Bulach, D., Halpin, R., Spiro, D., Pomeroy, L., Janies, D., Boyle, D. B.
Molecular Analysis of H7 Avian Influenza Viruses from Australia and New Zealand: Genetic Diversity and Relationships - 1976 to 2007
J Virol. 2010 Jul 28; 84(19): 9957-66.
Full genome sequencing of 11 Australian and one New Zealand subtype H7 avian influenza A isolates has enabled the comparison of sequences from each of the genome segments to other subtype H7 avian influenza A. The inference of phylogenetic relationships for each segment has been used to develop a model of the natural history of these viruses in Australia. Phylogenetic analysis of the hemagglutinin segment indicates that the Australian H7 isolates form a monophyletic clade. This pattern is consistent with the long-term, independent evolution that is, in this instance, associated with geographic regions. Based on the analysis of the other H7 hemagglutinin sequences, three other geographic regions for which similar monophyletic clades have been observed were confirmed. These regions are Eurasia plus Africa, North America, and South America. Analysis of neuraminidase from H7N1, H7N3 or H7N7 genomes revealed the same region based relationships. This pattern of independent evolution of Australian isolates is supported by analysis of each of the six remaining genomic segments. These results in conjunction with the occurrence of five different combinations of neuraminidase subtypes (H7N2, H7N3, H7N4, H7N6, H7N7) among the 11 Australian isolates suggest the maintenance host(s) are nearly exclusively associated with Australia. The single lineage of Australian H7 hemagglutinin sequences despite the occurrence of multiple neuraminidase types suggests a genetic pool from which a variety of reassortants arise rather than the presence of a small number of stable viral clones. This pattern of evolution is likely to occur in each of the regions mentioned above.