Rabbit Disease (Calicivirus) to be released
26 May 2005
Rabbit Haemorrhagic Disease (Calicivirus) to be released
A consortium of ten regional councils, including the Auckland Regional Council, has gained approval from the Environmental Risk Management Authority (ERMA) to import batches of the Rabbit Haemorrhagic Disease (RHD) virus strain from the New South Wales Department of Agriculture.
RHD, formerly known as Rabbit Calicivirus Disease, is a naturally occurring virus found in wild rabbits in Asia and Europe.
The council consortium has developed a protocol for RHD release to ensure safe storage. Only specific regional council staff and licensed operators are involved.
The most rabbit-prone parts of the region will be targeted during July, and include Pukekohe, Karaka, Awhitu, Omaha, Great Barrier Island and Shakespear Regional Park.
ARC Chairman Michael Lee said: "Rabbits are a serious problem on farmland, coastal areas and in market gardens. They eat pasture, rare coastal native plants and vegetables, and can have a major effect on regenerating bush, shelter belts and orchards, where they ringbark trees and eat seedlings.
"Rabbits also cause erosion, particularly on coastal sites such as Awhitu, Omaha, and Great Barrier Island."
ARC Biosecurity Manager Jack Craw says Auckland Regional Council will publicise the proposed releases beforehand, and advise of the need for vaccination, though most pet rabbits in the region are already inoculated.
"RHD is a humane control compared with alternative control methods," he says.
"We will also consider other sites for release.
"RHD will not eradicate rabbits but will reduce populations to a more sustainable level, so that further control by other methods is more feasible. For example, where RHD has brought populations down to low numbers, night shooting or baiting should be used to clean up remaining rabbits," Mr Craw says.
Rabbits were introduced into New Zealand in the late 18th to mid-19th century, initially to offshore islands as a food source for shipwrecked sailors, and subsequently on to the mainland to establish a fur industry and for hunting. By the 1890s they had become a pest throughout most of New Zealand.
A number of rabbit control methods have been developed, ranging from poisons and shooting, erection of rabbit exclusion fences and use of ferrets. Most have limited effectiveness, as they only affect rabbits in a limited area, are costly, require much labour and often don't work very well.
RHD was illegally introduced into New Zealand in 1997 from Australia and was spread widely by farmers throughout the country. It is now common in the Auckland region, with the possible exception of Great Barrier Island.
The Ministry of Agriculture & Forestry conducted research on native and exotic species and confirmed no effects on other species whatsoever. RHD was legalised in 1998, which allowed regional councils and other bodies to spread the disease over all of mainland New Zealand. Very significant rabbit control was obtained. For example, in Central Otago, prior to RHD, 3000 to 5000 tonnes of carrot bait were used each year in wide-scale rabbit poisoning operations. Since 1997 only a few dozen tonne has been used each year.
RHD-infected rabbits rapidly weaken, and normally seek cover so few carcases are apparent. The disease is naturally spread by rabbit-to-rabbit contact, vapour and over longer distances by flies.
Almost all adult rabbits newly exposed to RHD will die, however infection does pass on conferred immunity to suckling kittens. These rabbits will remain immune to RHD for life, but immune rabbits do not pass this immunity on. Immunity also develops after exposure to poorly handled virus. Immunity levels quickly rose after the initial illegal release, due in part to sloppy virus storage and poorly timed application.
The disease has sporadically flared up within the Auckland region in the last two years. The farming sector (and also some Beachcare and Landcare groups) has called for further controlled releases of the virus.
A very effective vaccine against RHD, called Cylap, is commercially available and many pet rabbit owners and commercial breeders inoculate their rabbits. The vaccine is a once-only treatment and extremely cheap. Rabbits with the virus, whether immune or non-immune, are safe to eat. In fact a large percentage of the rabbits consumed since 1997 would have been exposed to RHD.
Rabbits breeding is low or nil in cold weather so releases will only be made at the coldest part of mid-winter to minimise or prevent onset of immunity.