HIV Diversity, Recombination and Disease Progression: How Does Fitness “Fitâ€? Into the Puzzle?

HIV appears to have diverged into several lineages upon multiple zoonotic introductions from thenonhuman primates. The HIV-2 and HIV-1 groups M, N, and O likely represent different cross-speciestransmission events. The radial evolution of group M in multiple clades or subtypes is likely due toadaptation and expansions in the human hosts. It is not well understood why HIV strains such asHIV-1 subtype C in particular or group M in general have spread disproportionately as compared toother subtypes, groups, or types, which often remained geographically constrained to local epidemics.Host genetic effects, transmission bottlenecks, social/behavioral and environmentallimitations, founder effect and other viral factors could have contributed to variable spread throughthe human population. Even after transmission, viruses evolve at different rates during diseaseprogression. Recent studies have explored phenotypic differences between HIV types, groups, andsubtypes in attempts to explain or understand this radial evolution and expansion. This reviewexplores some of the important aspects relating to fitness during disease progression, duringglobal distribution of different HIV subtypes, and related to circulation of recombinant forms in theepidemic.