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Discovery

Rabbit Calicivirus Disease

Rabbits and how to control them effectively has been an important and frustrating issue for farmers and environmentalists for many years now. Left uncontrolled the population increases exponentially -- leaving a trail of devastated vegetation in its wake. There have been many previous attempts to control this growth in New Zealand, the most controversial being the myxomatosis virus. Now, New Zealand has another choice in the fight against the rabbit -- Rabbit Calicivirus Disease (RCD).

Calicivirus, which has been found in Europe and China since 1984, causes blood clots to form in the major organs. This blocks blood vessels and ultimately causes death within two days, eliminating the inhumane quality of myxomatosis which prevented it from being introduced to New Zealand. Formerly known as Rabbit Haemorrhagic Disease, RCD has been proven by field tests to be highly effective, but also highly uncontrollable and unpredictable. The disease, which was undergoing field tests on a high security quarantine facility at Wardang Island off the coast of South Australia, managed to escape and infect animals on the mainland, causing the virus to spread rapidly throughout many parts of Australia.

The speed with which the virus spread was another factor which puzzled scientists. When the disease originated in Europe, the spread of the disease was comparatively slow. With the Australian outbreak, the disease spread at a rate which at one time exceeded eight kilometres per day, suggesting to scientists that there was a vector in the transmission which was not present in earlier outbreaks.

Speculation among many scientists, according to John Auty, Education Officer at AgResearch Wallaceville, is that the Australian bushfly, which feeds off the protein around the eyes of rabbits, as well as other animals, is acting as a vector of transmission. This also offers an answer as to how the virus escaped from Wardang Island, as due to environmental conditions there was an influx of the flies throughout South Australia at the time of the virus' escape.

Any New Zealand outbreak of RCD would differ immensely from that which was seen in Australia. The Australian Bushfly is not present in New Zealand, and therefore transmission of the virus would possibly not be as speedy as what was observed in Australia. Dr Peter Kettle, Director of Science Policy for the Ministry of Agriculture, said in an interview with Kim Hill that it was "unlikely it [the virus] will go through the country like a wildfire". This is partially because in New Zealand we have a large number of discrete rabbit populations, with little contact between the different groups, whereas in Australia the population is in one continuous population, allowing the virus to be spread rapidly from animal to animal. This is strongly supportive of RCD's introduction to New Zealand, offering the possibility of controlling the spread of the virus within different parts of New Zealand effectively.

There is, by no means, a definite move to introduce RCD to New Zealand. Other aspects also have to be considered, not the least of which being the effect of the virus on native animals. Although the virus at this stage seems to be host specific, and is not known to affect any animal other than rabbits, it is possible, as with any other virus, that it could mutate and affect other species.

Australian academics Glen Albrecht and Stuart Pearson expressed alarm at the possibility of the virus changing into a form where humans could become infected, and countless scientists have warned at the unpredictability of viruses and the ease with which it could mutate. Some US scientists even speculate that it can cross the species barrier without difficulty, creating another problem for those in favour of introducing RCD.

But becoming infected with the virus itself is not the only problem for native animals. When rabbits are removed from the food chain, their current predators -- animals such as stoats and cats -- will have to look to other animals to replenish the gap left by the rabbits. Possible victims? -- Black Stilts, Giant Skinks, and especially ground dwelling birds, such as the Kiwi, many of which are endangered.

All in all, many factors will need to be considered by scientists before any introduction of RCD to New Zealand can take place, with the environmental and ecological consequences needing extensive weighting. Unfortunately, as the virus can apparently survive on clothing (in ideal conditions) for in excess of a month, nothing can be done to stop an accidental, or unprepared, introduction of RCD into New Zealand.

This is the winning entry in the NZSM's Science Journalism Competition.

Malcolm Birdling is a fifth form student at Heretaunga College, in Upper Hutt. He is interested in chemistry and biology, and hopes to become a medical doctor or a medical researcher.