Abstract:
Low-pathogenicity (LPAI) and high-pathogenicity (HPAI) avian influenza viruses are periodically isolated from
South African ostriches, but during 2002 the first recorded outbreak of LPAI (H6N2) in South African chickens occurred on
commercial farms in the Camperdown area of KwaZulu/Natal (KZN) Province. Sequence analysis of all eight genes were
performed and phylogenetic analysis was done based on the hemagglutinin and neuraminidasc sequences. Results from
phylogenetic analyses indicated that the H6N2 chicken viruses most likely arose from a reassortment between two South African
LPAI ostrich isolates: an H9N2 virus isolated in 1995 and an H6N8 virus isolated in 1998. Two cocirculating sublineages of H6N2
viruses were detected, both sharing a recent common ancestor. One of these sublineages was restricted to the KZN province. The
neuraminidase gene contained a 22–amino acid deletion in the NA-stalk region, which is associated with adaptation to growth in
chickens, whereas the other group, although lacking the NA-stalk deletion, spread to commercial farms in other provinces. The
persistence of particular H6N2 types in some regions for at least 2 yr supports reports from Asia and southern California suggesting
that H6N2 viruses can form stable lineages in chickens. It is probable that the ostrich H6N8 and H9N2 progenitors of the chicken
H6N2 viruses were introduced to ostriches by wild birds. Ostriches, in which AI infections are often subclinical, may serve as mixing vessels for LPAI strains that occasionally spill over into other poultry.
