RHDV1 K5 in Victoria
Rabbits are Australia's most destructive agricultural pest animal, costing $200 million in lost agricultural production every year, with a further $6 million expended on rabbit control measures.
Rabbits also impact the environment. Less than one rabbit per hectare is enough to stop the growth and regeneration of some native species and negatively affect biodiversity. The threat abatement plan released by the Australian Government Department of the Environment in 2016 found that rabbits are a significant threat to biodiversity, affecting 304 nationally threatened plant and animal species.
RHD Boost is a 20 year national biological control project that involved the release of a naturally occurring Korean variant of rabbit calicivirus called Rabbit Haemorrhagic Disease Virus K5 (RHDV1 K5).
This was a national project to introduce a new variant of RHDV1 into Australia, to improve the control of rabbits, particularly in areas where calicivirus has had limited impact on rabbit populations.
What is RHDV1 K5?
RHDV1 K5 is a variant of Rabbit Haemorrhagic Disease Virus (RHDV1) or calicivirus that causes a fatal haemorrhagic disease in the European rabbit (Oryctolagus cuniculus). It was released in March 2017 to improve rabbit biocontrol in Australia, as part of the RHD Boost program. RHDV1 K5 is not a new virus. It is a Korean variant of the original Czech strain of RHDV1 that was released in 1996.
RHDV1 K5 was selected over 37 other potential variants because it was able to overcome a benign form of the virus, RCV-A1, that was providing rabbits in cooler/wetter regions with a level of protection from the original Czech strain. RHDV1 K5 was also able infect those that had begun to develop a level of resistance to the original Czech strain, since it had now been present in the Australian landscape for nearly 20 years.
The national release of RHDV1 K5 occurred at 323 community release sites and 18 intensively monitored sites, but not before it was rigorously tested, assessed and registered as part of a strategic collaboration between research providers, government and industry bodies. Upon its release, RHDV1 K5 was able to produce an average rabbit population knockdown of 34%, although it’s important to note that the results were highly variable. It was also discovered that RHDV1 K5 worked more as a biocide, rather than a biocontrol agent; meaning it generally did not spread beyond the original release site like a self-disseminating biocontrol agent would.
Consequently, farmers and other land managers should continue to use an integrated and coordinated approach to manage rabbits, which include a well-designed warren ripping component that is complemented by other control techniques.
Where does RHDV1 K5 work
RHDV1 K5 works in a range of different habitats though it was selected for its ability to overcome a benign form of the virus (RCV-A1) that was providing rabbits in wetter cooler regions with protection from the original Czech strain of the virus, that was released in 1996. Importantly, RHDV1 K5 could also control rabbits that had started to develop a resistance to the original Czech strain.
Safety of RHDV1 K5
No variant of RHDV1 (K5 or the Czech strain) has ever been found to cause infection in any other animal except the European rabbit (Oryctolagus cuniculus). Pet rabbits are also affected by both RHDV1 strains, as they are descendants of wild rabbits. Even predatory animals that eat a rabbit which has died from RHDV1 K5 do not develop an infection. RHDV1 (K5 and the Czech strain) are safe for people, pets, wildlife and livestock.
RHDV K5 is more humane
RHDV1 K5 is one of the more humane methods of controlling wild rabbits. The rabbits develop 'cold-like' symptoms, become lethargic and then quickly die.
Post-infection, there is a rise in body temperature lasting up to 24 hours, followed by, in 70 to 90% of cases, death within 48 hours after the onset of a fever. The overall welfare impact prior to death has been assessed as low using the relative humaneness model developed under the Australian Animal Welfare Strategy.
Owners of pet rabbits are advised to vaccinate their animals against the virus.
There is a vaccine (Cylap®) for prevention of RHDV1 K5 and the Czech strain of RHDV1. This vaccine has been shown to be effective against RHDV1 K5 and the Czech strain of RHDV1 provided that the correct vaccination protocols are followed. Talk to your vet for further information on vaccinating pet rabbits against RHDV1 K5 virus and other measures to prevent disease.
When to vaccinate
The Australian Veterinary Association recommends vaccinating rabbits against RHDV1 at 10 to 12 weeks of age and then give an annual booster and health check. Occasionally in the face of an outbreak rabbits may be vaccinated earlier than 10 weeks of age in which case a booster is recommended 4 weeks later.
How effective is the vaccine?
Before registering RHDV1 K5 for use in wild rabbit control, a NSW Department of Primary Industries pilot study through the Invasive Animals CRC examined the vaccine for suitability in protecting domestic and production rabbits from RHDV1 K5. This experiment compared the mortality of a small number of vaccinated and unvaccinated rabbits that were subsequently infected with a high dose of K5.
All of the rabbits vaccinated with the currently available vaccine survived the infection with RHDV1 K5. None of the unvaccinated rabbits survived.
This experiment indicates that the currently registered vaccine will protect pet rabbits against RHDV1 K5.
More information is available at Pestsmart.
Purchasing RHDV1 K5 to control rabbits
Authorised users include those holding a Commercial Operators Licence with vermin destroyers’ endorsement or Pest Control Licences authorising the use of pesticides formulated for the control of pest animals. Authorised users for aerial application are those holding a Pilot (Chemical Rating) Licence. In other situations, the use of RHDV1 K5 is not restricted, meaning it may be used and supplied to any person within Victoria.
Landholders can contact EMAI directly on (02) 4640 6337 to purchase RHDV1 K5.
Release sites for Victoria, during the March 2017 national release
How RHDV1 spreads naturally
RHDV1 K5 and the Czech strain of RHDV1 is spread by insect vectors, such as bushflies and blowflies. Direct contact between a rabbit and a rabbit carcass with RHDV is also an avenue of spread. Animals that predate on rabbit carcasses such as foxes, dogs and cats may also excrete the virus in their faeces.
An exotic RHDV called RHDV2 is also circulating within the Australian landscape, after being first reported as a biosecurity outbreak in wild rabbits in May 2015. We now know this virus has spread throughout most of Australia and is currently the dominant circulating RHDV at a national scale.
RHDV2 is the first ever form of RHDV that is not 100 per cent species specific, as it has been detected in hares. It is currently unclear if these were rare spillover infections from rabbits to hares, or if RHDV2 actually spreads effectively between hares, like it does rabbits.
In contrast to RHDV1 K5 and the Czech strain of RHDV1, RHDV2 can cause death in young rabbit kittens (3 to 4 weeks) and vaccinated adults. Importantly, the existing vaccine that is effective against RHDV1 K5 and the Czech strain of RHDV1 may only provide partial protection against RHDV2.