A virus is being used to cull the rabbit population in Australia. But will it affect other animals and spoil the ecosystem?
A serious debate has been going on since
1995 among virologists and wildlife
biologists whether the rabbit calicivirus
(RCV), which causes blood to clot in the
lungs, heart and kidneys of the rabbits,
and results in their death is acceptable as
an efficient way for getting
rid of the rabbit menace
(New Scientist, Vol 153, No 2070).
The debate started soon after the Australian government scientists deliberately released RCV from Wardang Island of the South
Australian coast in October 1995 on the mainland where
rabbits are regarded as the lowest vermin.
The European rabbit (Oryctolagus cuniculus) originated in Spain. In 1859, rabbits were brought to
Australia, where, with few
competitors or predators,
they colonised the country at a rate of
between 20 and 100 kilometres a year,
the fastest known for an mammal other than humans. According
to a 1995 study for the International
Wool Secretariat, an industry group
based in Melbourne, rabbits cost
the country about Australian $600
million per year in lost agricultural production.
Rabbits have played havoc with
Australia's indigenous wildlife. Their
burrows contribute to soil erosion and
they eat growing shoots, preventing
many plants and trees from regenerating. Birds, insects and animals that
depend on this vegetation for food and
shelter, die. For example, the bilby or
rabbit-eared bandicoot, which is classified by the World Conservation Union as a 'vulnerable' mammal species, now
survives only in rabbit-free pockets of land.
When RCV escaped to the mainland
from Wardang Island, to many it
seemed a godsend. The Australian
authorities seized the moment and
after analysing the safety implications,
followed up with deliberate releases
of the virus from 327 sites across Australia.
In fact New Zealand's ministry of
agriculture began public consultations
on whether to import the virus. But
many scientists, particularly in Europe
and North America, oppose the control
strategy and have voiced their disagreement. "We just don't know enough
about this virus. They should hold back
until we know more. Once you've let it
out you can't bolt the door," says clinical virologist David Cubitt of Great
Ormond Street Hospital in London.
Cubitt and others fear that in desperation to rid their country of a plague,
Australian virologists and wildlife biologists have thrown caution to the winds and released a virus that may prove
deadly to Australia's native wildlife.
The demise of rabbits has "devastated
the ecology in Europe", says Diana Bell,
head of the rabbit research group at the
University of East Anglia in Norwich. In
Spain, where wild rabbits are the staple
prey of at least 29 predators, RCV has
halved the rabbit population, which is
an important food source, says Rafael
Villafuerte of Donana Biological
Research Station, in Seville. And there's
great concern, he says, that the threatened Iberian Lynx and Spanish Imperial eagle, animals that are far more dependent on rabbits, are also suffering. In the worst hit parts of Britain, polecats and
wildcats, which eat rabbit, as well as
creatures like the stone curlew, and butterflies that flourish on short-cropped
grass may also be adversely affected, says
Roger Trout, a rabbit expert and private
consultant based in Farnham, Surrey.
Bell says she recognises that Australia
must tackle its considerable rabbit
problem, but she questions the wisdom
of using a still mysterious virus to do the job.
Rabbit and others say that to justify
releasing the virus in the first place, the
Australian government should have first
obtained clear proof that it infects just
one species, the rabbit.
Researchers claim to have done just
that. Between 1991 and 1996, they
exposed 31 species of native and domestic animal to the virus. Samples from
two New Zealand species
that had been exposed to the
virus were sent to the
Australian Animal Health
Laboratory (AAHL) for analysis. The researchers measured the amount of anti- bodies and virus in the blood
and organs of these animals.
They also looked for any
signs of sickness. According
to the researchers, these tests
showed that the virus did not
replicate or cause disease in any test animal.
Alvin Smith of the College of Veterinary Medicine at
Oregon State University, argues that the doses of the
virus used were too low and they were
administered incorrectly. The AAHL
scientists are equally as adamant that
the tests were adequate. "The dose was
chosen as sufficiently large to present a
realistic challenge," says Harvey West-
bury, who oversaw the studies. Each
animal was injected in its muscles with a
dose of virus 1,000 times the amount
that would kill 50 per cent of rabbits.
Over the next four years, the
Agriculture and Resource Management
Council of Australia and New Zealand
plans to solve some of the great
unknowns about RCV release and the
Australian environment. It will monitor
RCV's impact on wild populations of
introduced animals as well as native animals such as bandicoots, wallabies and native mice, in areas around Australia.
It will be at least a year before the
Council will know for certain how animal populations are changing, longer
for hard data on changes in vegetation,
says Mary Bomford, the biologist who
is coordinating the monitoring programme.
The only point on which almost all
experts agree, is that Australia's rabbits
will develop some resistance to RCV.
Brian Cooke, an ecologist, says that the
population which may have already
been reduced from 200 or 300 million
animals to 100 million could recover.
"It will give us some breathing space,"
he adds. Others say that only if
the Australian government supports
additional rabbit control measures,
such as fumigating and ripping up
burrows, while populations are at
their most vulnerable, can this menace
be contained.
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