New virulent strains of rabbit haemorrhagic disease (RHD) are being developed but they are a long way from becoming a realistic control tool for Otago farmers, the Otago Regional Council says.
Landowners across Otago are battling increased RHD immunity among rabbit populations and the possibility of an early breeding season this year.
New data from an Otago Regional Council sampling programme in February and March showed immunity levels among rabbits in Otago is at 73 per cent compared with 68 per cent in 2011 and 69 per cent in 2009.
In a first for the programme, which has been running since RHD was released in 1997, all 30 rabbits tested at a site near Dunback were immune.
It also indicated next season's rabbit-breeding season could start early as the rabbits are in very good condition and could retain enough condition to start breeding early.
Council regional services director Jeff Donaldson said at a regulatory committee meeting yesterday researchers in Australia and New Zealand were investigating strains of RHD that were more virulent than those already here.
In Australia, researchers had identified three strains which could kill resistant rabbits.
By the end of this year, the researchers hoped to identify which strains offered the best potential. Pending the approval process, these strains could be released and monitored in Australia by 2015.
However, at this stage, there was no information the new strains, which were a small mutation of the original virus, would work, he said.
The information gathered in the sampling programme would be "invaluable" should new strains of RHD be released into Otago, he said.
Mr Donaldson did not believe any farmers would be "silly" enough to repeat the uncontrolled release of RHD, as they were more aware of the risks of immunity and to biosecurity.
Cr David Shepherd said while a new strain "potentially" could help control rabbits, it was not time for farmers to "take the foot off the accelerator" on secondary control work.
Mr Donaldson said the benefits of RHD on large areas of highly rabbit-prone land in Central Otago had "decreased markedly" over the years. As a result, greater control was needed by a range of methods such as shooting, fumigation and poisoning, alongside RHD.
The virus provided the greatest benefit on properties with low to moderate rabbit levels.
The committee approved the continuation of the RHD sampling programme, which was done every two years.