A serious debate has been going on since1995 among virologists and wildlifebiologists whether the rabbit calicivirus(RCV), which causes blood to clot in thelungs, heart and kidneys of the rabbits,and results in their death is acceptable asan efficient way for gettingrid 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 SouthAustralian coast in October 1995 on the mainland whererabbits are regarded as the lowest vermin.
The European rabbit (Oryctolagus cuniculus) originated in Spain. In 1859, rabbits were brought toAustralia, where, with fewcompetitors or predators,they colonised the country at a rate ofbetween 20 and 100 kilometres a year,the fastest known for an mammal other than humans. Accordingto a 1995 study for the InternationalWool Secretariat, an industry groupbased in Melbourne, rabbits costthe country about Australian $600million per year in lost agricultural production.
Rabbits have played havoc withAustralia's indigenous wildlife. Theirburrows contribute to soil erosion andthey eat growing shoots, preventingmany plants and trees from regenerating. Birds, insects and animals thatdepend on this vegetation for food andshelter, die. For example, the bilby orrabbit-eared bandicoot, which is classified by the World Conservation Union as a 'vulnerable' mammal species, nowsurvives only in rabbit-free pockets of land.
When RCV escaped to the mainlandfrom Wardang Island, to many itseemed a godsend. The Australianauthorities seized the moment andafter analysing the safety implications,followed up with deliberate releasesof the virus from 327 sites across Australia.
In fact New Zealand's ministry ofagriculture began public consultationson whether to import the virus. Butmany scientists, particularly in Europeand North America, oppose the controlstrategy and have voiced their disagreement. "We just don't know enoughabout this virus. They should hold backuntil we know more. Once you've let itout you can't bolt the door," says clinical virologist David Cubitt of GreatOrmond 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 provedeadly to Australia's native wildlife.
The demise of rabbits has "devastatedthe ecology in Europe", says Diana Bell,head of the rabbit research group at theUniversity of East Anglia in Norwich. InSpain, where wild rabbits are the stapleprey of at least 29 predators, RCV hashalved the rabbit population, which isan important food source, says RafaelVillafuerte of Donana BiologicalResearch Station, in Seville. And there'sgreat 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 andwildcats, which eat rabbit, as well ascreatures like the stone curlew, and butterflies that flourish on short-croppedgrass may also be adversely affected, saysRoger Trout, a rabbit expert and privateconsultant based in Farnham, Surrey.Bell says she recognises that Australiamust tackle its considerable rabbitproblem, but she questions the wisdomof using a still mysterious virus to do the job.
Rabbit and others say that to justifyreleasing the virus in the first place, theAustralian government should have firstobtained clear proof that it infects justone species, the rabbit.
Researchers claim to have done justthat. Between 1991 and 1996, theyexposed 31 species of native and domestic animal to the virus. Samples fromtwo New Zealand speciesthat had been exposed to thevirus were sent to theAustralian Animal HealthLaboratory (AAHL) for analysis. The researchers measured the amount of anti- bodies and virus in the bloodand organs of these animals.They also looked for anysigns of sickness. Accordingto the researchers, these testsshowed that the virus did notreplicate or cause disease in any test animal.
Alvin Smith of the College of Veterinary Medicine atOregon State University, argues that the doses of thevirus used were too low and they wereadministered incorrectly. The AAHLscientists are equally as adamant thatthe tests were adequate. "The dose waschosen as sufficiently large to present arealistic challenge," says Harvey West-bury, who oversaw the studies. Eachanimal was injected in its muscles with adose of virus 1,000 times the amountthat would kill 50 per cent of rabbits.
Over the next four years, theAgriculture and Resource ManagementCouncil of Australia and New Zealandplans to solve some of the greatunknowns about RCV release and theAustralian environment. It will monitorRCV's impact on wild populations ofintroduced 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 theCouncil will know for certain how animal populations are changing, longerfor hard data on changes in vegetation,says Mary Bomford, the biologist whois coordinating the monitoring programme.
The only point on which almost allexperts agree, is that Australia's rabbitswill develop some resistance to RCV.Brian Cooke, an ecologist, says that thepopulation which may have alreadybeen reduced from 200 or 300 millionanimals to 100 million could recover."It will give us some breathing space,"he adds. Others say that only ifthe Australian government supportsadditional rabbit control measures,such as fumigating and ripping upburrows, while populations are attheir most vulnerable, can this menacebe contained.