Rabbit Biocontrol Advisory Group - RCD - Frequently Asked Questions

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RCD - Frequently Asked Questions

How is RCD transmitted to rabbits?

RCD is highly contagious and is spread by contact between susceptible rabbits and an infected rabbit: also by contact with excreta contaminated with the virus. Experimentally, very close contact between rabbits is required for successful transfer.

Carrion-feeding birds could also possibly transmit the virus mechanically by carrying pieces of infected carcass. Predators such as foxes and ferrets may also transmit the virus by shedding it in droppings. These animals do not become sick from the virus.

RCD virus does not multiply in insects. However laboratory studies suggest that insects, such as rabbit fleas and mosquitoes, can spread the virus between rabbits, but only if virus-contaminated insects are in contact with susceptible rabbits within a few hours. It is speculated that bush flies may also transfer the virus mechanically.

How does RCD kill rabbits?

RCD causes the rapid development of blood clots in major organs such as lungs, heart and kidneys. These clots block blood vessels and result in death from heart and respiratory failure in about 30-40 hours.

Does RCD cause suffering before death?

Rabbits infected with rabbit calicivirus in a study at the CSIRO Australian Animal Health Laboratory did not display any visible signs of pain or distress.

After 18 hours of infection with the virus, adult rabbits became progressively quieter; and within about 30-40 hours of being infected they died quietly, with minimal apparent distress.

Some rabbits show an increase in temperature (from approximately 39 degrees C up to 42 degrees C), one day before death and an increase in respiratory rate, just prior to death.

There have been reports from overseas that rabbits with RCD have blood-tinged fluid coming from the nose. In the trials at AAHL, some rabbits had blood-tinged fluid coming from the nose, but only after death.

Are all rabbits affected by rabbit calicivirus?

Rabbit calicivirus causes disease only in European rabbits (Oryctolagus cuniculus) and domestic strains derived from this species. Other rabbit species do not catch the virus or become sick from it. Farmed and pet rabbits in New Zealand would be expected to be fully susceptible to the disease.

Effective vaccines to protect domestic rabbits have been developed in Europe and will be available in New Zealand.

Wild rabbits in the Americas, such as cottontails, jack-rabbits, and volcano rabbits do not catch RCD. A number of other rabbits in the genera Lepus, Sylvilagus, and Thermerolagus have been tested overseas and shown not to be susceptible to experimental inoculation with rabbit calicivirus disease.

RCD is related to European Brown Hare Syndrome (EBHS). However, laboratory studies show that it is impossible to infect rabbits with EBHS virus, or hares with rabbit calicivirus.

Will rabbits develop resistance to RCD?

Studies in Europe on rabbit populations exposed to rabbit calicivirus disease for approximately ten years have not detected any development of genetic resistance of rabbits to the virus. Rabbits and viruses, like every organism contain genetic material that can mutate (under evolutionary pressure).

It is possible, therefore , that rabbits may develop resistance to RCD and/or rabbit calicivirus disease may become less virulent. This has happened with the myxoma virus that causes myxomatosis. If RCD is used as a rabbit control tool, it will not be a "magic bullet". Plans would be developed with land managers to integrate RCD with other control measures, to maximise the long-term impact on rabbit numbers.

How do you recognise a rabbit with RCD?

There are no specific clinical signs (symptoms) in rabbits with RCD. After about 18 hours of infection with rabbit calicivirus, adult rabbits become progressively quieter; within approximately 30-40 hours of being infected they die quietly with minimal apparent distress.

Some rabbits may appear listless and reluctant to move one day after infection and at this stage, some may have an increased temperature (from 39 degrees C up to 42 degrees C). A few hours prior to death, some rabbits have an increased respiratory rate.

How can a vet recognise RCD at post-mortem?

At post-mortem, the major lesions are: a swollen, enlarged spleen; a swollen, friable liver with a lobular pattern; small focal pulmonary haemorrhages that may join to form large reddened areas. Occasionally, only two of these organs may be affected. Myocardial (heart muscle) haemorrhages and renal infarcts(kidney scars) occur more rarely.

Is a vaccine available for domestic rabbits?

