Influenza viruses belong to the family Orthomyxoviridae and are classified into three types, A, B and C based on the identity of major internal protein antigens (6) . Influenza A and C viruses can infect multiple mammalian species, while influenza B virus is almost exclusively a human pathogen (7) . Influenza A viruses cause the greatest morbidity and mortality in humans. Interestingly, the largest pool of influenza A viruses is maintained by horizontal spread in wild aquatic birds, in which the virus does not normally cause any disease (6, 8) . Food and companion animal populations such as poultry, swine, horses and dogs support sustained replication of certain lineages of influenza A, with minimal to lethal disease depending on the virulence of the strain (6) . Influenza viruses have evolved in association with their various hosts in different continents for extended periods of time (9) . This co-evolution has resulted in extensive genetic divergence among the extant viruses currently available for analysis.