A plague on the pest – rabbit calicivirus disease and biological control

Activity 4

Learning from the myxomatosis experiment

When the myxoma virus was released in Australia in 1950 it was estimated that in some places 90 per cent of the rabbits died within 3 or 4 weeks.

  1. Explain why, almost 50 years later, we still have a rabbit problem.
  2. What could be done to prevent the same thing happening with the calicivirus?

Teachers notes

  1. There is still a rabbit problem in Australia because the effectiveness of the myxoma virus decreased. There are two main reasons for this: the ability of the virus to kill rabbits decreased and the proportion of resistant rabbits increased. (See Box 1, The use of the myxoma virus to control rabbit numbers.) In addition, the impact of the myxoma virus in Central Australia was reduced because there were few flies or mosquitoes there to help spread the virus.

  2. After the introduction of the calicivirus, farmers should reduce the number of surviving rabbits by using other methods to kill the survivors (eg, poison baits, shooting, ripping up warrens). The eradication is more effective when farmers coordinate their efforts with their neighbours.

The effectiveness of calicivirus as an effective biological control agent could be prolonged by correctly timing releases. Factors to be considered are:

  • the virus can be spread by rabbit-rabbit contact (high rabbit numbers enhance this method of transmission);

  • cool, moist conditions are ideal for the survival of the virus and possibly for the survival of vectors;

  • if rabbit kittens under about 8 weeks old are infected by the virus and develop a life-long immunity to it.

To date, the best spread of the virus and most effective killing of the rabbits have been recorded during the breeding season of rabbits.

This question could lead to an interesting discussion about whether every last rabbit has to be killed in order to wipe out rabbits in Australia and, if this happens, whether we can then stop being vigilant about possible new outbreaks. At this stage it appears that the rabbit will remain in Australia for some time.

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Posted February 1997.