K5 Rabbit Calicivirus

Updated June 6, 2021


  • It now seems clear that the K5 release was not very significant to pet rabbits (as we predicted!)
  • There is more evidence that the current Cylap vaccine is effective. A further study (reference below) has demonstrated 100% protection in a small group of rabbits experimentally exposed to K5 virus.

In early March 2017, the new K5 strain of calicivirus is planned to be released at 600 sites across Australia and 45 in South Australia. Here’s what pet rabbit owners need to know.

What Is K5 Rabbit Calicivirus?

K5 is a Korean rabbit calicivirus deliberately selected to kill more rabbits in cooler and wetter areas such as the Adelaide Hills and South East Australia. Whatever you think about the needs of farmers, it’s a time of great concern for pet rabbit lovers.

Confusingly, there have been four other calicivirus strains in the news.

  • The ‘classic’ Czech strain of Rabbit Haemorrhagic Disease Virus released in 1995.
  • A Chinese RHDVa strain was found in NSW in 2014 and is of uncertain significance.
  • RHDV2 calicivirus spread into Adelaide in February 2016: follow the link to read more.
  • Cats get an unrelated calicivirus and are not affected by the rabbit virus.

Death occurs rapidly, typically in 1-2 days, often without obvious warning signs. Rabbits may show symptoms of listlessness and poor appetite. The rapid onset of illness has led some authorities to suggest that calicivirus is a humane form of rabbit control. I disagree; as a vet, I believe the only humane death is an instantaneous one.

How To Protect Pet Rabbits From Calicivirus

  • Vaccination is likely to be protective, based on a small study.
  • Flies and other insects are know to spread the virus. Use insect repellents and fly screens around rabbit enclosures, and try to keep unprotected rabbits inside.
  • Prevent contact with wild rabbits (including grass or hay where wild rabbits feed).
  • Practise good rabbit flea & parasite control.
  • Clean hands and any items in contact with rabbits or rabbit faeces, especially shoes.
  • Isolate new arrivals and infected rabbits; please contact us in SA with any suspected deaths.

K5 & The Australian Calicivirus Vaccine

There is some hope that the existing Cylap vaccine will continue to protect rabbits against K5.

Vaccine protection of rabbits against the new RHDV2 has been disappointing. However, the K5 strain is more closely related to the classic strain from which the vaccine was originally developed.

In very small Australian trial the vaccine protected rabbits against exposure to K5. Although the evidence is only sketchy, I expect the vaccine to work this time. Here’s what we are recommending to vaccinate rabbits against K5 calicivirus:

  1. Vaccination at 8 and 12 weeks of age
  2. Annual vaccination thereafter

Note that this contradicts 6-monthly Australian Veterinary Association advice (developed for RHDV2) but is in accordance with the manufacturer’s guidelines for the original Czech strain.

Lastly, don’t panic. I hope I’m not proved wrong, but my gut instincts tell me that this release will be ‘disappointing’ for those interested in rabbit control. In other words, a relief for you and I. Please get your rabbit vaccinated!

Vaccine challenge study ( copies available on request): Read, A. and Kirkland, P. (2017), Efficacy of a commercial vaccine against different strains of rabbit haemorrhagic disease virus. Aust Vet J, 95: 223–226.

Have something to add? Comments (if open) will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.

One Reply to “K5 Rabbit Calicivirus”

  1. As we rush closer and closer to the release of K5 , there are grave doubts re the efficacy of the Czech Strain1351 vaccine Cylap (R) for K5 which is a CHINESE Va strain. It is a different genome family to Czech Strain. The Government claims that Cylap(R) protects using “correct vaccination protocols” , that is not proven, i.e. the testing was for 30 DAYs as per the first paragraph in the conclusion of the pilot study report, but the protocols require 1ml per 12 months. (not 30 days which is all the pilot study tested)

    And only 7 rabbits in two groups, and not monitored long enough, i.e. only 7 days as per 14 days by Pfizer.

    So the Government does NOT know if Cylap (R) will protect and so is willing to risk the lives of thousands of pets to achieve their political objectives.
    Earlier outbreaks from virus strains in the same subgroup have caused significant deaths among vaccinated rabbits– the proof is out there and we should all be worried.

    We have been trying to talk to everybody from Joyce down to the researchers themselves for a couple of years now but they all ignore us and the scientific evidence! That is, science has become subservient to politics , which is not meant to happen. On the recent Channel 7 news item, K5 was described as the “King of Killer virusus… and that it would kill like the myxo did in the fifties, which caused billions of rabbits to die. K5 was chosen because it works well in cooler weather as well, it was chosen because it overcomes Natural immunity …. so does it also overcome vaccinated rabbits… well the earlier outbreak of Chinese Va strain, would indicate that this is the reality of K5. Now to compound the current situation we now have a shortage of vaccine available in some areas it seems. Why does this matter if its not going to work very well? It matters for two very valid reasons, one being that the RHDV351 Czech still kills, and two, we don’t know how much or how little efficacy the vaccine will have for K5…. it is thought given the ratio of deaths in previous outbreaks it wont be very much… BUT, A LITTLE PROTECTION IS BETTER THAN NONE…. but its not good enough, a little for long term is it? If this were cats or dogs, people would be in an uproar demanding suitable vaccines, but guess what, the Government is already planning bio -control for cats….. for feral cats…. BUT big difference , domestic cat owners WILL HAVE A VACCINE… so …. I don’t think its UNREASONABLE TO ASK FOR A DELAY OF K5 until we get a vaccine for the strains killing domestic pets already, RHDV2 (not species specific ) and for K5….. It is noted that this practice has the labelled use of the Cylap(R) vaccine and this is very reassuring as I believe that the Off-label regime is risky and remember K5 was tested against old vaccine for 30 days not for the 12 months that a vaccine should test out to. What does this all mean? Follow this vets advice , its good advice and ask you local MP to lobby to stop the release until we have a vaccine with Proven efficacy. not a ” it may help ” or “its probable”” to find out how to help,,, go to the Against K5 group on FB,its a public group so you don’t even have to be a member to read it… lots of information in the files section. and do the best bio as advised above by Andrew, you possibly can and love your bunnies…. may they stay safe.

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