Yes. The vaccine is called Cylap HVD and is made by the company Cyanamid in Spain. It has been registered in New Zealand for distribution by veterinary practitioners. Stocks of the vaccine are available for immediate distribution in the event of an accidental or planned introduction. The vaccine will not be available if RCD does not arrive in New Zealand.

Is the vaccine safe?

The vaccine is a "killed-vaccine", therefore it does not contain live virus and it is not dangerous to rabbits. As a standard precaution, the vaccine should not be used in any rabbit showing any kind of sickness. This is standard practice for any vaccine for use in humans and animals.

Is it safe to eat vaccinated rabbits as it is with other vaccinated stock?

Yes.

Are vaccines effective against RCD?

Vaccines were very effective in reducing the incidence of RCD in Europe in the late 1980s. One vaccination can provide lifelong protection, but Cyanamid recommends an annual booster.

Is it necessary to vaccinate the offspring of immune adult rabbits?

Vaccines are produced from virus grown in rabbits. Rabbits are immunised at about ten weeks of age.

Maternal antibodies can be passed to young and confer temporary immunity. Vaccination of young will then provide permanent immunity. The timing of vaccination is critical. Young rabbits are vaccinated at ten weeks of age, when most of their maternal antibody has disappeared.

RCD and the environment

How long does rabbit calicivirus persist in the environment?

Under experimental conditions, the virus can survive up to 225 days at 42 degrees C (on live tissue such as liver), but for only 2 days at 60 degrees C. It has been detected for 105 days at 20 degrees C when dried on cloth. The virus can survive in the pH range 3-8.

Research at CSIRO Australian Animal Health Laboratory showed that rabbit calicivirus disease persisted for less than a month in the artificial warren system (23 degrees C). In the laboratory, rabbit calicivirus disease does not spread across a 50 cm space, so it is unlikely to be spread by wind or water in a natural environment. It needs to be carried on or by some other organism.

The virus may persist for an even shorter period in a natural environment, depending on temperature and sunlight conditions. In trials on Wardang Island, the virus persisted for less than one week in rabbit-free warrens. The virus may persist longer on infected carcasses, but it does not multiply in dead rabbits.

If RCD arrives accidentally in New Zealand, what are the likely environmental consequences?

If an accidental arrival of RCD is not contained, and it becomes an endemic disease, it is likely to reduce rabbit numbers significantly.

There is concern that the widespread deaths of rabbits would result in predators switching to other food sources such as endangered or rare native species.

In most areas, this "prey-switching" factor is unlikely to be significant. However, in some areas, where both rabbit and native prey densities are high, ferret and feral cat control may be necessary.

The long-term effects on native prey are unlikely to be significant. Plans are being developed to deal with any short or medium term impacts of prey switching. These plans will complement predator control work already carried out by the Department of Conservation.

Why was RCD being trialled on Wardang Island?

After the safety of rabbit calicivirus disease was confirmed in three years of laboratory testing, agencies agreed more information was required about its potential effectiveness as a control tool. Trials on Wardang Island were designed to provide this information because it could not be obtained in a laboratory. They were designed to assess the impact and persistence of the virus, its rate of spread between and within warren systems and its humaneness under field conditions.

Wardang Island was the only site in Australia that met the selection criteria for quarantine trials with a biological control agent. Despite extensive precautions, RCD escaped from Wardang Island (not the secure CSIRO Australian Animal Health Laboratory) to the mainland of Australia.

Is there really a rabbit problem in New Zealand?

The European rabbit is New Zealand's second most serious pest (after the brushtail possum). Grazing rabbits compete with livestock for pasture. They kill trees and shrubs. They infest 55% of New Zealand. They contribute to soil erosion by removing vegetation and disturbing soil during burrow construction. Rabbits have probably contributed to the extinction of some native plants.

The cost of control, and production losses, is estimated at a minimum of $22 million dollars per annum in New Zealand. This figure does not account for any of the serious, long-term environmental and conservation damage caused by rabbits.

Australia and New Zealand land managers have attempted to control rabbits with a combination of measures including poisoning, shooting, ripping, blasting, releasing predators, a biological control agent (myxomatosis) and rabbit-proof fencing.

