During the past several years, an especially virulent strain of avian flu, designated H5N1, has ravaged flocks of domesticated poultry in Asia and spread to migratory birds and (rarely) to humans. Now found from Russia and Japan to Indonesia, it is moving inexorably toward Europe. Since 2003, more than 60 human deaths have been attributed to H5N1. Public health experts and virologists are concerned about the potential of this strain because it already has two of the three characteristics needed to cause a pandemic: It can jump from birds to human, and can produce a severe and often fatal illness. If additional genetic evolution makes H5N1 highly transmissible among humans -- the third characteristic of a pandemic strain -- a devastating world-wide outbreak could become a reality.As I said in the comments below, if you want to keep in touch with the evidence as it appears, here's three such sources of evidence that wil be worth keeping an eye on:
Moreover, this is an extraordinarily deadly variant: The mortality rate for persons infected with the existing H5N1 appears to be around 50 percent, whereas the usual annual flu bug kills fewer than one percent.
CIDRAP (the Center for Infectious Disease Research & Policy), the Avian Flu blog maintained by academics at George Mason University, and the collaborative reference site Flu Wiki.