The 2009 Swine Flu pandemic is caused by a novel reasserted H1N1 subtype of H1N1 influenza A virus that had not been recognized previously in swine or humans. This newly emerged strain represents a quadruple reassortment of two swine strains, one human strain, and one avian strain of influenza. The largest proportion of genes comes from swine influenza viruses (30.6% from North American swine influenza strains, 17.5% from Eurasian swine influenza strains), followed by North American avian influenza strains (34.4%) and human influenza strains (17.5%). Influenza A virus is a member of family Orthomyxoviridae. Based on the antigenicity, virus may be classified into 17 Hemagglutinin (H1-H16) and 10 Neuraminidase (N1-N9) subtypes. Influenza A virus genome is composed of eight segments of single-stranded, negative-sense RNA and each of which encodes ten proteins.