Flu is respiratory infection caused by viruses and it is differ from common cold. There are three types of flu: seasonal flu, pandemic, and avian (bird), swine flu. Seasonal Flu occurs yearly in the late fall and winter. It affects between 5 to 20 percent of population each flu season. Pandemic Flu is spread easily form person to person. It is virulent strains that create world-wide epidemic. Avian (bird) flu virus occurs in wild birds and is rarely spread to humans. However, viruses can jump over spices barriers and spread disease to domesticated birds and then pigs. From there viruses can be passed to humans. In 1997, scientists discovered that influenza skipped pigs step and affected humans directly from birds. It caused number of deaths is Asia. If this type of flu could be transmitted between humans, a new epidemic (pandemic) will occur.
http:///topics/Flu/understandingFlu/definitionsOverview.htmwww3.niaid.nih.gov
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