Like most developed nations, New Zealand progressively embarked on "test and slaughter" measures during the mid-to-late 20th century. By 1970 all cattle herds were undergoing regular TB testing or post-mortem inspection for the disease, along with compulsory slaughter of test-positive suspect TB cases and partial quarantine of infected herds.
By the 1980s, TB had effectively been eradicated from cattle populations across large areas of the country such as Northland, Taranaki, and mid-Canterbury. This was not the case in other regions, such as the central North Island, the Wairarapa and the West Coast. In these areas, the test and slaughter approach was failing, suggesting that it was something else maintaining the disease and reinfecting livestock.
In 1971, veterinarians found concrete proof to support their long-held suspicion that the invasive brush-tail possum was carrying bovine TB and passing it back to farmed cattle and deer. We still do not know how long possums have been carrying TB, but the evidence shows that TB crossed the species barrier between cattle and possums, in possibly as few as 20 separate incidents across the country.
Possums were the perfect TB maintenance host and vector. They had no evolutionary exposure or resistance to the disease, and with abundant food and no natural predators, their population density in New Zealand was far higher than in their native Australia. By the 1970s, possum-related TB was a major cause of livestock infection in heavily forested areas like the West Coast, Wairarapa and central North Island.
The Government had been investing in possum control for forest conservation purposes for some time. These resources were largely reallocated to areas with major TB problems, leading to sharp declines in livestock infection levels through the late 1970s. But in 1978, taxpayer possum control funding was mostly withdrawn due to complacency, public austerity and a spike in fur prices which led to the belief that fur hunters would control the problem at little cost to the public.
The problems of inadequate possum control funding were compounded during this period by an ad hoc and fragmentary approach to TB control in general. The Ministry of Agriculture continued with a livestock test and slaughter programme, increasingly funded by industry levies, but this was proving futile against a growing wave of possum-vectored infection. Possum control was mostly left to a loose network of locally funded pest destruction boards, with some support and guidance from a national Agricultural Pest Destruction Council (APDC).
While APDC trained a cohort of skilled managers and officers, its efforts were constrained by inadequate local funding and conflicting pest management priorities. APDC and local pest boards were eventually dissolved in a major reform of local authorities in 1989. The newly created Regional Councils inherited their staff, infrastructure and functions, despite having no clear or legislated responsibilities for pest management.
The result was a gradual and then exponential increase in TB in livestock through the 1980s, peaking with over 1700 infected cattle and deer herds in 1994. This represented a herd infection prevalence of more than 2% – far higher than in most other developed countries, creating a potential risk to the marketability of New Zealand beef, dairy and venison exports.
During the 1980s, the Government gradually delegated national TB control policy and decision-making to an industry-led advisory committee. This committee was formalised as an incorporated society – the Animal Health Board (AHB) - in 1994. Its mission statement was ‘to eradicate bovine tuberculosis from New Zealand’. Its membership was drawn from Federated Farmers, dairy, beef and deer industry groups and local government.
Working through the Biosecurity Act of 1993, the AHB proposed a first National Pest Management Strategy (NPMS) for bovine tuberculosis, which came into legal effect in 1998. As a management agency under the Biosecurity Act, the AHB assumed management and legal control of the TB programme and operations. It also gained access to funding through a levy on the slaughter of cattle and was able to negotiate for further funding from the Crown, industry organisations and local government. Contractual relationships were formalised with the state-owned enterprise AgriQuality NZ for veterinary services, livestock TB testing and movement control, and with regional councils for management of wildlife TB vector control (mostly possum control).
Based on historical experience and funding expectations, the initial NPMS objectives were to curb and slightly reduce livestock TB prevalence levels, and to prevent the further geographic expansion of TB in wildlife, in what were termed Vector Risk Areas (VRAs). The former objectives were achieved, with the number of infected herds falling to 666 by June 2000. However, vector control resources were insufficient to prevent further expansion of wildlife infection, particularly from east of Lake Taupo into the Hawke’s Bay region, through Kahurangi National Park into the Tasman District, and southward from north Canterbury.
Recognition of this problem led to substantial funding increases for TB control, from both the Crown and industry, from 2001. These increases foreshadowed a major review of the NPMS, which was proposed by AHB in 2001 and completed through a strategy amendment in 2004. The 2004 NPMS amendment introduced what was then considered to be an extremely challenging objective: ‘to reduce the national herd infection rate to no more than 0.2% by 2013’. This would allow New Zealand to meet the international standard for ‘official freedom’ from TB in cattle and deer herds. Belief that this ambitious objective could be achieved was founded on major technical and managerial improvements which had been introduced after 1998.
