Avian Influenza (Bird Flu)
An influenza pandemic is a global outbreak of disease that occurs when a new influenza A virus appears or "emerges" in the human population, causes serious illness, and then spreads easily from person to person worldwide. Pandemics are different from seasonal outbreaks or "epidemics" of influenza. Seasonal outbreaks are caused by subtypes of influenza viruses that are already in existence among people, whereas pandemic outbreaks are caused by new subtypes or by subtypes that have never circulated among people or that have not circulated among people for a long time. Past influenza pandemics have led to high levels of illness, death, social disruption, and economic loss. There are many different subtypes of Influenza or "flu" viruses. The subtypes differ based upon certain proteins on the surface of the virus (the hemagglutinin or "HA" protein and the neuraminidase or the "NA" protein). Pandemic viruses appear (or "emerge") as a result of a process called "antigenic shift," which causes an abrupt or sudden, major change in influenza A viruses. These changes are caused by new combinations of the HA and/or NA proteins on the surface of the virus. This change results in a new influenza A virus subtype. The appearance of a new influenza A virus subtype is the first step toward a pandemic, but the new virus subtype also must spread easily from person to person to cause a pandemic. Once a new pandemic influenza virus emerges and spreads, it normally becomes established among people and moves around or "circulates" for many years as seasonal epidemics of influenza. The U.S. Centers for Disease Control and Prevention and the World Health Organization have large surveillance programs to monitor and "detect" influenza activity around the world, including the emergence of possible pandemic strains of influenza virus. (The Washington Times A21) There are growing fears of an influenza pandemic as avian flu sweeps through poultry stocks across Asia....
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