Aerial Use of 1080. 10-15. </ref>. One case study focused on aerial sowing of 1080 and its effectiveness in comparison to ground control methods. The results showed that while both operations achieved a mean percentage kill of 75 percent, 1080 was far cheaper to use than implementing a labour intensive ground based control.

Helicopter doing a 1080 drop over Mount Taranaki (e2nz, 2013)

Aerial sowing of 1080 also covered a far greater area than ground control, with 170-269 hectares covered aerially and 8-13 hectares covered by ground operatives <ref>Montague, T.L. 1997. The relative cost and effectiveness of hunting and aerial 1080 poisoning for reducing possum populations in native forest. Landcare Research Contract Report C9697/82 June 1997. 23 pp.</ref>. While 1080 is currently what is used the most to control the populations of these vectors, other poisons have also been used to control possums in particular. While other potent poisons exist such as cholecalciferol and brodifacoum, these poisons bioaccumulate and can poison other secondary feeders that feed on the remains of those that have succumbed to it <ref>Eason, C.T., and Ogilvie, S. 2009. . A re-evaluation of potential rodenticides for aerial control of rodents. DOC Research and Development Series 312. Department of Conservation, Wellington. 33 pp.</ref>. These other poisons such as pindone, are inhumane on larger animals, whilst being effective on smaller animals. However, in New Zealand the limited finances of the Animal Health Board and Department of Conservation are what dictates the chosen control method, and with 1080 being the cheapest per kilogram this is the poison that is used predominantly <ref>Eason, C.T., and Ogilvie, S. 2009. . A re-evaluation of potential rodenticides for aerial control of rodents. DOC Research and Development Series 312. Department of Conservation, Wellington. 33 pp.</ref>. To sow the poison aerially fixed wing planes and helicopters can both be used, with helicopters costing $5 to $11 a hectare to run, and fixed wing planes only costing $1.90 per hectare <ref>Warburton, B., and Cullen, R. 1995. Cost-effectiveness of different possum control methods. Department of Conservation, Wellington.</ref>.


1080 bait (Stuff, 2011)

However, it is known that as long as any immigration or emigration of tuberculous individuals occurs, then bovine tuberculosis can never be fully eradicated in free or feral populations <ref> Barlow, N.D. 1991. Control of endemic bovine tuberculosis in New Zealand possum populations: results from a simple model. Journal of Applied Ecology 28: 794-809.</ref>. It was noted in much of the literature that possum interactions with one another should be investigated as a perpetuating source of tuberculosis <ref>Porphyre, T., McKenzie, J., Stevenson, M.A. 2011> Contact patterns as a risk facto for bovine tuberculosis infection in a free-living adult brushtail possum Trichosurus vulpecula population. Preventative Veterinary Medicine 100: 221-230.</ref>. One other method that has been investigated, and suggested as the best possible method of control if it worked effectively was sterilization of possums. However, technology and cost prevents this solution from being implemented on a large scale <ref>Barlow, N.D. 1991. Control of endemic bovine tuberculosis in New Zealand possum populations: results from a simple model. Journal of Applied Ecology 28: 794-809.</ref>.


1080 has a history of use in New Zealand and aerial application rates have dropped sharply in the last two decades with improvements in targeting methods. It is a key feature of interest to those in the pest control industry to reduce application rates where possible, and currently the devices used to broadcast the poison from planes and helicopters are designed to sow the poison at a far greater rate than is necessary <ref>Morgan, D.R., Thomas, M.D., Meeken, D., Nelson, P.C. 1997. Less 1080 bait usage in aerial operations to control possums. 50th New Zealand Plant Protection Conference. 391-396 pp.</ref>. To attempt to reduce the amount of poison sown, one particular case study looked at cluster sowing of 1080 to allay concerns over indiscriminate poisoning. A helicopter dropped the poison in clusters and the size of these was determined by the speed of the helicopter and its altitude. It was discovered that these clusters actually were reasonably effective, even with 100 meter spacings between prefeeding areas before the 1080 drop. These clusters are actually hypothesized to draw possums from their core home range to feed as even with sparing amounts of bait the kill percentage was still reasonably high <ref> Nugent, G., and Morriss, G.A. 2013. Delivery of toxic bait in clusters: a modified technique for aerial poisoning of small mammal pests. New Zealand Journal of Ecology 37 (2): 246-255.</ref>.

