Influenza A viruses infect a wide range of hosts, including many avian species, and various mammalian species, such as swine, ferrets, felids, mink, whales, horses, seals, dogs, civets, and humans [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] . Wild birds (ducks, geese, swans, and shorebirds) are important natural reservoirs of these viruses, and all of the known 16 HA and 9 NA subtypes have been found in these birds [32] [33] [34] [35] . In most cases, these subtypes are found within the gastrointestinal tract of the birds, are shed in their feces, and rarely cause disease [32] . Since 2002, however, HPAI H5N1 viruses originating in Asia have been reported from approximately 960 wild bird species, causing disease in some instances and asymptomatic shedding in others [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] . The virus has now spread across Asia, Europe, the Middle East, and some African countries. Additional species, such as tigers, leopards, cats, stone martens, and humans have also become infected with HPAI H5N1 [49] . This spread of H5N1 into a wide range of animal and avian species may enhance the spread of the virus into the human population as it interacts with animals in a number of ways (increased land use, markets, consumption) [44] . Thus, the potential contact, transmission, and mutability of HPAI H5N1 worldwide will increase as the number of species and their interactions increase, complicating prevention, surveillance and treatment possibilities.