History of TB control in New Zealand

In New Zealand, we embarked on 'test and slaughter' measures for TB during the mid-to-late 20th century. By 1970 all cattle herds were undergoing:

• regular TB testing or post-mortem inspection for TB
• compulsory slaughter of suspected TB cases that tested positive
  partial quarantine of infected herds.

The 'test and slaughter' approach

By the 1980s, we had eradicated TB from cattle populations across large areas of the country. This included Northland, Taranaki and mid-Canterbury. However, this was not the case in other regions, like:

• the central North Island
• the Wairarapa
• the West Coast.

In these areas, the test and slaughter approach failed. This suggested something else was infecting livestock.

Possums: the missing link

In 1969, vets found proof that the invasive brush-tail possum was carrying bovine TB — and passing it to farmed cattle and deer. But we don't know how long possums have been carrying TB. Evidence shows that the disease crossed between cattle and possums in as few as 20 separate incidents across the country. 

Possums were the perfect host for TB. They had no evolutionary exposure or resistance to the disease. And, with abundant food and no natural predators, the population in NZ 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 the central North Island.

Public funding withdrawn

The government started investing in possum control for forest conservation purposes in the 1970s. Resources were allocated to areas with major TB problems. This led to a sharp decline in livestock infection levels throughout the late 1970s.

But, in 1978 government funding for possum control was withdrawn due to:

• complacency
• government austerity
• a spike in fur prices which led to the belief that fur hunters would control the problem at little cost to the public.

A fragmented approach

The problem of inadequate funding was made worse by an ad hoc and fragmented approach to TB control in general.

The Ministry of Agriculture ran a livestock 'test and slaughter' programme, funded by industry levies. This proved futile against a growing wave of TB infection by possums. Possum control was left to a network of locally funded pest destruction boards, though they had some support from the national Agricultural Pest Destruction Council (APDC).  

The APDC was constrained by inadequate local funding and conflicting pest management priorities. In 1989, both the APDC and local pest boards were dissolved in a major reform of local authorities. New regional councils inherited their staff, infrastructure and functions, despite having no clear or legislated responsibilities for pest management.

Infected herd numbers peak

We saw a gradual and then exponential increase in TB in livestock during the 1980s. This peaked in 1994, with over 1700 cattle and deer herds infected with TB. This represented a herd infection prevalence of more than 2%, far higher than in most other developed countries. It created a potential risk to our New Zealand beef, dairy and venison export industries.

The Animal Health Board

During the 1980s, the government delegated national TB control policy and decision-making to an industry-led advisory committee. The committee became an incorporated society — the Animal Health Board (AHB) — in 1993. Its mission statement was 'to eradicate bovine tuberculosis from New Zealand'. Membership of the AHB came from:

• Federated Farmers
• dairy, beef and deer industry groups
• local government.

The first national TB strategy

Working through the Biosecurity Act of 1993, the AHB proposed a National Pest Management Strategy (NPMS) for bovine TB. This came into effect in 1998.

The AHB assumed management and legal control of the TB programme and operations under the Biosecurity Act, and:

• gained access to funding through a levy on cattle slaughter
• negotiated for further funding from the Crown, industry organisations and local government.

It also formalised relationships with:

• the state-owned enterprise AgriQuality NZ, for veterinary services, livestock TB testing and movement control
• regional councils, for management of wildlife TB vector control (possum control).

TB continues to spread

Based on historical experience and funding expectations, NPMS’ initial objectives were to:

• curb and reduce the level of TB in livestock
• prevent further geographic spread of TB in wildlife, in what were known as Vector Risk Areas (VRAs). 

The number of infected herds fell to 666 by June 2000. But, we saw more TB infection in wildlife, particularly:

• east of Lake Taupō into the Hawke’s Bay region
• through Kahurangi National Park into the Tasman District
• southward from north Canterbury.

A new strategy

In 2001, recognition of this problem led to funding increases for TB control, from both the government and industry.

