May 28, 2013 — A novel disease in songbirds has rapidly evolved to become more harmful to its host on at least two separate occasions in just two decades, according to a new study. The research provides a real-life model to help understand how diseases that threaten humans can be expected to change in virulence as they emerge.
"Everybody who’s had the flu has probably wondered at some point, 'Why do I feel so bad?'" said Dana Hawley of Virginia Tech, the lead author of the study to be published in PLOS Biology on May 28, 2013. "That’s what we’re studying: Why do pathogens cause harm to the very hosts they depend on? And why are some life-threatening, while others only give you the sniffles?"
Disease virulence is something of a paradox. In order to spread, viruses and bacteria have to reproduce in great numbers. But as their numbers increase inside a host’s body, the host gets more and more ill. So a highly virulent disease runs the risk of killing or debilitating its hosts before they get a chance to pass the bug along. It finds the right balance through evolution, and the new study shows it can happen in just a few years.
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