New Zealand-wide Results from Control Measures

Figure 2 the annual New Zealand expenditure on BTB controls measured against TB infected deer and cattle herds (Christophers, 2013)


Figure 2 displays three factors. The first is the number of cattle herds infected with BTB, from 1977 to an estimate for 2013. An increase which ended in the late 1970s is discernible as BTB erupted following a lessening of the level of BTB control measures of the decade. The advent of deer farming in the late 1960s was not shown until the discovery in the late 1980s of BTB-infected deer herds. Unease from our international trading partners led to the realisation that spending on BTB control measures was inadequate as the number of BTB-infected herds increased sharply through the 1980s.

This was addressed by the formation of the Animal Health Board, an incorporated body, in the 1980s, which was funded initially by levies imposed on cattle farmers (with compensatory provisions). Deer farmers, although also subject to the levy, chose not to avail themselves of the provisions for compensation. Consequently, spending on BTB control underwent a sharp increase from the early 1990s, plateauing in just over a decade as its results led to a decline in the number of infected animal herd (of both cattle and deer).

It remains to be seen whether the current high level of spending (of the order of NZ$50 million p.a.) will remain, or decline as control of BTB has been regained by the end of the first decade of the 21st century.







Indicators

Environmental indicators are formulated using the Pressure-State-Response Model, and these indicators help quantify changes in a system. In New Zealand, the pressure is the presence of BTB carrying vector species in wild populations and their potential to ruin New Zealands agricultural image, the state is the incidence of BTB in farmed stock populations and usually when BTB is located in a population the response that is undertaken by DOC and the AHB is that of slathering the area where the population is located in 1080 poison to control the population. However, it could be considered that human clearing of forested areas for pasture has contributed to BTB infections as infected possums are known to inhabit the forest - pasture ecotone. Indicators also help assess if goals are being met, for example, the AHB have committed to eradicating BTB and keeping BTB infections under 0.4 % of the total population of all farmed stock <ref>Tbfree.org.nz. 2013. TBfree New Zealand. [online] Available at: http://www.tbfree.org.nz/ [Accessed: 3 Oct 2013].</ref>. It could be also considered that instead of 1080 poison sowing being the response to control BTB, trapping until a residual trap catch of 5% or less is achieved could be undertaken.

Key Stakeholders

(TBfreenz, 2013)

TBfree New Zealand

TBfree New Zealand is a subsidiary of OSPRI New Zealand; it is a Non-Governmental Organisation (NGO) which is partially funded by the government and by industry. TBfree's focus is to “manage the implementation of the National Pest Management Plan for Bovine TB (NPMP), with the aim of eradicating the disease from New Zealand” <ref>Tbfree.org.nz. 2013. TBfree New Zealand. [online] Available at: http://www.tbfree.org.nz/ [Accessed: 3 Oct 2013].</ref>. TBfree has three major functions, disease management, movement control and vector operations. TBfree received $2.5 million from the Animal Health Board (AHB) to conduct research in immunology, controlling methods, toxins and epidemiology. TB Free works closely with local people, other agencies, organisation, iwi and conservation organisations, also priding itself on its partnerships with local farming communities. TBfree receives $30 million per year from the government in funding and receive financial support from seven other partners (Dairy NZ, Beef + Lamb NZ, Deer Industry NZ, NZDeer Farmers Association, Federated Farmers NZ, NZ Government, and Local Government New Zealand) <ref>Tbfree.org.nz. 2013. TBfree New Zealand. [online] Available at: http://www.tbfree.org.nz/ [Accessed: 3 Oct 2013].</ref>.

(DoC, 2013a)

Department of Conservation and Animal Health Board

The Department of Conservation (DoC), or Te Papa Atawhai, is the government department responsible for the environment. It is charged with managing New Zealand’s historical and natural heritage through a range of hands on work to promote the growth of native species within national parks, forest reserves and offshore islands<ref>Department of Conservation (2013a) About DoC http://www.doc.govt.nz/about-doc/[Accessed 22/09/13].</ref>. DoC operates with thousands of volunteers every year in order to carry out necessary tasks to ensure that native plants and wildlife have a future in New Zealand. DoC actively works to eradicate the possum species as a form of BTb mitigation, DoC achieves this eradication in two ways: the first is through 1080 poison drops both by aerial and by land, and secondly by trapping which a there is a vast array of traps used <ref>Department of Conservation (2013b) The use of 1080 for pest control – 3.1 Possums as reservoirs of bovine tuberculosis http://www.doc.govt.nz/publications/conservation/threats-and-impacts/animal-pests/the-use-of-1080-for-pest-control/3-why-we-use-1080-for-pest-control/3_1-possums-as-reservoirs-of-bovine-tuberculosis/ [Accessed 23/09/13].</ref>


