[HIV-1 diversity: a tool for studying the pandemic].

HIV-1 is remarkable for the diversity of strains comprising the HIV/AIDS pandemic. In the last decade, classification of viral variants as groups, subtypes, and circulating recombinant forms (CRF) and the observation of specific mutational patterns have become powerful tools for studying viral molecular dynamics. Monitoring the worldwide distribution of HIV-1 diversity has been used in both epidemiological surveillance programs and in reconstructing the history of regional epidemics. Specific patterns of virus spatial distribution also suggest differences in pathogenicity and transmissibility among the various subtypes. Molecular analyses of viral sequences allow estimating the rate of divergence among variants and the dynamic forces shaping the phylogenetic trees.