Additional control methods are needed to reduce rabbit numbers significantly, so that conventional control methods, which are labour-intensive, can be more effective.

Would rabbit calicivirus disease eradicate rabbits?

If RCD is approved for release, it would not be a "magic bullet", it would be another tool to add to rabbit controls that are currently in use. Plans to release RCD would be designed with landholders and regional councils to maximise the long-term impact on rabbit numbers.

Why can't we harvest rabbits to control them?

There is a market for wild rabbit meat and skins and several small businesses have now been established supplying the domestic market. While such businesses may be financially viable, there is no evidence that commercial harvesting of rabbits has proved effective in reducing them to low enough numbers to protect the landscape. Shooting removes a portion of the population and is a valuable method after high numbers have been reduced by poisoning. However, these lower density numbers are uneconomic to shoot for harvesting.

Does rabbit calicivirus disease affect other animals?

Rabbit calicivirus disease causes disease only in European rabbits. Other animals are not infected by RCD.

RCD has spread from Asia to Europe and killed millions of rabbits. There are no reports in scientific, or medical, literature that RCD has affected any other animal species that have come into contact with rabbits infected with RCD.

For rabbit calicivirus disease to qualify as a biological control agent in Australia and New Zealand, it must not infect species other than rabbits. A list of animals for testing was developed in consultation with the Australian and New Zealand Environment and Conservation Council (ANZECC).

The Australian trials confirm the evidence from 40 countries that RCD is so specific that no other animals are susceptible. None of the 28 species tested was infected by the virus. All animals were exposed to a thousand rabbit-lethal doses.

The animals chosen for testing included a representative range of New Zealand and Australia fauna. They included the following:

animals: horses, cattle, sheep, deer, goats, pigs, dogs, cats and fowls.
animals: foxes, hares (including New Zealand examples), ferrets, rats and mice.
native mammals: bush rats, spinifex hopping mice, plains rats, fat-tailed dunnarts, northern brown bandicoots, brush-tailed bettongs, tammar wallabies and brushtailed possums.
long-billed corellas, feral pigeons, silver gulls, brown falcons and emus.
common blue-tongue lizards.

Emus and lizards were tested at New Zealand's request. Tests were also conducted on the kiwi - which has a lower blood temperature than other birds - and the short-tail bat, New Zealand's only native land mammal. While the bats were not affected, the kiwis produced a low level of antibodies; a reaction to the amount of foreign protein they were injected with. They were not infected by the rabbit calicivirus disease and the virus did not multiply in the kiwis. During the trials the kiwis continued to thrive and gain weight. The two surviving animals will be returned to DoC's custody. Researchers concluded that RCD was no threat to kiwis.

Does RCD affect humans?

For over 10 years, rabbit calicivirus disease has been widespread throughout Europe and China in wild rabbits and on rabbit farms. During that time, there has been close contact between people and diseased rabbits. No transmission of the virus to humans, or illness related to the virus has been reported in scientific or medical literature. Blood tests, with one possible exception, have not revealed the presence of antibodies of the virus in humans who have had contact with the virus or diseased rabbits.

Could rabbit calicivirus mutate and affect other animals?

Viruses, like all organisms, contain genetic material that can mutate. However, the vast majority of mutations only affect the virus itself and its impact on its host.

Rabbit calicivirus disease is species-specific: no other animals, nor all species of rabbits, are infected, or affected (i.e. can catch or become ill), by the virus.

In over 10 years of field experience with rabbit calicivirus disease, there is no evidence that it has altered to affect any species other than European rabbits. The international scientific literature has reported only one virus of this type that has mutated sufficiently to be able to infect another species (a cat virus to dogs).

This is quite different from those viruses that have the potential to infect a range of species if the conditions for transfer are suitable. The AIDS virus is an example, infecting both primates and humans.

It is therefore highly unlikely that rabbit calicivirus would infect other species.

Are pets safe from rabbit calicivirus disease? (i.e. pets other than rabbits)

Yes. Rabbit calicivirus causes disease only in European rabbits. Wild rabbits in the Americas, for example, cottontails, jack-rabbits, and volcano rabbits, do not catch RCD.

