There are basically three types of influenza viruses i.e. A, B and C. Influenza A viruses are further classified, based on the viral surface proteins (H) and neuraminidase (N). Sixteen H subtypes (or serotypes) and nine N subtypes of influenza A virus have been identified. The type A viruses are the most virulent human pathogens among the three influenza types and cause the most severe disease. The type B and C viruses are less common than type A.
What is ‘Swine Flu” then? Influenza A H1N1 caused “Spanish Flu” in 1918, “Swine flu” in 2009; H2N2 caused “Asian Flu”; H3N2 caused “Hong Kong Flu”; H5N1 caused “bird flu”.
The Pandemic H1N1/09 virus is believed to be a new strain of Influenza A virus subtype H1N1 responsible for the 2009 flu pandemic. In the 2009 flu pandemic, the virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses
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