Research affirms Tb strategy

Targeting possums to stop the spread of bovine tuberculosis is the right thing to do, new research has shown.

Landcare Researchers have confirmed that ferrets and pigs have little or no role in spreading the disease, but were end hosts.

Ivor Yockney, from Lincoln, told the recent Federated Farmers High Country committee conference that research on Molesworth Station tried to determine the roles of pigs and ferrets in spreading the disease.

It confirmed they were the end hosts and that possums remained the main culprit.

Mr Yockney said the research looked at the relationship between habitat, altitude, wildlife and possum numbers, the seasonal movement of ferrets and possums, the prevalence of Tb in pigs, ferrets and possums, the status of pigs in spreading the disease and identifying priority areas for vector control.

Possums were caught over all terrain, from valley floors to scree slopes 1700m above sea level, but numbers did decline the higher the altitude.

The movement of pigs and ferrets during vector control programmes was considered a risk in negating poison efforts in specific regions.

Mr Yockney said as part of the research, pigs and ferrets were caught and had radio tracking gear attached.

This showed pigs operated in a home range of 7ha and ferrets 236ha, with no obvious changes in their range between seasons, leading to the conclusion they would not compromise regional operations.

"Movement of species is unlikely to compromise partial Tb vector control operations," he said.

Further research looked at the prevalence of Tb in the three species.

Ferrets in non-controlled areas had a Tb infection rate of 23% and in controlled areas 16.5%, which showed there was little evidence that targeting the species would reduce infection.

Pigs were sensitive to Tb and were considered a strong indicator that Tb was present in wildlife.

Mr Yockney said pigs aged between 6 months and 2 years were extremely susceptible to contracting Tb and in the trial 100 pigs were killed, with 85% infected.

An aerial poison operation dramatically reduced the pig population and infection, but further research showed there was little, if any, pig-to-pig infection.

In two trials, each over four to eight months, 33 pigs were enclosed in 1ha pens, a mix of infected and clean pigs.

In addition, several clean pigs were released on to Molesworth and monitored.

In two years, just one clean pig in the enclosure contracted Tb but 83% of the clean pigs released on to the station were confirmed as having the disease.

"Pig-to-pig transmission accounts for very little of the high level Tb in Molesworth pigs. You need another species to spread Tb," he said.

The research confirmed that possum control was the most effective in combating Tb and the research also identified the best terrain on which to successfully target the largest number of possums.