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
Queensland.
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
marsupials.
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