Perhaps the most important advance was the introduction of a reliable and affordable standard method for estimating possum population density – the Residual Trap Catch Index (RTCI). This improved decision-making and provided a tool for measuring the effectiveness of control operations. It also provided the basis for performance-based, commercially contracted possum control. Within just a few years, possum control shifted from being a local government service into a commercial activity, driven by profit, efficiency and innovation. Technical advances arising from research resulted in improvements in the cost-effectiveness and reliability of possum control. Major technical gains included the development of encapsulated cyanide possum bait and greater precision in aerial 1080 baiting operations, supported by GPS technology.
Commercial drivers were also introduced to livestock TB testing and management. The AHB had inherited a state monopoly in this area, which it broke by developing in-house management systems. This enabled field activity to be regionalised and offered for commercial tender. As a result, the private veterinary sector became able to compete with the SOE, resulting in a sharpening of performance by both.
Other technical and managerial improvements included more accurate diagnostic TB testing of livestock, tighter controls on movement of stock from infected herds and compulsory ear-tagging of cattle and deer to identify their herd of origin, leading to more reliable tracing of infection sources.
Progress towards the 0.2% infected herd prevalence target soon exceeded expectations. This was largely due to more areas being under regular possum control and better than expected performance in possum control operations. The geographic spread of infected wildlife populations was also curbed, and eradication of disease from wildlife was achieved in some areas. By June 2007 there were 148 infected cattle and deer herds in New Zealand, with a herd infection prevalence rate of 0.39%.
These positive results led to a re-think of the feasibility of total eradication of the disease from both herds and wildlife. Eradication is the obvious and ideal end point for any disease management programme, but the problems and extent of wildlife infection in New Zealand had been considered too difficult for eradication to be realistic. Eradication of TB from wildlife had been achieved from sites such as Kaipara South Head and Banks Peninsula, but could it be achieved across much larger areas of heavily forested, rugged possum habitats?
Greatly improved performance in large scale aerial baiting operations for possum control was emerging as the possible answer to this question. In 2004 and 2005, aerial control operations in the Hokonui Hills in Southland and the Hauhungaroa Ranges west of Lake Taupo had reduced possum densities to about one animal per 100 hectares over areas up to 50,000 hectares. If these low densities could be maintained, without any surviving patches of possums, and with effective measures to prevent immigration of infected wildlife, then eradication of the disease could be expected as the last infected possums died without infecting other animals.
Theoretical modelling supported these assumptions, leading to the development of detailed disease eradication strategies. In late 2007, the AHB floated a range of options for future control and eradication of TB in New Zealand, in the lead-up to a five-year review of the NPMS due by 2009. AHB Member organisations and the Crown then agreed to put forward a preferred option to amend the NPMS to provide for operational and strategic proof of the eradication concept. The formal strategy review and amendment process was completed by mid-2011.
The agreed NPMS objectives from 2011-2026 were to:
OSPRI, with its industry partners, has made excellent progress to meet the goals of the TB Plan since 2011.
This work laid the foundations for the next phase of New Zealand’s TBfree eradication programme.
Under the Biosecurity Act, a review of the national TB plan was required to be completed by 1 July 2016. This included defining a sustainable funding arrangement that would be agreed between the Government and industry partners. The review began in 2015 and was overseen by the Plan Governance Group (PGG), comprising representatives of funding organisations, OSPRI, and wider stakeholder interests.
Consultation on the proposed changes to the TB Plan was conducted with farmers, local communities, and other stakeholders in June and July 2015. The new TB Plan was formally approved by the Government in June 2016. The result of this process is a plan endorsed by farmers, industry and central Government that provides a nationally coordinated and long-term approach to manage and eventually eradicate TB from New Zealand.
The key objectives of the TB Plan are the biological eradication of TB from New Zealand by 2055, with TB freedom in livestock by 2026 and "statistical freedom" in possums (in other words, high confidence the disease is gone) by 2040.
An important aspect of the plan has been the introduction of more targeted approaches to TB testing and pest control. A major focus for OSPRI has been ensuring key stakeholders understand the implications of the new funding model, the key policies of the new plan and importantly the timeline for change.