1. Introduction Influenza A viruses belong to the family Orthomyxoviridae withthe majority of viruses maintained in wild aquatic bird reservoirs,predominantly those of the anseriform species. Classification ofthese viruses is determined by the two surface glycoproteins, thehemagglutinin (HA) and neuraminidase (NA) of which 16 HA and9 NA subtypes have been isolated from aquatic birds (Kim et al.,2009). The migratory nature of the aquatic fowl reservoir resultsin the wide geographic spread and distribution of most circulat-ing subtypes. A consequence of this geographic distribution inmigratory birds is the is the potential contact of infected bird withdomestic avian and mammalian species, including humans, withnovel influenza A subtypes that can cross the host range barrierand initiate local epidemics or widespread influenza pandemics(Webster et al., 1992).Since their detection in Asia in 1996, the highly pathogenic avianinfluenza (HPAI) H5N1 viruses have spread to many countries in theeastern hemisphere becoming endemic in populations of domes-tic birds in a more restricted number of countries and transientlyinfecting a number of other hosts along the way. The mechanism ofvirus spread throughout the hemisphere is not entirely clear, butprobably as a result of both wild birds and poultry trade. While wild