Waikato Regional Council is urging residents to report any sightings of wild rabbit carcasses in areas where the RHDV1 K5 virus was released in April.
At the same time, landowners are being urged to continue with their rabbit control operations over winter.
The virus was released in Taupō, Kinloch, Omori/Kuratau and Whakarawa, as well as Matarangi, Pauanui, Whangamatā, Thames, Hamilton and Cambridge/Karāpiro.
“To be able to assess the effectiveness of the K5 release we are keen to hear of any sightings of wild rabbit carcasses so they can be collected for testing,” said council biosecurity pest animals team leader, Brett Bailey.
“To date we have had only a couple of reports – one in Karāpiro and another in Taupō – and there could be a number of reasons for this. Rabbit densities dropped significantly throughout the region, particularly in Kinloch, prior to the K5 release. We think this could be due in part to a spike in the pre-existing virus.
“The particularly cold temperatures experienced around the time of the virus release could also have prevented the virus from spreading as hoped. Flies, in particular, play an important part in helping the virus to spread and of course they drop off when the temperature dips,” he said.
“This virus was never going to be a silver bullet for rabbit control, which is why more traditional control methods need to be maintained.”
Mr Bailey said testing of rabbit carcasses would also help the council identify if the newly discovered European rabbit calcivirus, known as RHDV2, is in the Waikato.
RHDV2 was recently confirmed in the Bay of Plenty after testing of two wild rabbits found on a Rotoehu farm.
RHDV2 affects European rabbits and at least two species of hares (Sardinian Cape hare and the Italian hare) and can cause mortality in young animals from 11 days onwards.
Vaccines for the viruses have been imported into New Zealand and are available through veterinarians for pet rabbits.