A 945 nucleotide region (bases 76–1020) of the HA1 part of the HA gene was obtained for 31 influenza viruses of H7 subtype
isolated primarily from Europe, Asia and Australia over the last 20 years. These were analysed phylogenetically and compared
with sequences of the same region from 23 H7 subtype viruses available in Genbank. The overall results showed two geographically
distinct lineages of North American and Eurasian viruses with major sublineages of Australian, historical European and equine
viruses. Genetically related sublineages and clades within these major groups appeared to reflect geographical and temporal
parameters rather than being defined by host avian species. Viruses of high and low virulence shared the same phylogenetic
branches, supporting the theory that virulent viruses are not maintained as a separate entity in waterfowl.
Received October 25, 1999/Accepted November 18, 1999