Molecular epidemiology of HIV-1 in MSM
Recent reports from molecular epidemiology, phylodynamic studies, and HIV virology are providing insights into transmission and acquisition risks for MSM, transmission dynamics in MSM networks, and challenges to HIV prevention for these men. In a 2008 report on HIV transmission dynamics across the city of London,
episodic bursts of transmission in large linked clusters were identifi ed as characteristics of transmission within MSM populations.
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About 25% of all HIV infections in MSM were linked to one of several clusters. Later work noted that only 5% of infections in UK heterosexuals were similarly linked, and that infections were spreading much more slowly within heterosexual networks than homo sexual ones.
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Investigators who used single-genome amplifi cation and a model of viral evolution in a cohort of acutely infected US MSM
noted that MSM were more than twice as likely as heterosexually exposed people to be infected with multiple HIV viruses (p=0ท042). They also reported on the other available studies (n=5), which showed that this substantially higher rate of multiple-variant transmission held for MSM compared with heterosexual samples (p=0ท008), and that 38% of acutely infected MSM had multiple variants. The investigators attributed this higher rate to the epidemiological risks these men reported: receptive anal intercourse with many partners and the diff ering anatomical and immuno histological characteristics of the male and female genital tracks