When humans weaponized a virus to cull rabbits, nature fought back with evolution.
In short: In the 1950s, scientists released the myxoma virus in Australia, France, and Chile to eradicate wild European rabbit populations. It was a biological control experiment that worked too well, then backfired. As rabbits developed resistance, the virus evolved to become less lethal, creating a complex, ongoing arms race.
The myxoma virus is a poxvirus naturally occurring in South American tapeti and North American brush rabbits, where it causes only mild skin nodules. However, when introduced to the European rabbit—a species with no natural immunity—it triggers myxomatosis, a severe, often fatal disease. The virus is primarily spread by biting arthropods like mosquitoes and rabbit fleas, though it can also travel via direct contact or contaminated objects like water bottles and feeders.
The initial release of the virus was devastating. In 1952, a private estate owner in France introduced the Lausanne strain, which subsequently swept across Western Europe, reducing wild rabbit populations by up to 99% in the United Kingdom and 95% in Spain. This collapse had cascading ecological consequences, pushing specialized predators like the Iberian lynx and Spanish imperial eagle toward extinction. In Australia, where the virus was released in 1950, it initially achieved a 99.8% fatality rate.
The long-term outcome, however, was not total eradication but a classic example of host-pathogen coevolution. Natural selection favored rabbits that were more resistant to the virus and viral strains that were less virulent. Attenuated strains allowed infected rabbits to survive longer, which paradoxically enhanced the virus's ability to spread. Today, the relationship remains complex and unpredictable; while current strains in Australia are less lethal than the original, they still exert significant control over feral populations. This ongoing adaptation demonstrates how quickly both host and pathogen can shift under intense selective pressure.
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- Summary by Intellect · source: Myxomatosis
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