Rabbit redux.

Rabbit Redux 

Britain's rabbit population is expected to balloon again as the effects of the once deadly viral myxomatosis grow steadily less severe. In the early 1950s the rabbits had become a major threat to agriculture and forestry, and so the virus--originally used effectively in Australia, where rabbits are not native--was spread among them to reduce the rodents to manageable proportions. It's the old story of an animal growing resistant to control measures through natural selection: the rabbits' resistance to infection has outdistanced increases in artificial strengthening of the virus. The population of these creatures in Britain has now risen again to the level it was at in 1953, the year the virus was first introduced. John Ross, of the Ministry of Agriculture's Fisheries and Food Laboratory, says that myxomatosis is killing one rabbit out of three at present in Britain, but "that's nothing like enough--one doe can produce 25 to thirty young in one season. In order to keep the population steady, 90 per cent of rabbits would have to be killed before the following breeding season.' A solution may be found in Australian experiments to alter the virus genetically to make it much more potent. One way to do this would be to insert genes into the virus that would suppress rabbit fertility and decrease reproduction. Another is to introduce a bacterial toxin into the genetic blueprint of the virus that would cause the death of infected rabbits. Practical application of these experiments is liable to be several years away, however.