In this section
What is RHDV1 K5?
RHDV1 K5 is a variant of rabbit haemorrhagic disease virus (RHDV1), which causes a fatal haemorrhagic disease in the European rabbit (Oryctolagus cuniculus). It is specific to the European rabbit, and once a rabbit shows symptoms, death is rapid. There is no treatment or cure for rabbit haemorrhagic disease (RHD). However, a vaccine is available for domestic and production rabbits.
Where will RHDV1 K5 work best?
We expect RHDV1 K5 to work in all areas where rabbits are found. An endemic benign virus is found across New Zealand and in the cool–wet regions of Australia that temporarily protects rabbits from the current RHDV1 strain. RHDV1 K5 can overcome this protection, so we expect to see the greatest benefits in areas where the benign virus is most common.
What type of knockdown will K5 achieve?
While exact knockdown figures are unknown, we expect there will be improved rabbit control in those areas where the current strain of RHDV1 is less effective. This could result in anywhere up to 40% improvement above the current strain and will depend on the location of the rabbit population and the number of susceptible animals within the population
Is it safe (people, pets, wildlife and livestock)?
Yes. No variant of RHDV1 has ever been found to cause infection in humans or any other animal except the European rabbit (Oryctolagus cuniculus). Even predatory animals that eat rabbits that have died from RHDV1 do not develop an infection.
Does it affect other animals?
No. RHDV1 only causes infection in rabbits, and only in the European rabbit (Oryctolagus cuniculus). No other animal has ever developed an infection from being exposed to RHDV1.
I have a pet rabbit. Is there a vaccine available?
Yes. A vaccine (Cylap) is available in New Zealand which has been helping to protect rabbits from the current RHDV1 for many years. Studies undertaken by the Australian government have indicated that this vaccine will also help to protect domestic rabbits against the RHDV1 K5 strain. Pet rabbit owners are advised to discuss this with their veterinarian to ensure their rabbit has the best protection available. Zoetis, the manufacture of the vaccine has confirmed that additional vaccine supplies are being made available in New Zealand. See: What about my pet rabbit?
What are the problems associated with rabbits?
Rabbits pose a significant threat to farming in semi-arid, rabbit-prone country in New Zealand and are estimated to cost over $100 million in lost agricultural production every year. Rabbits compete with grazing stock for food, contribute to soil erosion and water quality degradation, and destabilise the structural integrity of the land, potentially leading to injury of livestock. Rabbits are the staple diet for predators of native wildlife, including ferrets, which act as vectors for the spread of bovine tuberculosis. Toxin-based rabbit control is costly (around $150 per hectare) and imposes temporary restrictions on land use because the land must be kept clear of livestock until all toxin has degraded.
Rabbits are a rural agricultural issue. Why should I care?
Rabbits are not only an issue for agriculture. Rabbits occur in urban environments, such as cemeteries, golf courses, along railway tracks and in parks. They also have an impact on home gardens, restoration plantings and horticultural businesses (including vineyards).
What is the cost of rabbits to the environment?
Currently there is no dollar value on the impact of rabbits on the New Zealand environment, but their impact is known to be significant. Rabbits contribute to soil erosion and subsequent water quality degradation. They can limit the regenerative ability of many plants and plant communities, including endangered species, and can support populations of introduced predators that also prey on native wildlife.
How is RHDV1 K5 different to the current variant of calicivirus?
Both variants cause the same disease, but the RHDV1 K5 variant is better adapted to overcome the protective effects of the benign calicivirus detected in New Zealand rabbits. These benign viruses can temporarily protect rabbits from being infected with our current variant of RHDV1. The benign virus is found throughout New Zealand, including areas where RHDV1 has not worked well in the past. The use of the RHDV1 K5 variant should improve the effectiveness of RHDV1 and continue to suppress rabbit numbers throughout their distribution, particularly when used in conjunction with other forms of control.
How do rabbits with RHD die?
