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Need info on Australian Rabbit virus

Sun Feb 18 19:58:21 EST 1996

          Michael Rivero (rivero at news.accessone.com) wrote:

          >Does anyone have any info on the man-made virus being used
          >to eradicate the Australian wild rabbits?

          The virus is rabbit calicivirus which causes rabbit
          calicivirus disease (RCD), also known as viral haemorrhagic
          disease of rabbits. The virus is not man-made, but rather is
          a naturally occurring virus that first appeared in China
          around 1985. The virus only affects the European rabbit and
          does not affect any other species, including closely related
          members of the rabbit family such as hares or cottontail
          rabbits. Following its appearance in China, the virus and
          its associated disease spread naturally throughout Europe
          and has recently reached the United Kingdom and Ireland.

          Since introduced European rabbits are a major pest in
          Australia, the Commonwealth Scientific Industrial and
          Research Organisation (CSIRO) embarked upon a research
          programme to assess the potential for rabbit calicivirus as
          a method for biological control of rabbits. The virus being
          used was the natural virus from Eurasia; there were no
          man-made modifications to the virus. The virus was also
          inoculated into 28 species of animals other than rabbits,
          including marsupials, and there was no evidence of infection
          of any species other than rabbits.

          The CSIRO conducted laboratory tests under high level
          security before setting up a field trial on Wardang Island,
          several kilometres off the coast of South Australia, to
          determine the impact of the virus on a naturalised
          population of rabbits. Unfortunately, the virus spread out
          of control from the quarantine area on the island to
          mainland Australia, possibly due to carriage by birds,
          insects or wind. It has affected rabbits in a large area of
          South Australia, particularly in the Flinders Ranges, and
          has spread to western New South Wales and south western

          This accidental release can be viewed from several different
          angles. Most farmers and conservationists see destruction of
          rabbits as beneficial to the Australian environment,
          allowing regeneration of many outgrazed native species of
          plants and reestablishment of populations of endangered
          Australian marsupials. However, there is some concern that
          populations of native predators, such as the wedge-tailed
          eagle, that have successfully adapted to preying upon
          rabbits, may temporarily decline. Also, the predation
          pressure on species unaffected by the virus may be
          increased. At the same time, populations of the introduced
          European (red) fox may decline as the rabbit density
          decreases, with uncertain effects on populations of native

          Another problem is with the timing of the release. Whereas
          the virus causes high mortality in adult rabbits, young
          rabbits are usually unaffected by rabbit calicivirus and
          develop immunity. I do not have a lot of information about
          the pathogenesis of the disease, but understand that death
          of rabbits affected by RCD results from a coagulation
          disorder leading to haemorrhage and in young rabbits this
          response is not well developed. Therefore, the optimal time
          for a controlled release of rabbit calicivirus would be
          outside the breeding season when there are few young
          rabbits. The present outbreak started during the breeding
          season, so the impact of the accidental release may not be
          as great as if release was planned. At this stage there is
          much debate and negotiation about whether to accelerate the
          controlled release programme now that the virus has escaped.

          Groups that have opposed the release of rabbit calicivirus
          include the rabbit fur and meat industry and animal welfare
          groups, for example the Royal Society for Prevention of
          Cruelty to Animals (RSPCA). Rabbits are harvested for their
          fur to be used, for example, in the production of hats. I
          have heard a news report that a hat manufacturer using
          rabbit fur had to import fur from overseas (even though
          there are still plenty of rabbits in Australia in areas that
          the virus has not reached). One company in Australia
          exporting rabbit meat closed down because overseas buyers
          did not want meat from rabbits that may have been exposed to
          rabbit calicivirus (even though there is no risk to humans).
          Concerns about animal welfare must be balanced against the
          negative impact that rabbit calicivirus has had on the
          Australian environment and native species of animal. A
          "frequently asked questions" sheet distributed by the CSIRO
          states that, "After 18 hours of infection with the virus,
          adult rabbits become progressively quieter; and in about
          30-40 hours of being infected they died quietly, with
          minimal apparent stress". Also, there is a precedent in that
          myxomatosis virus has previously been released in Australia
          in an attempt to control rabbits.

          There have been a number of news reports questioning the
          host specificity of rabbit calicivirus, in particular
          because there are other caliciviruses affecting other
          species. For example, Norwalk viruses of humans are
          caliciviruses. Feline calicivirus causes feline infectious
          peritonitis in cats. Vesicular exanthema of pigs is caused
          by a calicivirus that can infect humans and appears to be
          identical to San Miguel sea lion virus, possibly having
          originated from pinnipeds. However, since in the period of
          over 10 years since rabbit calicivirus first appeared there
          has been no evidence that it infects species other than
          rabbits, at this stage I think concerns about transmission
          to humans, for example, are not warranted.

          A vaccine is available to protect domestic and farmed
          rabbits against rabbit calicivirus.

          Adrian W Philbey

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