Objective: To determine the extent of genetic variation among internationally collected HIV-1 isolates, to analyse phylogenetic relationships and the geographic distribution of different variants.
Design: Phylogenetic comparison of 70 HIV-1 isolates collected in 15 countries on four continents.
Methods: To sequence the complete gag genome of HIV-1 isolates, build multiple sequence alignments and construct phylogenetic trees using distance matrix methods and maximum parsimony algorithms.
Results: Phylogenetic tree analysis identified seven distinct genotypes. The seven genotypes were evident by both distance matrix methods and maximum parsimony analysis, and were strongly supported by bootstrap resampling of the data. The intra-genotypic gag distances averaged 7%, whereas the inter-genotypic distances averaged 14%. The geographic distribution of variants was complex. Some genotypes have apparently migrated to several continents and many areas harbor a mixture of genotypes. Related variants may cluster in certain areas, particularly isolates from a single city collected over a short time.
Conclusions: The genetic variation among HIV-1 isolates is more extensive than previously appreciated. At least seven distinct HIV-1 genotypes can be identified. Diversification, migration and establishment of local, temporal 'blooms' of particular variants may all occur concomitantly.