Rabbits that are infected with RHDV1 first develop symptoms anywhere from 24 to 72 hours after infection, and usually succumb within 6 to 36 hours after the first symptoms appear. Many infected animals show no signs of disease and die suddenly. Some animals may exhibit lethargy or excitement before death. Most animals die from the rapid onset of multiple organ failure. Given the short disease time and the sudden death from rapid organ failure, RHDV continues to be one of the more humane control methods for rabbits.
How does RHDV spread naturally?
RHDV is spread by contact of rabbits with infected materials (such as faeces or bedding material), and by insect vectors such as carrion flies 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 hawks, ferrets and cats may also excrete the virus in their faeces.
Is there any advantage in assisting the spread of RHDV K5?
At the RHDV1 K5 release sites please leave rabbits and rabbit carcasses undisturbed for 6 weeks after the release so that the new strain virus can become well established. After that time landowners may wish to assist with the spread of RHDV1 K5 by moving rabbit carcasses locally to help ensure the virus reaches as many rabbit populations as possible and that as great a knockdown as possible is achieved. Landowners should then take advantage of this knockdown by following up with conventional control tools to achieve sustainable long-term control.
Is RHDV1 the same virus as rabbit calicivirus (RCV), rabbit calicivirus disease (RCD), rabbit haemorrhagic disease virus (RHDV), Czech strain and original strain?
There is a whole family of viruses called rabbit caliciviruses. All the above names have been used in the past to describe the original strain of lethal rabbit calicivirus that was released in New Zealand in 1997. RHDV1 is the up-to-date name, used to distinguish it from benign rabbit caliciviruses (RCV-A1) that are found in New Zealand and Australia but are not lethal to rabbits, and from a strain called RHDV2, which is found in Australia and Europe but not here.
Is RHDV1 K5 a GMO (genetically modified organism)?
No. RHDV1 K5 is not a GMO. It is a naturally occurring variant of RHDV1, originally found in a rabbit breeding farm in Korea.
Will the virus mutate and jump species?
No. All evidence to date from 40 countries across 30 years confirms that the present host range of RHDV1 is restricted to just the European rabbit and this is unlikely to change. Variations in nucleotide sequence occur as part of the normal process of evolution in all viruses, but the likelihood of changes that would cause a change in host is low. Caliciviruses maintain very restricted host ranges and the RHDV1 genome is more stable than other caliciviruses.
Will RHDV1 K5 infect pet rabbits?
Yes, all European rabbits, including domestic rabbits, can be infected with the current RHDV1 Czech strain or RHDV1 K5. Pet rabbit owners are advised to discuss vaccination with their veterinarian.
Will there be problems for threatened native species due to fluctuations in rabbit numbers causing prey switching?
Rabbit numbers already fluctuate over time due to variations in climate, conventional control and outbreaks of the existing RHDV1 strains. The Department of Conservation currently undertakes predator control to protect sensitive areas and populations of native species, and will be kept informed about any proposed releases of RHDV1 K5. Any increase in prey switching following the release of RHDV1 K5 is expected to be minor.
How will RHDV1 K5 be used?
The RHDV1 K5 product will be mixed with carrot or oat baits, which will be spread at identified rabbit-prone sites following advice from participating regional and district councils. For the initial nationwide release beginning in March 2018, rabbit populations will be targeted at about 350 sites across New Zealand.
Why not use a bounty to control rabbits?
Attempts to use bounties or commercial harvesting to control rabbits have been tried in New Zealand and Australia before without success. For hunting to be commercially sustainable, rabbit numbers need to be at high densities and this does not prevent the damage done by rabbits or halt land degradation.
Why not use RHDV2 as a biocontrol agent for rabbits in New Zealand?