These increases foreshadowed a major review of the NPMS. AHB proposed the review in 2001, and it was completed through a strategy amendment in 2004.

The amendment introduced what was then considered a challenging goal. This was 'to reduce the national herd infection rate to no more than 0.2% by 2013'. Achieving this goal would mean New Zealand met the international standard for 'official freedom' from TB in cattle and deer herds.

The technological and managerial improvements in TB control were what led us to believe we could achieve this goal.

Technological advances

The introduction of the Residual Trap Catch Index (RTCI) gave us a reliable and affordable way to:

• estimate possum populations
• measure the effectiveness of our control operations.

It also provided the basis for performance-based, commercially contracted possum control. Within a few years, possum control shifted from being a local government service into a commercial activity.

Further research led to improvements in the cost-effectiveness and reliability of possum control. This included:

• the development of encapsulated cyanide possum bait
• greater precision in aerial 1080 baiting operations, supported by GPS technology.

The commercial model

The AHB inherited a state monopoly in the area of TB control, which it broke by developing in-house management systems. This meant field operations could be offered for commercial tender across the regions. As a result, the private veterinary sector started competing for this work.

Other technical and managerial improvements included:

• more accurate diagnostic TB testing of livestock
• tighter controls on movement of stock from infected herds
• compulsory ear-tagging of cattle and deer to identify their herd of origin — leading to more reliable tracing of infection sources.

Progress towards targets

Progress towards the 0.2% infected herd prevalence target soon exceeded expectations. This was due to:

• regular possum control in more areas
• better than expected performance in possum control operations.

The geographic spread of infected wildlife populations was also curbed, and we eradicated TB from wildlife in some areas. By June 2007 we had:

• 148 infected cattle and deer herds
• a herd infection prevalence rate of 0.39%.

This led to a re-think of the feasibility of total eradication of TB from both herds and wildlife. Eradication is the obvious and ideal end point for any disease management programme, but we had always considered eradication too difficult to be realistic.

We had achieved eradication of TB from wildlife in places like Kaipara South Head and Banks Peninsula. Could we achieve it in much larger areas of heavily forested, rugged possum habitats too?

Improved performance in large scale aerial-baiting operations for possum control emerged as the possible answer to this question. In 2004 and 2005, aerial control operations were completed in:

• the Hokonui Hills in Southland
• the Hauhungaroa Ranges west of Lake Taupo.

This reduced possum density to about 1 animal per 100 hectares, over areas of up to 50,000 hectares. If we could maintain these low numbers, we could expect to eradicate the disease.

A new roadmap for eradication

In late 2007, the AHB proposed a range of options for future control and eradication of TB in New Zealand. This happened in the lead-up to a 5-year review of the NPMS, due by 2009. AHB member organisations and the government 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 objectives for 2011 to 2026 were:

• to eradicate bovine TB from all species in 2.5 million hectares (25% of the total area occupied by infected wildlife) — including 2 large, forested areas representing difficult environments
• to prevent TB from becoming established in wildlife in any area currently free of TB
• to maintain infected herd numbers at no more than 0.4% during the term of the strategy.

Between 2011 and 2016, we:

• achieved eradication of TB from 1.6 million hectares
• got proof that eradication is feasible in challenging areas, like the Hokonui Hills
• maintained an annual infected herd rate well below the 0.4% target (at 0.09%) with 43 infected herds in 2016.

This work laid the foundations for the next phase of the eradication programme.

The TB plan — making eradication a reality

Under the Biosecurity Act, a review of the national TB plan needed to be done by 1 July 2016. As part of this, the government and industry partners had to define and agree on a sustainable funding arrangement. The review began in 2015 by consulting with farmers, local communities, and other stakeholders on the proposed changes.

The new TB plan was approved by government in June 2016. It gives us a nationally coordinated and long-term approach to eradicating TB from New Zealand.

The key objectives of the plan are to achieve:

• TB freedom in livestock by 2026
• 'statistical freedom' (high confidence the disease is gone) in possums by 2040
• biological eradication of TB from New Zealand by 2055.