Poison call as rabbit virus loses effect

Farmers need to go back to poisoning rabbits in some areas to reduce populations which have built up resistance to the rabbit haemorrhagic disease illegally smuggled into New Zealand, according to an Otago Regional Council study.

A report on the study to a services committee meeting on Wednesday said previous serum sampling had shown high resistance levels to the virus, with little or no benefits gained from it.

The average level of resistance was 45 per cent, but the latest tests showed that could be turned around.

The study, which involved taking serum samples from several monitor rabbit populations, showed secondary control, such as poisoning, could reduce levels of resistance to the virus which have built up over time.

The latest results indicated that poisoning these problem areas enabled a "resetting" of the rabbit population, the council said.

Debate was now needed on whether landowners should pitch their secondary control at a level to keep rabbit numbers at an acceptable level or try for extermination.

The smuggled virus was deliberately spread by farmers in the South Island's high country, after they smuggled the virus into New Zealand in August 1997.

They were later criticised for using homemade mixtures which risked actually vaccinating rabbits because the mixtures were too weak or damaged by ultraviolet light.

Six years later, average resistance to the virus across the Otago council's monitor sites is 45 per cent, but varies depending on how recently the virus has gone through.

The report noted that flow-on effects to the region of the virus included better vegetative ground cover, greater pastoral production, less damage to horticulture and less use of chemical poison.

Rabbit disease

* Farmers illegally smuggled the virus into NZ in August 1997.

* It was widely spread in the South Island high country.

* Homemade mixtures that were too weak or damaged by UV light may have vaccinated rabbits.

* Resistance rates now average 45 per cent.

- NZPA