Figure 4. Relationship between the increasing prevalence of HIV-1 subtype C and its low pathogenic fitness.

The prevalence of HIV-1 subtype C or subtype C-containing recombinant forms has increased in proportion to other HIV-1 subtypes in Rio do Sul, Brazil (from 35% in 1996 to 52% 2002)¹³³, in Kinshasa and Mbuji-Mayi, Democratic Republic of Congo (DRC) (from 2.1% and 16.3% in 1997 to 9.7% and 25% in 2002, respectively)¹³⁴ and in Yunnan, China (from 5.1% in 1992 to 90% in 2002)^162,163. By contrast, subtype C is dominant in South Africa¹⁶⁴ and did not increase in proportion to subtypes A and D or recombinant forms in Kenya¹⁶⁵. The number of HIV-1 cases increased in all of these regional epidemics (except in Kinshasa)⁶. a | The number of HIV-1 infections in specific years is subdivided into subtype C (yellow) and non-subtype-C (maroon) HIV-1 infections. b | A schematic representation of the pathogenic fitness of human lentiviruses, derived from >3,000 pair-wise dual HIV-1 competition experiments^{26,27,49,50,108,120,123,125,165}. The coloured ovals plot the fitness of primary HIV-1 isolates competed against isolates of the same type, group or subtype (y axis; mean fitness of 1 or equal fitness) compared with the fitness of primary HIV-1 isolates competed against isolates of different types, groups or subtypes. Each oval encompasses the fitness (x and y fitness values) of at least 10 to 20 primary HIV-1 isolates. M, main; O, other.