Highly pathogenic avian influenza (HPAI) caused by the H5N1 strain was first reported in Southeast Asia in late 2003, although the H5N1 virus is now considered to have emerged as early as 1996 when it was first identified in geese in Guangdong Province in southern China. Since then, HPAI has spread rapidly and over large distances with outbreaks occurring in domesticated poultry and some wild bird populations in Mongolia, southern Russia, the Middle East and, in 2005, in Europe and Africa.