Think All Viruses Get Milder With Time? Not This Rabbit-Killer

The myxoma virus, fatal to millions of Australian Rabbit-Killer, is a textbook example of the unexpected twists in the evolution of viruses and their hosts

Think All Viruses Get Milder With Time Not This Rabbit-Killer

As the Covid death rate worldwide has fallen to its lowest level since the early weeks of the pandemic in 2020, it may be tempting to conclude that the coronavirus is becoming irreversibly milder. That notion fits with a widespread belief that all viruses start off nasty and inevitably evolve to become gentler over time.“There’s been this dominant narrative that natural forces are going to solve this pandemic for us,” said Aris Katzourakis, an evolutionary biologist at the University of Oxford.

But there is no such natural law. A virus’s evolution often takes unexpected twists and turns. For many virologists, the best example of this unpredictability is a pathogen that has been ravaging rabbits in Australia for the past 72 years: the myxoma virus.Myxoma has killed hundreds of millions of rabbits, making it the most deadly vertebrate virus known to science, said Andrew Read, an evolutionary biologist at Pennsylvania State University. “It’s absolutely the biggest carnage of any vertebrate disease,” he said.

After its introduction in 1950, myxoma virus became less lethal to the Rabbit-Killer, but Dr. Read and his colleagues discovered that it reversed course in the 1990s. And the researchers’ latest study, released this month, found that the virus appeared to be evolving to spread even more quickly from rabbit to rabbit. Scientists intentionally introduced the myxoma virus to Australia in the hopes of wiping out the country’s invasive rabbit population. In 1859, a farmer named Thomas Austin imported two dozen rabbits from England so he could hunt them on his farm in Victoria. Without natural predators or pathogens to hold them back, they multiplied by the millions, eating enough vegetation to threaten native wildlife and sheep ranches across the continent.

In the early 1900s, researchers in Brazil offered Australia a solution. They had discovered the myxoma virus in a species of cottontail Rabbit-Killer native to South America. The virus, spread by mosquitoes and fleas, caused little harm to the animals. But when the scientists infected European rabbits in their laboratory, the myxoma virus proved astonishingly lethal The rabbits developed skin nodules packed with viruses. Then the infection spread to other organs, usually killing the animals in a matter of days. This gruesome disease came to be known as myxomatosis.

The Brazilian scientists shipped samples of the myxoma virus to Australia, where scientists spent years testing it in labs to make sure it posed a threat only to rabbits and not other species. A few scientists even injected myxoma viruses into themselves. After the virus proved safe, researchers sprayed it into a few warrens to see what would happen. The rabbits swiftly died, but not before mosquitoes bit them and spread the virus to others. Soon, rabbits hundreds of miles away were dying as well.

Source: This news is originally published by nytimes