Twenty cases of an unwanted rabbit virus have been found in Otago.
A report to the Otago Regional Council this week details the effectiveness of the RHDV 1 ''K5'' virus which the council released last March to cull wild rabbits in the region.
It also says there have been 20 positive results from across Otago of the unwanted RHDV 2 virus, and more suspected cases are being tested.
The first case was confirmed by the council last month.
This created a concern among some councillors that rabbits would develop immunity to the council-released virus.
The report said the council was unsure what effect RHDV 2 would have on the effect of both the strains of RHDV 1 virus.
The first rabbit infected by RHDV 2 was found in Marlborough in May and cases were later confirmed in the Bay of Plenty, Nelson, Waikato and Wellington.
The council did not answer questions yesterday regarding whether there was concern about the virus, or where it was found within the region.
The report outlines the effectiveness of the council virus, saying the rabbit population decreased by 47% in selected areas since its release.
This exceeded the 30% to 40% reduction predicted by Landcare, it said.
However, some areas had no change, which the council attributed to high background immunity levels in some areas.
An example was Lowburn, Central Otago, where there was no detectable reduction.
Regarding what effect RHDV 2 has had, scientists had to look to Australia, Cr Graeme Bell said.
''It's been there for some time. You look over the fence and see what your neighbour has done.''
Some farmers were ''very concerned'' about rabbit numbers, with reports of a ''huge outbreak'' recently in Queenstown.
In a release last week, Cr Michael Laws said central and local government needed to admit the virus had not worked.
The claim the virus had an effect lacked ''scientific data or rigour'', he said.
