Possums are the main cause of bovine tuberculosis spreading between herds of cattle and deer, according to Operational Solutions for Primary Industries (OSPRI) which manages the $80 million per year TBfree programme on behalf of New Zealand farmers and the public.
OSPRI group manager new business Peter Alsop told the Otago Daily Times yesterday Tb infection in possums ''causes about 70% of herd infections''.
The remaining infections, he said, were caused by movement of cattle or deer with undetected Tb, but those infections were also likely to have initially been generated by infected wildlife.
Mr Alsop was responding to a suggestion from New Zealand First MP Richard Prosser the Tb problem in possums had been overstated and aerial drops of 1080 poison, targeting possums, were not needed.
Two such drops are planned for the Wanaka area this month.
Mr Prosser noted none of the 9838 possums autopsied in New Zealand last year had Tb, and only 54 possums from 124,213 autopsied over nine years had the disease.
However, Mr Alsop pointed out autopsies were only carried out in certain areas.
''Where we know Tb exists in wildlife, our focus is on controlling the disease through possum control, and not on spending money unnecessarily capturing and examining possums for signs of disease.
''In other areas, where the programme is getting close to eradicating the disease, the emphasis switches to surveillance work to carefully prove that the disease no longer exists - a process that does require individual possum capture and examination.
''Overall, finding fewer and fewer infected possums, and fewer and fewer infected herds, is a positive sign the programme is working.''
Mr Alsop said the TBfree programme had resulted in a reduction of infected cattle and deer herds from about 1700 in the late 1990s to the present level of fewer than 50 herds.
And about a million hectares of New Zealand was free of the disease, Mr Alsop said.
''The programme is running effectively and ahead of predictions.
''Unless Tb is eradicated from the possum population, Tb infections in cattle and deer can return.''
Tb in cattle and deer herds caused production loss and ''a wide range of other adverse consequences for farmers'', Mr Alsop said.
The TBfree programme is being reviewed, and public workshops are planned for Winton, Mossburn and Cromwell on July 6 and Gore, Balclutha and Mosgiel on July 7.
Bovine Tb facts
Bovine tuberculosis in Otago
• Otago had six infected herds on June 1.
• In 2006 there were 37.
• In the mid 1990s there were more than 300.
• Otago has 2 million ha where the disease still exists in wild animals.
• Between July 14 last year and June 1 this year, 530,000 cattle and deer underwent Tb testing in Otago.
Source: OSPRI.
