RHDV1 K5 in Victoria
European 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.
Rabbit biocontrol programs have existed in Australia since 1950 with the release of the Myxoma virus. It was initially effective, but its impact soon declined as the virus and rabbit populations changed genetically.
In 1996, a Czech strain of Rabbit Haemorrhagic Disease Virus (RHDV1) was released in Australia in another attempt to reduce rabbit populations. While initially effective, many rabbit populations have now developed genetic resistance to the Czech strain. An endemic non-lethal strain of RHDV (RCV-A1) was also found to provide some rabbits with partial protection from virus.
RHD Boost was a national biological control project that sought to identify new (RHDV) variants.
The RHD Boost project involved identifying and evaluating 38 genetically and anti-genetically different RHDV variants. Six of these were selected for further testing, and a Korean variant of rabbit calicivirus called Rabbit Haemorrhagic Disease Virus K5 (RHDV1 K5) was identified as a the favourite.
What is RHDV1 K5?
RHDV1 K5 is a Korean variant of Rabbit Haemorrhagic Disease Virus (RHDV1) that causes a fatal haemorrhagic disease in the European rabbit (Oryctolagus cuniculus). It was selected as part of the RHD Boost program for its ability to overcome some of the shortfalls that had begun to emerge with the original Czech strain of RHDV1. The national release of RHDV1 K5 occurred in March 2017, but not before it was rigorously tested, assessed and registered as part of a strategic collaboration between research providers, government and industry bodies.
During the national release, RHDV1 K5 was released at 323 community monitored sites and 18 intensively monitored sites. RHDV1 K5 produced an average rabbit population knockdown of 34%, but the results were highly variable. It was also discovered that RHDV1 K5 worked more as a biocide, rather than a biocontrol agent. That is, 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 includes a well-designed warren ripping component that is complemented by other control techniques.
How RHDV1 spreads naturally
RHDV1 K5 and the Czech strain of RHDV1 are spread by insect vectors, such as bushflies and blowflies. Direct contact between a rabbit and a rabbit carcass infected 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 without being impacted by the virus themselves.
Where RHDV1 K5 works
RHDV1 K5 works in a range of different habitats, although the most beneficial results will likely be seen in cooler/wetter regions of the state, as this is where the benign strain of the virus (RCV-A1) is found.
RHDV1 K5 is more humane
RHDV1 K5 is one of the more humane methods of controlling wild rabbits. Once contracting the virus, 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.
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. Even predatory animals that eat a rabbit which has died from RHDV1 K5 will not develop an infection. RHDV1 (K5 and the Czech strain) are safe for people, wildlife livestock and all pets except domestic rabbits.
Pet rabbits are affected by both RHDV1 strains, as they are descendants of wild rabbits. Owners of pet rabbits are advised to vaccinate their animals against the virus.
Cylap® is a vaccine available for the prevention of RHDV1 K5 and the Czech strain of RHDV1. This vaccine has been shown to be effective against both strains, 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. After, an annual booster dose and health check is advised. Occasionally, in the face of an outbreak, rabbits may be vaccinated earlier than 10 weeks of age in which case a booster dose is recommended four 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 in partnership with 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.
An exotic RHDV, called RHDV2, is also circulating within the Australian landscape. It was first reported 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 for 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.
Figure 1 courtesy of W Mules