Molecular dating of HIV-1 subtype C from Bangladesh.

Bangladesh has an overall low HIV prevalence of <0.1% in the general population and <1% among key affected populations, but it is one of few Asian countries that has yet to reverse the epidemic. In order to do this, it is important to understand the transmission dynamics in this country. The aim of this study was to investigate the phylogenetic relationships of HIV-1 subtype C strains from Bangladesh and related strains from other countries, and thereby clarify when and from where subtype C was introduced in the country and how it subsequently spread within Bangladesh. The phylogenetic analysis included 118 Bangladeshi gag sequences and 128 sequences from other countries and was performed using the BEAST package. Our analysis revealed that the vast majority of Bangladeshi sequences (97/118, 82%) fall into a large regional cluster of samples from Bangladesh, India, China and Myanmar, which dates back to the early 1960's. Following its establishment in the region, this strain has entered Bangladesh multiple times from around 1975 and onwards, but extensive in-country transmission could only be detected among drug users and not through sexual transmission. In addition, there have been multiple (at least ten) introductions of subtype C to Bangladesh from outside this region, but no extensive spread could be detected for any of these. Since many HIV-infections remain undetected while asymptomatic, the true extent of the transmission of each strain remains unknown, especially among hard to reach groups such as clients of sex workers and returning migrants with families.