A survey of HIV-1 strains circulating in the Tokyo-Kanagawa metropolitan area of Japan during 2004-2011 (n=477) identified six Japanese males (patients #1 through #6), who harbored viruses with genome segments derived from a distinct CRF01_AE variant uniquely found among MSM in China (designated CN.MSM.01-1). These six HIV infections were diagnosed in 2010-2011 among MSM (3 of 75) and men with unknown risk factors (3 of 63), and differed from the vast majority of HIV infections among MSM in Japan, which are overwhelmingly characterized by subtype B (239 of 246, 97.2%). Approximately one-third (91 of 239, 38.1%) of subtype B strains from MSM in Japan belong to a large monophyletic cluster (designated JP.MSM.B-1). In addition, we identified a smaller subtype B cluster (n=8) (designated JP.MSM.B-2) that also contains strains from two Chinese MSM living in Japan. Interestingly, patients #5 and #6 were found to be co-infected with CRF01_AE (CN.MSM.01-1) and subtype B (JP.MSM.B-2 or JP.MSM.B-1) variants that are unique to the HIV-1 epidemics among MSM in China and Japan, respectively. Our study demonstrates for the first time the effect of the expanding HIV epidemic among MSM in China on transmission in neighbouring countries, and shows the ongoing mixing of CRF01_AE and subtype B lineages unique to HIV-1 that co-circulate in MSM populations in East Asia. This finding highlights the importance of strengthening epidemiological surveillance in the region and the need for effective measures to limit transmission among MSM in East Asia.
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