Influenza A virus subtype H5N1 is a subtype of the Influenza A virus. Subtype H5N1 is commonly known as avian influenza or bird flu. H5N1 may cause more than one influenza pandemicas it is expected to continue mutating in birds. The dominant strain of HPAI A （H5N1） evolved creating the Z genotype. It has also been called Asian lineage HPAI/A/H5N1 which is divided into 2 antigenic clades. "Clade 1 includes human and bird isolates from Vietnam， Thailand， and Cambodia and bird isolates from Laosand Malaysia. Clade 2 viruses were first identified in bird isolates from China， Indonesia， Japan， and South Korea before spreading westward to the Middle East， Europe， and Africa.
