Prevalence of unique HIV-1 recombinant forms (or intersubtype HIV-1 recombinants). The location of subtypes (e.g. A, C, G, etc), circulating recombinant forms (CRFs), and unique recombinant forms (URFs) are mapped in sub-Saharan Africa and specifically, Central Africain panel A. The number of humans infected with the dominant subtypes, CRFs, and URFs in the world or in Central Africa is graphed in panel B. The proportion of specific intersubtype recombinants (A/D, A/C, and others) responsible for URF infections in Central Africa has been reported (C) [20–23]. Panel D provides a neighbor-joining phylogenetic tree to describe the genetic relationship of the C1 to C4 env sequences of 115-A, 120-A, 89-D, 122-D, and 126-D to other reference HIV-1 sequences.