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  5. What is rabbit calicivirus and how do I protect my rabbit from rabbit haemorrhagic disease?
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What is rabbit calicivirus and how do I protect my rabbit from rabbit haemorrhagic disease?

Rabbit haemorrhagic disease (RHD) is caused by the rabbit haemorrhagic disease virus (RHDV), a type of calicivirus which is typically fatal in non-immune rabbits. There are currently three pathogenic types of this virus in wild rabbit populations in Australia. Rabbit owners should talk to their veterinarian about making sure their rabbits are vaccinated with a vaccine that will protect against both RHDV1 and RHDV2 types, where possible. Veterinarians should follow current  Australian Veterinary Association guidelines (updated in 2022)  to maximise vaccine protection.

Release of RHDV in Australia

The first type of RHDV, known as the Czech type (belonging to the RHDV1 family), was released by the government in 1996 to help control wild rabbits in an effort to minimise environmental damage being caused. This followed an accidental release of the virus in 1995 from CSIRO field trials on Wardang Island in South Australia. An effective vaccine, Cylap® has been available for many years to protect domestic rabbits against this type of the virus.

In recent years, the Czech type has had less impact on wild rabbit populations due to the development of immunity, so Australian scientists have evaluated a number of different RHDV variants for release. From this evaluation, a new type was selected known as the Korean type or K5 (belonging to the RHDV1a family), which was released in early March 2017 at 600 sites across Australia and is now present in many locations across Australia (you can see the current map of reported virus detection here). This new type, which was found to be more infectious than the Czech type, also causes RHD and death in non-immune rabbits. A pilot study to evaluate the effectiveness of the Cylap® vaccine against K5 has indicated that this vaccine will provide protection but further trials need to be undertaken to obtain conclusive results. All rabbit owners are advised to ensure their rabbits are vaccinated before K5 is released.

RHDV2 outbreaks

Another type of RHDV, known as RHDV2, was first confirmed in a wild rabbit in Canberra in 2015, with authorities unable to state the source of the infection. Over the past eighteen months, it has caused the same type of disease and deaths in wild and domesticated rabbits in NSW, ACT, Victoria, South Australia, Tasmania, Northern Territory and Western Australia. No validated trials have been conducted to test the Cylap® vaccine against RHDV2 and there are many reports of vaccinated rabbits dying from infection with RHDV2. Thus, all domesticated rabbits, including those who are vaccinated, are at a high risk of becoming ill and dying from RHDV2, if they are exposed to the virus. Young rabbits (3-4 weeks of age) are particularly vulnerable.

Filavac VHD K C + V is an inactivated bivalent vaccine for rabbits which protects against RHDV types 1 and 2, and was licenced for use in Australia in mid-2022.

Overview of RHDV types

NameTypePresence in AustraliaDisease & death of rabbitsVaccination protection with Cylap®Vaccination protection with Filavac VHD K C + V
Czech (original classic or v351)RHDV1Accidental release in 1995 

Controlled release in 1996
Mainly adults as young are more resistant to diseaseYesYes
K5 (Korean)RHDV1aReleased in March 2017Mainly adults as young are more resistant to diseasePilot study indicates protection* - vaccination is recommendedYes
RHDV2RHDV2Source unknown. First appeared in ACT in 2015; now reported in all Australian states and territoriesVery young rabbits most susceptible with death likelyLow# - modified vaccination protocol may provide some protectionYes

* Note: A small pilot study done in New South Wales showed that all vaccinated rabbits survived infection whereas all unvaccinated rabbits died; however, further research is needed.

# Based on many reports of deaths in vaccinated rabbits from outbreaks in several states.

What are the symptoms of RHDV?

RHDV damages internal organs such as the liver and intestines and may cause bleeding. Signs include fever, restlessness, lethargy and poor appetite with bleeding from the nose and/or blood on the floor where rabbits are housed. Often infected rabbits will show no signs and die suddenly. If a pet rabbit is showing signs, a veterinarian should be contacted immediately. There is no cure for RHD but affected rabbits can be given supportive treatment.

How does RHDV spread?

All RHDV types can spread easily from infected rabbits in droppings, urine, secretions from the eyes and nose, and at mating. Spread can also occur from contaminated objects such as food, clothing, cages, equipment, insects (especially flies), birds and rodents. The virus can survive in the environment for three and a half months over hotter periods but up to seven and a half months in moderate temperatures.

How can I protect my pet rabbit against RHDV?

Rabbit owners should ensure their rabbits are vaccinated to protect them against RHDV. Veterinarians should follow current Australian Veterinary Association guidelines to maximise vaccine protection.

To protect your rabbits against both RHDV types 1 and 2, they can be vaccinated with the Filavac VHD K C + V vaccine. Filavac can be given from 10 weeks of age and one dose of the vaccine provides immunity in seven days and which lasts for 12 months. The Filavac vaccine can produce some side effects, including fever, lethargy, and a temporary lump under the skin at the vaccination site. Rabbits should be vaccinated every year to keep them protected.  Regular six-monthly health checks are also advised for rabbits.

Many rabbits will have been previously vaccinated with the Cylap® vaccination which is effective against RHDV1 but not RHDV 2. If your rabbit has been vaccinated with Cylap® and you want them to have the Filavac VHD K C + V vaccination, the AVA guidelines state that the Filavac vaccine can be given from the next vaccination due date (i.e., 6 months after your rabbit had their last Cylap® vaccination, or earlier in specific circumstances such as an RHDV2 outbreak).

In addition to the information in the AVA policy and guidelines on vaccination of rabbits and ferrets, more information can be found on the AVA website here.

No vaccination is 100% effective at preventing infection, and additional precautions should be taken to help to prevent infection (see below), As well as vaccination, to further protect your rabbits.

Reducing the risk of RHDV infection

RHDV can remain in the environment for an extended period and can be transmitted on objects and via some insects. The following precautions can reduce the risk of infection:

  • Keep your pet rabbit indoors
  • Rabbit-proof your backyard to prevent access by wild rabbits
  • Regularly decontaminate equipment and materials including cages, hutches, bowls etc, with either 10% bleach or 10% sodium hydroxide
  • Limit contact between and handling of unfamiliar pet rabbits
  • Decontaminate hands, shoes and clothing after handling other than your own rabbits
  • Control fleas
  • Control insects (especially flies) as much as possible both indoors and outdoors
  • Remove uneaten food on a daily basis.

Also Read

Updated on January 5, 2023
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https://kb.rspca.org.au/knowledge-base/what-is-rabbit-calicivirus-and-how-do-i-protect-my-rabbit-from-rabbit-haemorrhagic-disease/

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