Pandemic Influenza:a time-honored disease and a great calamity to human

In the passing three hundred years,no less than 10 times influenza pandemic have been recorded. Due to its periodicity , unpredictability,calamity and durability, we the human have not had ways to accurately predict as well as effectively avoid a start of pandemic yet. Since December 2003, highly pathogenic H5N1 avian influenza virus has swept through poultry populations across Asia and parts of Europe. The outbreaks are historically unprecedented in scale and geographical spread. It has established an ecological niche in poultry, making it extremely difficult to control outbreaks. Outbreaks have recurred despite aggressive control measures.Evidence shows that the H5N1 virus is most likely endemic in many parts of Asia.Meanwhile,the virus continues to evolve(including expanded host ranges, increased pathogensis and stability ) and to cause human infections with high mortality.For these reasons, the current outbreaks of influenza A(H5N1) in poultry and humans in Asia, has moved the world closer to a pandemic than any time since 1968, when the last such event occurred.