Bird-carried pathogens are above all susceptible to being spread worldwide because of human activities such as legal or illegal trade of wild and domestic birds or bird products (28) . The mechanism for the introduction of WNV into America in 1999 is not known with certainty, but a plausible scenario is the importation of an infected bird (29, 30) . Similarly, the highly pathogenic AI strain H5N1 was isolated in Belgium from crested hawk-eagles (Spizaetus nipalensis) smuggled by air travel (31) . In Asia, transmission of H5N1 influenza virus has mainly been the result of human activity such as live-poultry markets and the international trade of birds, bird products, or contaminated equipment (32) (33) (34) (35) .