RCD has been tested on a wide range of species including domestic (such as cats and dogs) and feral animals, native mammals, birds and reptiles.

Would it be safe to eat rabbits infected with rabbit calicivirus disease?

It would be safe for humans to eat rabbits infected with RCD. Many humans have been exposed to rabbit calicivirus disease on rabbit farms in Europe and China. There are no reports in scientific or medical literature of anyone catching the virus or becoming sick from it. Health Authorities in the UK and Europe do not restrict the sale of rabbits from farms where the disease has occurred, providing the rabbits sold are healthy. This is the same requirement as for other livestock sold for human consumption.

Is the rabbit disease RHD the same as RCD?

It is the same disease.

Why was "rabbit haemorrhagic disease" (RHD) renamed "rabbit calicivirus disease" (RCD)?

In a three-year study at CSIRO Australian Animal Health Laboratory, rabbits infected with rabbit calicivirus disease did not die from haemorrhaging. "Rabbit Haemorrhagic Disease" is therefore an inaccurate name for the disease. The disease was renamed Rabbit Calicivirus Disease (RCD) because this virus belongs to the virus family Caliciviridae.

Is RCD related to haemorrhagic diseases like that caused by Ebola virus?

No. Rabbit calicivirus disease and Ebola virus are distinctly different viruses. Rabbit calicivirus disease belongs to the "Caliciviridae" family, whereas Ebola virus belongs to the family of viruses called "Filoviridae".

In studies with rabbit calicivirus disease conducted at the CSIRO Australian Animal Health Laboratory, haemorrhages did not cause the death of infected rabbits (and were not a prominent feature). Humans infected with Ebola virus die from severe haemorrhaging of major organs, which is why it is sometimes referred to as a haemorrhagic disease.

What is a calicivirus?

Caliciviruses belong to a family of viruses called "Caliciviridae". This is a diverse group of viruses associated with a range of clinical syndromes. A commonly-known calicivirus is feline calicivirus which causes an influenza-like disease in cats (cat 'flu').

Viruses are not classified by the type of disease signs they produce: classification is based on characteristics such as physico-chemical properties, protein structure, genome organisation and replication strategies of the virus.

Rabbit calicivirus disease has been placed in the Caliciviridae family based on the results of several studies on these types of characteristics.

Is rabbit calicivirus disease genetically engineered?

Rabbit calicivirus is not genetically engineered or made in a laboratory. It is a naturally-occurring virus, prevalent in the northern hemisphere, that was first noted in China in 1984 and Europe in 1986. Recent research indicates RCD may have been present, as a less virulent form, in rabbit populations for many decades.

Do young rabbits infected with rabbit calicivirus become immune to RCD for life?

European rabbits less than six to eight weeks old do not all die from rabbit calicivirus disease,even if they become infected. Evidence suggests that young rabbits develop antibodies, become immune and may survive to become the breeding population in the following year.

Maternal antibodies can be passed to young and confer immunity: however, this immunity is short-lived. The next generation of young become susceptible and RCD can spread through the population again.

This means that, if RCD is introduced in New Zealand, it will be necessary to combine RCD with other control methods to provide effective rabbit control.

Why do young rabbits under 5 to 8 weeks survive RCD?

This is not known, but it is speculated that young kittens have a relatively immature immune system, and cannot produce enough of the chemicals that initiate clotting which causes death in older rabbits.

Is RCD likely to arrive naturally in New Zealand?

RCD is a very tough virus that can survive freezing, and remain infective on fabric for over 100 days at 20 degrees C. It is killed by higher temperatures (over 60 degrees C for two days) and sunlight.

It is unlikely that RCD will be transported to New Zealand on the insects and birds that frequently cross the Tasman. The most likely source of accidental introduction is on goods or livestock arriving from Australia. An illegal introduction cannot be discounted.

As RCD spreads throughout Australia the risk of accidental arrival in New Zealand increases.

Contact for Enquiries

MAF Information Services
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PO Box 2526
Wellington, NEW ZEALAND

Fax: +64 4 894 0721
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RCD - Frequently Asked Questions

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