Phylodynamics of HIV-1 subtype B among the men-having-sex-with-men (MSM) population in Hong Kong

Abstract

The men-having-sex-with-men (MSM) population has become one of the major risk groups for HIV-1 infection in the Asia Pacific countries. Hong Kong is located in the centre of Asia and the transmission history of HIV-1 subtype B transmission among MSM remained unclear. The aim of this study was to investigate the transmission dynamics of HIV-1 subtype B virus in the Hong Kong MSM population. Samples of 125 HIV-1 subtype B infected MSM patients were recruited in this study. Through this study, the subtype B epidemic in the Hong Kong MSM population was identified spreading mainly among local Chinese who caught infection locally. On the other hand, HIV-1 subtype B infected Caucasian MSM caught infection mainly outside Hong Kong. The Bayesian phylogenetic analysis also indicated that 3 separate subtype B epidemics with divergence dates in the 1990s had occurred. The first and latest epidemics were comparatively small-scaled; spreading among the local Chinese MSM while sauna-visiting was found to be the major sex partner sourcing reservoir for the first subtype B epidemic. However, the second epidemic was spread in a large-scale among local Chinese MSM with a number of them having sourced their sex partners through the internet. The epidemic virus was estimated to have a divergence date in 1987 and the infected population in Hong Kong had a logistic growth throughout the past 20 years. Our study elucidated the evolutionary and demographic history of HIV-1 subtype B virus in Hong Kong MSM population. The understanding of transmission and growth model of the subtype B epidemic provides more information on the HIV-1 transmission among MSM population in other Asia Pacific high-income countries.

Figure 1. Bayesian phylogenetic tree of 125 subtype B pol sequences isolated from MSM in Hong Kong and 40 reference subtype B sequences.

Posterior probabilities >0.8 were shown at the nodes of the tree. Solid circle at the right indicate the branches were reference sequences isolated outside Hong Kong. Two HIV-1 subtype C sequences were used as outgroup in the tree. Bar, 0.05 nucleotide subsitution per site.

Figure 2. Bayesian Skyline Plot and dated phylogeny of the the Hong Kong MSM HIV-1 subtype B viruses.

Nonparametric reconstruction of the epidemic history with appropiate confidence limits and time-scaled phylogenies of the pol gene are shown. The demographic history of the subtype B virus among Hong Kong MSM represented in black, and the 95% confidence limits of the estimate are represented in grey. The tree represents the phylogenetic relationships of the sequences has the same time scale as the skyline plot.