Thank you for your letter dated 28th February 1996 concerning the use of genetically altered viruses in Australia. I have consulted a number of my colleagues with more experience than I have in this area. They have made the following comments based on the information contained in the articles submitted with your letter:

• The release of exotic viruses has unpredictable consequences. The relevance of vectors which may induce sterility, if effective, would appear to be more safe. However, this carries the risk of disturbing existing ecological balance.

• Viruses and rabbits (and cane toads) are all capable of genetic mutations and great diversity. The likely outcome for release of calicivirus will be calicivirus resistant rabbits and attenuated caliciviruses.

• These viruses will cause a dramatic (80-90%) drop in numbers in the short term, but things will return to 'normal' in a matter of a few years.The new generations will be resistant to the virus. The whole strategy is fallacious unless it is combined with the introduction of a new predator to redress the equilibrium.This is itself very unpredictable.The sterility inducing vaccines are a much better solution because the affected animals continue to compete for resources over a prolonged period. However, in the absence of a predator, things will get out of hand eventually. Release of exotic pathogens is an inherently risky undertaking.