Molecular characterization of H5N2 avian influenza viruses isolated from South African ostriches in 2006.

Highly pathogenic avian influenza (HPAI) H5N2 reemerged in ostriches in South Africa during 2006, and a low-pathogenic AI H5N2 virus was also isolated. Molecular and phylogenetic characterization was performed to determine whether the outbreak strains were genetically derived from the supposedly eradicated Eastern Cape ostrich outbreak HPAI H5N2 strain of 2004. It was demonstrated that although the 2004 and 2006 South African H5N2 strains shared a common ancestor, the two outbreaks were not related. Not only were extensive reassortments with wild bird viruses involved in the evolution of the 2006 strains, but the precursor HA molecule HA0 cleavage site sequence of the 2006 HPAI H5N2 virus also contained fewer basic amino-acid insertions. Multiple transmission events occurred from wild birds to ostriches in 2006, and it appears that a reservoir of H5N2 with pathogenic potential for poultry is established in the South African wild duck population.