High prevalence of diverse forms of HIV-1 intersubtype recombinants in Central Myanmar: geographical hot spot of extensive recombination.

OBJECTIVES: To investigate the molecular epidemiology and genetic structure of HIV-1s causing the epidemic in Central Myanmar and to explore the genesis of HIV epidemic in this area.
DESIGN: A molecular epidemiological investigation was conducted in 1999-2000 in the city of Mandalay among high-risk populations and the structural features of circulating HIV-1s were analyzed.
METHODS: HIV-1 genotypes of 59 specimens were screened based on gag (p17) and env (C2/V3) regions. Near full-length nucleotide sequences of HIV-1 isolates with subtype discordance were determined and their recombinant structures were characterized.
RESULTS: Three lineages of HIV-1 strains, including CRF01_AE (27, 45.8%), subtype B' (Thailand variant of subtype B) (15, 25.4%) and subtype C (8, 13.6%), were distributed in Mandalay, while substantial portions (9, 15.3%) of specimens showed various patterns of subtype discordance in different regions of HIV-1 genomes. The study on six HIV-1 isolates with subtype discordance revealed that they were highly diverse types of unique recombinant forms (URFs) comprised of various combinations of three circulating subtypes. One URF was a particularly complex mosaic that contained 13 recombination breakpoints between three HIV-1 subtypes. Approximately half of recombinants showed 'pseudotype' virion structures, in which the external portions of envelope glycoproteins were exchanged with different lineages of HIV-1 strains, suggesting the potential selective advantage of 'pseudotype' viruses over parental strains.
CONCLUSION: The study revealed the unique geographical hot spot in Central Myanmar where extensive recombination events appeared to be taking place continually. This reflects the presence of highly exposed individuals and social networks of HIV-1 transmission.