BIO220H1 Lecture Notes - Lecture 20: Myxoma Virus, Rabbit Haemorrhagic Disease, Frank Fenner
The Next Chapter in a Viral Arms Race
In 1898, scientists in Uruguay noticed that some of their laboratory rabbits were
dying from a mysterious illness, their skin riddled with tumors and weeping
wounds. The researchers named the disease myxomatosis.
myxomatosis is caused by myxoma virus—>highly lethal, specific to rabbits, and
spread by mosquito bites
government of Australia finally released myxoma-infected rabbits into rabbit
population. virus killed millions of rabbits.
!
The myxoma virus quickly evolved. The strain that had initially been used was
almost inescapably lethal, killing virtually every rabbit it infected. But virologist
Frank Fenner discovered that, within a few years, this strain had been replaced
with milder ones, which killed less rapidly and frequently.
how viruses evolve in the wild?
They’ve also permeated into the popular consciousness, creating an intuitive
sense that lethal viruses eventually evolve into milder forms, which are less likely
to completely wipe out their hosts. But “the notion that everything’s heading
toward a state of long-term co-existence and happiness is not always the case,”
says Andrew Read,“There are plenty of examples where the virus has got nastier
over time.”
And as it happens, myxoma is one such example. “It went from exceptionally
nasty to just nasty, and now has turned round and cranked up the nastiness
again,” Read says.
The virus was never entirely harmless. After its release in 1950, it went from
killing more than 99 percent of rabbits to killing around 75 percent of them, or
under 50 percent in some cases. In response, the rabbits evolved resistance. And
that relaunched the arms race between myxoma and rabbits, prompting the virus
to evolve its own countermeasures, which it still deploys today.
!
Read and colleagues compared 1950 virus strain with 1990 strain (this was tried
on lab rabbit not wild rabbits)—> virus had gained a new ability: It could
completely shut down a rabbit’s immune system. This stops the
animals from effectively clearing the virus.
Inadvertently, it also means the bacteria that normally live peacefully in the
rabbits’ bodies run amok, spreading through their internal organs and causing
septic shock. These rabbits never develop the skin tumors or any of the classic
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The next chapter in a viral arms race. In 1898, scientists in uruguay noticed that some of their laboratory rabbits were dying from a mysterious illness, their skin riddled with tumors and weeping wounds. The researchers named the disease myxomatosis. myxomatosis is caused by myxoma virus >highly lethal, specific to rabbits, and spread by mosquito bites government of australia finally released myxoma-infected rabbits into rabbit population. virus killed millions of rabbits. The strain that had initially been used was almost inescapably lethal, killing virtually every rabbit it infected. They"ve also permeated into the popular consciousness, creating an intuitive sense that lethal viruses eventually evolve into milder forms, which are less likely to completely wipe out their hosts. But the notion that everything"s heading toward a state of long-term co-existence and happiness is not always the case, says andrew read, there are plenty of examples where the virus has got nastier over time.
