Figure 7.

The current HIV-1 epidemic is a mixture of old and contemporary lineages. The dashed circle differentiates old and contemporary sequences. Inside the circle, the old sequences, such as the subtype E clade, may no longer exist in the current epidemic. We can only infer the ancient presence of subtype E based on CRF01_AE, a recombinant between subtype A and E. "X" represents a hypothetical extinct strain, "Y" represents a hypothetical old strain that is still circulating in the current epidemic, but hasn't been identified. CRF02 is an old recombinant derived from both old and contemporary subtype A and G. BF recombinants in South America and BC in China are new, as their parents are contemporary sequences. The black blobs (recombinants) and grey blobs ("pure" subtypes) are clades investigated in this paper, and white blobs are other HIV-1 clades.