DoC is closely involved with the Animal Health Board (AHB) which is no part of Tb Free New Zealand. The AHB was largely concerned with mitigating the adverse effects of the spread of bovine tuberculosis (BTB) from wildlife populations to commercial deer and cattle farming. There are several vectors which in AHB focus on, the main one is the possum. The possum is widely known to carry BTb and is one of the main links between wild animal populations and commercial farming populations. In the last 5 years, the Animal Health Board has changed its focus on the BTb problem from targeting the spread of BTb within commercial herds to taking on the spread of BTb in wild animal populations, preventing its spread to farming operations. The roles that both DoC and AHB play in the mitigation of BTb are crucial to New Zealand’s economic and environmental status, because without constant monitoring of the spread of BTB, New Zealand’s dairy and meat exports are under threat <ref>Department of Conservation (2013a) About DoC http://www.doc.govt.nz/about-doc/[Accessed 22/09/13].</ref>.

(Federated Farmers of New Zealand, 2011)

Federated Farmers of New Zealand/ Forest and Bird

(Forest and Bird New Zealand, 2013)

Federated Farmers of New Zealand is an independent collective group of farmers who lobby on behalf of their members. Federated Farmers was first formed in 1945 and was previously known as the New Zealand Farmers’ Union until it merged with the Sheepowners Federation in 1945 (Federated Farmers of New Zealand, 2013). Federated Farmers give voice to regional and national level farmers who seek to encourage sustainability through best practice <ref>Federated Farmers of New Zealand. (2011) About Federated Farmers (Online) available from http://www.fedfarm.org.nz/about-us/ (Accessed 24/09/13).</ref>. One of the key concerns for the Federated Farmers is the spread and control of bovine tuberculosis as they aim to eradicate BTb from commercial farming. At the beginning of 2011, Forest and Bird and the Federated Farmers formed an alliance in which they now work to assist in the eradication and mitigation of Btb. Forest and Bird seek to better inform the public about the effects of BTb and the results of an outbreak of BTb <ref>Forest and Bird (2013) Forest and Bird and Federated Farmers Praise Report on 1080, Retrieved from http://www.forestandbird.org.nz/what-we-do/publications/mediareleases/forest-bird-and-federated-farmers-praise-report-on-1080 [Accessed 26/09/13].</ref>. Both Forest and Bird and the Federated Farmers of New Zealand believe that 1080 is the most cost effective and most reliable form of possum control which will help to control BTb spread.

New Zealand Deerstalkers' Association

(NZDA, 2013)

Formed in 1937, the New Zealand Deerstalkers’ Association (NZDA) is a non-governmental organisation which is New Zealand’s recognised national body generally representing and speaking for hunters <ref>New Zealand Deerstalkers' Association [NZDA](2013) About, Retrieved from: http://www.deerstalkers.org.nz/about/ [Accessed 22/09/13].</ref>. Deer are one species which can carry BTb, although the Deerstalkers' Association is for the mitigation and control of bovine tuberculosis, it is against the use to 1080 as a form of control. 1080 is known to have a high by kill factor and deer are one species which suffers after a 1080 aerial drop. Although deer repellent is sometimes added to 1080 baits, the Deerstalkers’ Association is still very much against the use in areas which recreational hunting is allowed because of the poison which continues to be used. The Deerstalkers Association want to see more reliable tests being formed for BTb because the current tests are only 80 and 90% correct respectively for deer and cattle <ref>New Zealand Deerstalkers' Association [NZDA](2013) About, Retrieved from: http://www.deerstalkers.org.nz/about/ [Accessed 22/09/13].</ref>.

