Here's a sobering thought: Wild birds — including city pigeons and ubiquitous Canada geese — carry 170 different types of bird flu. You know, all those viruses with the Hs and Ns in their names, like H1N1 and H5N1.
Only a dozen of these viruses have infected humans so far, but many of those have been deadly, and three of them have caused global flu pandemics.
Does every bird flu that leaps into people have the potential to turn into the next "big one" that spreads rapidly around the world?
Scientists have completed the first assessments of how readily the H7N9 flu virus in China can pass among ferrets and pigs. The mammals provide the best inkling of how dangerous these bugs may become for humans.
The news is both bad and good. They've found the new bird virus is easily passed between ferrets sharing the same cage.