Pandemics in the news

I have a morbid fascination with pandemics -- we have had them before and there are more lurking on the fringes of society. The biological evolution is also fascinating to me -- too effective and you kill the host before it has a chance to infect other potential hosts. Too weak and it is more difficult to infect. Meet House Finch eye disease - from Phys.org:

Diseases can rapidly evolve to become more�or less�virulent, according to songbird study
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.

Hawley and her coauthors studied House Finch eye disease, a form of conjunctivitis, or pinkeye, caused by the bacteria Mycoplasma gallisepticum. It first appeared around Washington, D.C., in the 1990s. The House Finch is native to the Southwest but has spread to towns and backyards across North America. The bacteria is not harmful to humans, which makes it a good model for studying the evolution of dangerous diseases such as SARS, Ebola, and avian flu.

"There's an expectation that a very virulent disease like this one will become milder over time, to improve its ability to spread. Otherwise, it just kills the host and that's the end of it for the organism," said Andr� Dhondt, director of Bird Population Studies at the Cornell Lab of Ornithology and a coauthor of the study. "House Finch eye disease gave us an opportunity to test this�and we were surprised to see it actually become worse rather than milder."

Interesting stuff...