Calicivirus has not been released in the first half of 2021, and it is unlikely that releases will take place in 2021. In normal years, releases typically take place between late summer and autumn, however releases may take place at other times if conditions are appropriate. The annual release of calicivirus is dictated by a number of factors, including:
- Environmental conditions. The wet summer season led to a high volume of available feed (grass) for rabbits. The ongoing abundance of food means that rabbits are less likely to take calicivirus treated bait.
- Young rabbits become immune. Young rabbits (up to 8 weeks) can become infected with calicivirus, however they have a natural immunity at this age. In fact, rabbits who are exposed to calicivirus within their first 8 weeks will become immune to caliciviruses for the remainder of their lives. Therefore, a release of calicivirus this year, corresponding with a period of high juvenile rabbit numbers may have a negative impact on the efficacy of future release efforts.
- Transmission of caliciviruses through insects. Insects are a large contributing factor to the successful spread of calicivirus, as they can carry the virus from one rabbit to another. The colder weather we are experiencing heading into winter results in a large drop in insect numbers, making any release of calicivirus less successful and potentially ineffective.
Despite not being released this year, calicivirus is present in the Tasmanian environment and may impact rabbit populations in some areas of the state.
Rabbit haemorrhagic disease virus (RHDV1)
Biological control (where available) is an important component of holistic management of a pest species. When rabbit numbers increase and cause significant impact, Biosecurity Tasmania actively releases one strain of rabbit haemorrhagic disease virus (or rabbit calicivirus), RHDV1-K5, to achieve localised rabbit control.
RHDV1 is a viral disease which only affects European rabbits. It was introduced into Australia in 1996 and Tasmania in 1997, and since then it has spread throughout most of the country. But the effectiveness of a biological control agent reduces over time (called host-parasite co-evolution), so research has been undertaken to find a different strain of the virus to release, to boost effectiveness.
From 2017, after more than 10 years of testing (through the Invasive Animals Cooperative Research Centre RHD Boost Project), a variant of the existing calicivirus, known as RHDV1-K5, was released into wild rabbit populations.
RHDV1 and RHDV1-K5 are different strains of the same calicivirus.
Despite the name similarities, and the similar modes of death, RHDV1 and RHDV2 are different types of caliciviruses.
RHDV1-K5 only affects European rabbits and is a naturally occurring variant of the original strain (RHDV1). RHDV1-K5 poses no risk to human health or other non-target species. However, domestic rabbits and farmed rabbits are susceptible.
It is recommended that domestic rabbit owners and commercial rabbit breeders consult their local veterinarian about vaccinations and provide additional protection against the virus by keeping rabbits inside or in insect-proof enclosures.
How is RHDV1-K5 Delivered?
In Tasmania, the RHDV1-K5 virus is introduced using baited carrots. Use of the RHDV1-K5 virus is restricted to trained Biosecurity Tasmania staff and other people who are assessed as competent.
RHDV1 is widespread in rabbit populations in Tasmania. The release of the virus may not be the best control option in all situations; it is only considered for use in areas where:
Protecting domestic and farmed rabbits from calici virus
- other control techniques are not suitable; and,
- there has been no evidence of RHDV1 for over 12 months.
How Does Calicivirus affect rabbits?
A rabbit infected with RHDV1 will develop the disease within one to three days. Greater than 75 per cent of infected rabbits will die from the disease. Infected rabbits end up with ‘cold-like’ symptoms, become lethargic and then die quickly from multiple organ failure.
It should be noted that some rabbits die very quickly from the disease and can look relatively normal externally. They may also show very few visible changes to the internal organs.
Generally, only rabbits older than 12 weeks are susceptible to the RHDV1 and RHDV1-K5. Rabbits younger than 12 weeks that are infected are less likely to die than older rabbits. Young rabbits that survive infection become immune adults.
Vaccine for domestic rabbits
The vaccine that is used to protect rabbits from RHDV1 (Cylap®) also works with RHDV1-K5 and can be provided by your local vet. Validation trials by the NSW Department of Primary Industries demonstrated that all rabbits vaccinated with the current vaccine survived infection with RHDV-K5 whilst none of the unvaccinated rabbits survived.
The RHDV1 vaccine is safe to use on pet and farmed rabbits. As with any vaccine for animals or humans, only vaccinate your rabbit when it is healthy.
Your veterinarian can advise on other issues to be aware of when having your rabbit vaccinated.
Protecting your pet and farmed rabbits from RHDV
An outbreak of another calicivirus known as RHDV2, for which the origin is unknown and there is no available vaccine, may put pet and farmed rabbit stock at risk in Tasmania.
Effects on other species
There is no scientific evidence that RHDV1 infects any other animals.
Australia has tested for the virus in at least 33 representative animal species, domesticated and wild, native and feral. All were given large doses of the virus and no signs of infection were observed. Worldwide, 43 different species have been tested and the virus did not infect any of them.
No evidence of RHDV1 infection has ever been reported for humans. International laboratories confirm that human infection with RHDV is not known to occur and no health effects have been seen, even in people working very closely with the virus.
In addition to rabbits, RHDV2 has been detected in hares in Europe.
RHDV1 K5 Tasmanian release sites - 2021
Note: There are no sites in 2021 - calicivirus has not been released in 2021.
RHDV1 K5 Tasmanian release sites - 2020
RHDV1 K5 was carried out at these locations in 2020:
Eagle Hawk Neck