XVIII International AIDS Conference


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Tracing the origin and evolutionary history of HIV-1 CRF28_BF and CRF29_BF in Brazil: implication to the continuous emergence of new recombinant forms

M.P.S. Chin1, N. Ristic1, J. Zukurov2, W. Alkmim3, R.S. Diaz2, M. Janini3

1Aaron Diamond AIDS Research Center, New York/NY, United States, 2Federal University of Sao Paulo, Department of Medicine, Sao Paulo, Brazil, 3Federal University of Sao Paulo, Department of Microbiology, Immunology, and Parasitology, Sao Paulo, Brazil

Background: CRF28_BF and CRF29_BF are genetically related HIV-1 intersubtype recombinants. They were first identified in 1999 and played a significant role in the AIDS epidemic in Brazil. It is not known about their origin and if either CRF or their related recombinants are still prevalent in the population. Here, we reconstructed the evolutionary history of CRF28 and CRF29 by coalescent inference to delineate the origin and epidemiology of these recombinants.
Methods: We used a Bayesian coalescent method to analyze the reverse transcriptase and envelope gene of Brazilian subtype B HIV-1 and BF recombinants. The rates of nucleotide substitution of the two HIV-1 genes were determined, and were used to date the phylogenies and reveal the evolutionary history of CRF28 and CRF29.
Results: The most recent common ancestor of Brazilian subtype B HIV-1 and variants of the CRF28/29 clade was dated back to about 1987.3 (95% HPD: 1979.1 - 1992.2). There is no significant difference between the phylogenies of CRF28 and CRF29 indicating that both strains have emerged at similar time possibility in related infection events. After the emergence of both CRFs, the effective number of infections by these recombinants grew exponentially between 1992 and 1997 but then decreased in infections toward the present following a logistic model of population growth. The decrease in infections by CRF28/29 appeared to have coincided with the emergence of CRF39_BF and CRF40_BF in Brazil.
Conclusion: CRF28 and CRF29 have coevolved since the late 1980's. The spreading of variants of the CRF28/29 lineage has diminished in recent years. However, intersubtype recombinants with diverse genotypes continue to emerge in the Brazilian population. This highlights the need for functional characterization on the replication capacity and antiviral susceptibility of these recombinants.

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