A Hare-brained Scheme
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A. Despite many efforts to control them, rabbits have overrun Australia and are causing blight, erosion and extinction wherever they go. On an island off the Australian coast, scientists had been testing a deadly rabbit virus to see whether it could serve as a weapon against the long-eared pests. The virus escaped from the island and is now spreading, uncontrolled, through the Australian outback. The unplanned viral outbreak — together with another experiment involving pollen — raises concerns about the ability of scientists to control the spread of organisms that they introduce into the environment.
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B. The offending bug causes rabbit calicivirus disease (RCD). First identified in China in 1984, the virus surfaced in Europe in 1986. The only animals affected by the virus are European rabbits, Oryctolagus cuniculus, which usually die within two days of contracting the disease. Australians and New Zealanders soon noticed RCD’s potential as an anti-rabbit agent, and the Australia and New Zealand .Rabbit Calicivirus Disease Program was born. Funded by the Commonwealth Science and Industry Research Organization (CSIRO), among other agencies, the programme set up a test site at Wardang Island off the coast of South Australia to evaluate the disease for an eventual release, probably in 1997.
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C. Officials foresaw little possibility of the virus's escaping from the island, but escape it did. In October, CSIRO announced that RCD had spread beyond the quarantine area despite "strict surveillance" and “comprehensive micro security measures". Within a week a rabbit had died of RCD at Point Pearce on Yorke Peninsula near the island. Scientists speculate that bush flies may have transmitted the virus to the mainland.
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D. A frantic attempt to contain the virus followed. Scientists were stunned when the virus appeared at Yunta, 260 kilometres from Point Pearce, and then at Blinman, another 200 kilometres away. Officials suspect that humans may have been responsible for the disease’s spread. A reporter for the Sydney Morning Herald may have unintentionally carried the virus from Point Pearce to Yunta; farmers, whose animosity toward rabbits runs deep, may also be helping the virus along, possibly by releasing infected animals.
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E. By the end of October, officials gave up trying to control the spread of RCD and instead concentrated on measuring the disease’s effect. The virus spread rapidly, reaching Broken Hill in New South Wales by early December. “In broad terms, where the virus has been present for four to five weeks, there is over a 95 per cent kill rate,” said Niall Byrne of CSIRO. This is enough to reduce the population, despite rabbits’ legendary fecundity.
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F. Rough estimates put the current rabbit population at 200 to 300 million. At these numbers, they can devastate the flora of the countryside and drive other plant-eaters into starvation. “The scale of rabbit damage is just vast," Byrne says. “Twenty-five per cent of native mammals in New South Wales have been rendered locally extinct, and the major factor is rabbits."
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G. RCD is not the first anti-rabbit virus released in Australia. In 1950, myxomatosis was introduced, and the initial success was astounding. A premyxomatosis rabbit population of about 600 million crashed to about 50 million. But the virus failed to control the rabbit population for long, because a co-evolution between the virus and rabbits followed. According to Edward M. Berger, a biologist at Dartmouth College, “a less virulent strain of virus evolved, and the (rabbit) survivors became more resistant,” enabling both the virus and the host to survive.
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H. RCD is not the only organism that is difficult to control. A recent Scottish study shows that a previously used pollen dispersion model — which would probably have been used to predict how fast genes from a transgenic crop leak into the environment — badly underestimated the amount of pollen that spreads from large oilseed rape fields.
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I. The study’s authors discovered that pollen can disperse much farther than the model predicts; pollen levels that had been expected no more than 100 metres away were observed at distances up to 2.5 kilometres. The study thus demonstrates the principle that any genes that scientists introduce into a crop can quickly spread into wild populations. A herbicide-resistant strain might cause “superweeds” that would be difficult to contain. This incident, like the one in Australia, should serve as a warning; it is easy to release an organism into a new environment but hard to control its spread.