(Ngai Tahu, 2013)

Local Maori, iwi

The vision of the iwi in New Zealand is “Our dream is that our ancestral landscape is protected and our people have living relationships with their whakapapa and traditions through the environment”. Included in this is the preservation of the natural landscape and the native animals within <ref>Ngai tahu, (2013) Te Ao Turoa, Environmental Kaitiakitanga, Retrieved from: http://ngaitahu.iwi.nz/environment/ [Accessed 23/09/13].</ref>. Under section eight of the RMA 1991, it states that the government entities must consult local iwi and “take into account” their wishes if local Maori are considered to be affected parties <ref>New Zealand Legislation Acts (2013), Section Eight, The Treaty of Waitangi [Online] Available from http://www.legislation.govt.nz/act/public/1991/0069/latest/DLM231915.html#DLM231915</ref>. There are several iwi that do not believe in the way in which BTB is being controlled or mitigated, the iwi take particular issue with the aerial 1080 drop with at least three refusing to give consent since 2010 <ref>Mills, L (2011) Coast Iwi says ‘no’ to 1080, Greymouth Star (Online) Retrieved from http://greystar.co.nz/node/136 [Accessed 23/09/13].</ref>.

Case study Akatore area of Coastal Otago, 2002/2003 and 2006.

map showing the section of study area near Akatore in coastal Otago (SPM, 2006)

Detection

As a result of BTB testing performed in a cattle herd in the Akatore area of coastal Otago in 2002, the decision was taken by the Regional Animal Health Control Committee to treat the area as one infected with BTB. This area has a long history of BTB infection and cattle and deer herds in this area are known to have infection rates of more than 25% <ref>Southern Pest Management [SPM](2003) Akatore Operation 2002/2003, (Fact Sheet), Mosgiel, New Zealand.</ref>.

Vector identification

Although cattle were found to be infected, it was quickly ascertained by the discovery of infected possums, that the main vector for infections was diseased possums infected with BTB. Approximately 90% of identified BTB infections are found to result from vectors, mainly possums <ref>Southern Pest Management [SPM](2003) Akatore Operation 2002/2003, (Fact Sheet), Mosgiel, New Zealand.</ref>. This occurred during routine fur trapping operations by private operators. The possum population caught when fur-trapping indicated a residual trap catch (RTC) of approximately 33%. (This means that for every 100 trap nights, a mean number of 33 possums was caught.) The residual trap catch is used as a proxy for gauging population level, but arguably is not indicative nor a reliable indicator of this.

Control measure(s)

More than 100 animals were slaughtered as part of the control measures undertaken to contain this outbreak. Movement control was immediately imposed on livestock, prohibiting the transport of animals from this area without certification for clearance from BTB. Possum population control measures proposed were a combination of ground and aerial operations. Historically this area has proven difficult for possum control because of the variety of tenures, ground cover and physical terrain found there. The area is a mixture of freehold, leasehold and Conservation Public Lands, containing grassland, shrub and forest regrowth, with exotic and indigenous forests. The ground is steep in parts, necessitating that almost half required application by aerial methods, and just over half was able to be treated by ground control methods such as trapping and poisoning <ref>Southern Pest Management [SPM](2006), Akatore Tb Possum Control Operation (Fact sheet), Mosgiel, NZ.TBFree NZ, (2013) Our Role and Function http://www.tbfree.org.nz/our-role-and-function-2.aspx[Accessed, 20/09/13].</ref>.

Timing

Mindful of an earlier operation (performed in the winter of 2003), the dates set for the aerial laying of poison baits is weather dependant, requiring poison drops in June or July. The ground poison operation would take place throughout the winter of 2006 <ref>Southern Pest Management [SPM](2006), Akatore Tb Possum Control Operation (Fact sheet), Mosgiel, NZ.TBFree NZ, (2013) Our Role and Function http://www.tbfree.org.nz/our-role-and-function-2.aspx[Accessed, 20/09/13].</ref>.

Outcome

Control of possum populations are widely accepted as being achieved when an RTC of 5% is realised (DOC AHB, 2003). After the combination of ground and aerial poison operations, this level was attained by October of 2006. Eradication of BTB is considered to be gained by reducing the RTC to below 5% <ref>Southern Pest Management [SPM](2006), Akatore Tb Possum Control Operation (Fact sheet), Mosgiel, NZ.TBFree NZ, (2013) Our Role and Function http://www.tbfree.org.nz/our-role-and-function-2.aspx[Accessed, 20/09/13].</ref>.

References

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