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Further developments in calicivirus vaccination protocols in Australia

 

Over the last few years there have been some developments in the strains of calicivirus and calicivirus-like viruses in Australia.  Due to the confusing nature of these new viruses and the general lack of information on their prevalence in Australia there has been a large amount of confusion, particularly regarding vaccinations and protective measures for pet rabbits.  In the interest of keeping all of our clients up to date with current information we compiled all known information and recommendations in this article earlier in the year, and have been in consultation with various government and veterinary agencies through the year in order to ensure that our protocols were consistent with providing good immunity and care for our patients.

The story so far…
In Australia we are able to vaccinate rabbits against RHDV1, the original calicivirus (or rabbit haemorrhagic disease virus) released in Australia in the 90s, with the CYLAP vaccine.  Recently the government has announced it will be releasing a new strain of RHDV1 called RHDVK5 (K5, or the Korean strain) in order to maintain better biocontrol of wild rabbits, who are largely immune to the original strains of RHDV1.  A small pilot study was undertaken prior to the release of K5 which found that rabbits vaccinated with CYLAP were unaffected when infected with K5, though unvaccinated rabbits passed away.  Based on this study it is assumed that CYLAP will provide protection from K5 as well as older strains of RHDV1.

Also present in the wild is the RHDV2 virus.  This is not a new strain of RHDV1, but a calicivirus-like virus which causes a similar disease process.  Strains of RHDV2 has been previously reported in Europe, and a strain has been found in Australia in NSW, Victoria, SA, Tasmania, the ACT, and recently in WA (through personal communication with industry veterinarians we have been informed that the Australian strain is different to well studied European strains).  Use of the CYLAP vaccine to protect against RHDV2 infection has been found to be reasonably effective in Europe, with some vaccinated animals still being susceptible.  The CYLAP vaccine is not specific to RHDV2, and any protection it is giving against this disease is through cross-protection.  As RHDV2 is still relatively new to Australia not much is known regarding how much cross-protection against our specific strain can be gained by vaccinating with CYLAP.  Evidence from studies of common European strains indicate that cross-protection may be as high as 70% (based on communication with government agency veterinarians), however applying this number to the strains present in Australia should be done with a grain of salt.  There also seems to be some anecdotal evidence that older animals (who have had more vaccinations over their lives) are less likely to fall victim to RHDV2.

A note on CYLAP
CYLAP contains deactivated viral particles, which allow the rabbit’s immune system to recognise the qualities of the RHDV1 virus without exposing the rabbit to anything which could cause clinical disease.  This vaccine is registered for 12 monthly use in adult rabbits to prevent calicivirus infection, with 1ml of vaccine being given at a time.  It is recommended that the vaccine is refrigerated, and that unused vaccines in the bottle be discarded after 12 hours, as the efficacy and safety from bacterial contamination cannot be guaranteed outside of these conditions.  CYLAP vaccinations should be administered or overseen by a registered veterinarian.  Alterations to this usage protocol may result in holes in our vaccination protection net.

While CYLAP is a deactivated vaccine it can still have some mild negative effects on the rabbit.  If not given carefully, if given to a stressed rabbit or if given on a hot day it may result in lethargy, inappetence and skin lesions.  In rare occasions lameness may occur.  These conditions are usually transitory and can be managed with pain relief and supportive care.  Vaccination can also be detrimental in animals who have underlying chronic illnesses, as it results in the immune system being redirected from managing the chronic illness while it learns how to fight off RHDV1.  This dip in immune protection may result in a deterioration in overall health in rabbits with chronic dental disease, ear infections, respiratory disease, E cuniculi and other underlying conditions, leading to poorer health in the long term.  For this reason it is important to consult with a veterinarian prior to vaccination in order to fully assess the risks and benefits to your rabbit.  While vaccination is always ideal and recommended, in some cases where rabbits have severe underlying disease it may be better to reduce risk of RHDV1 infection in other ways and vaccinate only when the rabbit is at their healthiest (this may be less frequently than the recommended vaccination protocol).

New news
As of 5 October 2016 the Australian Veterinary Association has changed its vaccination protocols.  Previous recommendations were largely in keeping with the registered use for CYLAP, with yearly vaccinations for adult animals with modifications for younger rabbits to be vaccinated at four, eight and twelve weeks, and with an off-label (non-registered) six monthly use in breeding rabbits (this helps elevate the levels of antibodies passed to their offspring).  The AVA recommendations are now to vaccinate all adult rabbits with the off-label schedule of vaccinations every six months, though they report that there is still no evidence that six monthly vaccinations will provide better protection against K5 or RHDV2 than yearly vaccinations do.  It is also strongly recommended that clients and veterinarians discuss the health of individual rabbits prior to starting a new vaccination protocol.

The Melbourne Rabbit Clinic has been in continuing communication with the AVA to determine the reasoning for this policy change.  We have also spoken to a number of government and industry veterinarians, as well as other exotics veterinarians across Australia in order to collate and synthesise all current information on these viruses.  Based on this communication there seems to be some evidence that though RHDV2 has been reported across more areas of Australia, the frequency of rabbits testing positive for the disease may over time diminish compared to rabbits testing positive for RHDV1.  This follows a similar pattern to European strains of RHDV2, which show an initial elevation in RHDV2 infections followed by a reduction in prevalence and a resurgence in RHDV1.  The pharmaceutical company which produces CYLAP has also indicated that there is no new information which would indicate a benefit to more frequent vaccinations.

What does this mean for us?
Melbourne Rabbit Clinic’s goals are to maintain good evidence-based medicine which will benefit the overall health of our patients.  We aim to follow industry recommendations, while always endeavouring to base our protocols on the most recent research and studies available.  As we only see rabbits and guinea pigs many of our patients come to us with underlying health conditions, which often are quite severe and require significant medical management to control.  Because of this there is some concern that many of our patients will be negatively affected by more frequent vaccinations.

As in all medical protocols vaccinations should be tailored based on the health of each specific patient.  As such we would like to make the decisions on how frequently to vaccinate your pets with you, based on their overall health and risk factors.

We understand that more frequent vaccinations may put pressure on cost-constrained clients.  As such Melbourne Rabbit Clinic are offering reduced six monthly vaccinations so long as the rabbit has been vaccinated and had a full consultation with one of our vets at our clinic in the last 12 months.  Consultations for these vaccinations would be undertaken in partnership between our vets and our highly trained nurses, with a nurse talking to you about how your rabbit is doing and a vet giving them a thorough health check and their vaccination in our treatment room.  We hope that this will allow all clients to make a decision on the vaccination protocol best for their rabbit friends without having to stress about financial issues.

Please contact Melbourne Rabbit Clinic for more information, and organise a health check with one of our vets to discuss the vaccination protocol best for your rabbit.  We will aim to keep you updated with any further developments.

Zoe

associate consulting vetective at melbourne rabbit clinic