It's believed that the bird flu virus is carried and spread by migratory birds as well as via the trading of live poultry. Improved surveillance as well as enhanced farm and market bio-security measures have been put in place. Vaccine research and production has also been stepped up. Yet, no one can rule out a possible outbreak among humans.

Lance Jennings said, "We will have an human influenza epidemic. We don't know when and we don't know how severe it is. The current avian influenza situation, circulation of H5N1 strain virus globally is of real concern."

What concerns public health experts is the possibility that the H5N1 virus may mutate into a new kind of virus that is easily transmitted from human to human. Fortunately, this has not happened today. Yet, the threat is real.

Editor:Du Xiaodan