Multiple introductions and onward transmission of non-pandemic HIV-1 subtype B strains in North America and Europe.

Most HIV-1 subtype B infections in North America and Europe seem to have resulted from the expansion of a single pandemic lineage (B) disseminated from the United States (US). Some non-pandemic subtype B strains of Caribbean origin (B) may have also reached North America and Europe, but their epidemiological relevance in those regions remains largely unknown. Here we analyze a total of 20,045 HIV-1 subtype B pol sequences from the US, Canada, and Europe, to estimate the prevalence and to reconstruct the spatiotemporal dynamics of dissemination of HIV-1 B strains in those regions. We find that B strains were probably disseminated from the Caribbean into North America and Europe at multiple times since the early 1970s onwards. The B strains reached the US, Canada and at least 16 different European countries, where they account for a very low fraction (<5%) of subtype B infections, with exception of the Czech Republic (7.7%). We also find evidence of the onward transmission of B clades in the US, Canada, the Czech Republic, Germany, Italy, Spain and the UK, as well as short-distance spreading of B lineages between neighboring European countries from Central and Western Europe, and long-distance dissemination between the US and Europe.