Graham Nugent (Landcare Research) says it is amazing there are now less than 80 TB infected deer and cattle herds in New Zealand compared to over 1,700 in 1994. Bovine TB is a bacterial disease that affects not only cattle but humans and many other species, including possums. Because Tb was so widespread in possums in 1994, few people considered it possible to eradicate the disease from New Zealand.
By 2008, however, New Zealand has made huge progress in reducing the levels of bovine tuberculosis (TB) in farmed livestock. That prompted the Animal Health Board (AHB) to propose a new national pest management strategy for TB (NPMS) that aims for local and regional eradication of TB from both livestock and possums (the main wildlife host) by 2026. This goal is endorsed by farmers and industry and local who want to protect our reputation as a supplier of safe, high quality meat and dairy products. In late 2010, the proposal for the new NPMS was accepted by the government.
Landcare Research’s work for the AHB contributed substantially to the success of the previous current NPMS, which is on track to achieve fewer than two in a thousand herds (0.2%) infected by 2013. The emphasis now is on local eradication of TB from wildlife – decreasing the cost of reducing possums to very low density while also reducing the amount of poison used, developing alternative methods for breaking the TB cycle, and developing new tools for quickly showing TB has been eradicated locally, so that possum control can be stopped.
Significant projects are being conducted in two remote high country stations, the last areas in northern Canterbury where TB levels in cattle and wildlife had been high. A large-scale aerial poisoning operation in 2008 piloted two new approaches – targeting high-possum-density areas predicted to have the highest risk of TB-infected animals, and a new low-cost, low-toxin approach to 1080 poisoning. This trial completed the implementation of possum control over the most critical parts of the infected area. By 2010 (and for the first time in a more than two decades) the number of TB suspected found by skin testing live animals had dropped to almost zero. In addition pigs, which are highly susceptible to infection when TB-infected possums are present, have been deliberately released in the area as sentinels for detecting TB. Few of the sentinel pigs inside the managed areas have become infected, compared with most of those in an unmanaged area. There is still some infection in both cattle and pigs, but the hope is that the rapid downward trend in the level of infection will continue.
An additional management approach, which is being developed in collaboration with AgResearch and Otago Innovation, a vaccine (BCG) used to protect humans from TB is also showing promise in protecting free-ranging cattle form the natural sources of TB in this area. Partway through the trial, only one (0.6%) of 160 vaccinated cattle have had visible TB infection when slaughtered compare to 10 (5.2%) of 193 vaccinated cattle. Vaccination of cattle may therefore be useful as an interim tool for reducing TB in livestock in areas where it is impractical to undertake effective control of possums.