Australia. The myxovirus, which afflicts and exterminates rabbits, is intentionally introduced in the hope of controlling the non-native species, which is in turn severely altering the local flora and fauna. The first year, it rewards Australians with a 99.8% mortality rate, but then in the second year the mortality rate drops to 90% and then plummets to 25% in the third year, dashing hopes of significantly reducing the rabbit population. The problem is that the myxovirus has pursued its own interests (unfortunately different from ours) and, through Darwinian evolution, has mutated to kill fewer rabbits (be less lethal), thus giving the infected rabbit time to spread to other rabbits.