RHDV2 is a new virus that was originally discovered in Europe and arrived in Australia in 2015. RHDV2 causes RHD-like symptoms but it is a different species of lagovirus and not a variant of RHDV1. RHDV2 affects European rabbits and also some species of hares. Rabbits infected with RHDV2 are less likely to die (5-70% lethality compared to 70-90-% lethality for RHDV1) and take longer to die. Concerns over target-specificity, lower efficacy, and animal welfare impacts removed RHDV2 from consideration as a biocontrol agent. Also the current vaccine that protects pet rabbits against RHDV1 infection is not very effective for protecting against RHDV2.
What is happening at the moment?
Approvals were granted for release in Australia, and a nationwide release programme began in March 2017.
In New Zealand, as part of a national consortium of pest management agencies, Environment Canterbury has led a programme to import and release the new strain, RHDV1 K5 and regulatory approval was granted in February 2018. The consortium, that includes regional councils, Federated Farmers, the Department of Conservation and Land Information New Zealand, is to undertake a nationwide release of the new strain in March and April 2018.
To maximise the effectiveness of the RHDV1 K5, regional councils and researchers have worked with landowners, farmers and other stakeholders to develop a national release strategy. Research shows that autumn is the optimal time to release the virus as immune young rabbit numbers are low and important vectors, such as flies, are active. A controlled release will ensure a high quality commercially prepared product is used at the right time of year and that essential monitoring to measure impacts is in place. These actions will assist to safeguard the potential introduction of further biological control agents in the future.
Categorisation of RHDV and related lagoviruses
(adapted from Australian Pesticides and Veterinary Medicines Authority 2015)
RHDV is a naturally occurring RNA-based lagovirus (family Caliciviridae), and was first reported in domestic rabbits in China in 1984. RHDV then spread rapidly and is now considered endemic in most parts of Europe and Asia, and in some parts of Africa. It has also been observed in the Americas. It is endemic in Australia and New Zealand after deliberate releases to control pest European rabbit populations in the 1990s.
The table below explains the differences between some lagoviruses. In this table, bold text is used to indicate the categorisation of RHDV 08Q712 (an RHDVa sub-type of RHDV). It is important to note that different naming conventions have been used by different authors. This has led to inconsistencies and potential confusion regarding categorisation, particularly if a single source is relied upon without an understanding of the extensive body of scientific literature.
RHDV 08Q712 was designated ‘K5’ (the fifth strain trialled from a group of Korean isolates) within ‘Group II’ (Group I consists of ‘classical’ RHDV; Group II consists of RHDVa). It is important to note that these designations could be misinterpreted due to the similarity of ‘RHDV Group II’ to ‘RHDV2’. However, it is clear that RHDV 08Q712 is not an RHDV2 lagovirus. Some authors have also used RHDVb instead of RHDV2, and RHDV1 instead of RHDV.
Comparison of different lagoviruses
|LAGOVIRUS||LAGOVIRUS SUB-TYPES||PATHO-GENICITY||CAPABLE OF INFECTING||RHDV Vaccine|
|RHDV*||‘Classical’ RHDV (genogroups 1–5 (G1–5), Clade 2/C, Clade 3/A or Clade 4/B)
RHDVa (genogroup 6 (G6) or Clade 1/D)
|Pathogenic||European rabbits (Oryctolagus cuniculus)||Protective when used in accordance with label directions for use|
|Benign||European rabbits (Oryctolagus cuniculus)||N/A|
|Pathogenic||European brown hare (Lepus europaeus), mountain hare (Lepus timidus) and Italian hare (Lepus corsicanus)||Not protective when used in accordance with label directions for use|
|Pathogenic||European rabbits (Oryctolagus cuniculus), Sardinian cape hare (Lepus capensis mediterraneus) and Italian hare (Lepus corsicanus)||Not completely protective when used in accordance with label directions for use|
*Includes RHDV1 K5
Source: Australian Pesticides and Veterinary Medicines Authority 2015. Public release summary on the evaluation of rabbit haemorrhagic disease virus, 08Q712 strain in the product RHDV K5, APVMA product no. 80188, December 2015.