RESUMEN
HIV-1 strains have diversified extensively through mutation and recombination since their initial transmission to human beings many decades ago in central Africa. The high error rate of HIV reverse transcriptase combined with the estimated in vivo HIV-1 replication rate of ten billion new virions each day leads to extraordinary genetic diversity of HIV. Twenty seven circulating genetic forms of the HIV-1 group M are presently recognized, including 11 subtypes and sub-subtypes, and 16 circulating recombinant forms (CRF). Genotypic analyses have provided a better understanding of the molecular diversity of HIV-1, enabling the detection of emerging HIV-1 variants and improving the tracking of the epidemic worldwide. The rapid evolution of HIV within infected hosts contributes significantly to the elusiveness of this pathogen from host antiviral responses. The complex nature of HIV envelope glycoprotein that is inherently resistant to neutralization, the selective infection, progressive destruction and impaired regeneration of CD4+ T helper cells, generation of cytotoxic T lymphocyte (CTL) escape mutants, together with high genetic diversity with continually evolving HIV variants worldwide, makes design of an effective vaccine a formidable task. Given the rapidity and unpredictability with which HIV-1 genetic forms may propagate in future, a vaccine protective against all major HIV-1 circulating genetic forms is desirable, which could require multivalent formulations. Understanding the kinetics and directions of this continuing adaptation and its impact on viral fitness, immunogenicity and pathogenicity are crucial to the successful design of effective HIV vaccines. In this review, we focus on extensive diversity of HIV-1, emergence of recombinant forms and their impact on diagnosis, antiretroviral therapy, disease progression, transmission, and vaccine development.