When a pathogen jumps species, it is often highly lethal in its new host. But a quick kill does not make for continued transmission; the host must survive long enough to pass the pathogen on to additional victims. Thus, under natural conditions, a newly emergent, highly lethal pathogen that kills very rapidly is expected to evolve lower virulence. At the same time, however, the host species is evolving resistance to the infection, which then provides an environment for increasing pathogen virulence. Could humans be creating a similar environment by vaccinating or breeding our farm animals to resist disease?
Wild rabbit populations in Australia declined dramatically in the early 1950s after the release of the myxoma virus, which caused a fatal disease called myxomatosis. Slowly, the populations started to rebound, though they never fully recovered.
To track the myxoma virus (MYXV) as it devastated the invasive rabbit populations of Australia, researchers conducted what are known as common garden experiments, testing the effects of the evolving viral strains on laboratory rabbits, as well as the effects of a standard virus on different samples of rabbits in the wild over time.
