The dispersal of HIV-1 subtype B (HIV-1B) is a reflection of the movement of human populations in response to social, political, and geographical issues. The initial dissemination of HIV-1B outside Africa seems to have included the passive involvement of human populations from the Caribbean in spreading the virus to the United States. However, the exact pathways taken during the establishment of the pandemic in the Americas remain unclear. Here, we propose a geographical scenario for the dissemination of HIV-1B in the Americas, based on phylogenetic and genetic statistical analyses of 313 available sequences of the pol gene from 27 countries. Maximum likelihood and Bayesian inference methods were used to explore the phylogenetic relationships between HIV-1B sequences, and molecular variance estimates were analyzed to infer the genetic structure of the viral population. We found that the initial dissemination and subsequent spread of subtype B in the Americas occurred via a single introduction event in the Caribbean around 1964 (1950–1967). Phylogenetic trees present evidence of several primary outbreaks in countries in South America, directly seeded by the Caribbean epidemic. Cuba is an exception insofar as its epidemic seems to have been introduced from South America. One clade comprising isolates from different countries emerged in the most-derived branches, reflecting the intense circulation of the virus throughout the American continents. Statistical analysis supports the genetic compartmentalization of the virus among the Americas, with a close relationship between the South American and Caribbean epidemics. These findings reflect the complex establishment of the HIV-1B pandemic and contribute to our understanding between the migration process of human populations and virus diffusion.

Objective: To estimate the prevalence of the HIV-1 subtype B pandemic (B_PANDEMIC) and Caribbean (B_CAR) clades in Latin America and to reconstruct the spatiotemporal dynamics of dissemination of the B_CAR clades in the region. Design: A total of 7654 HIV-1 subtype B pol sequences collected from 18 different Latin American countries between 1989 and 2011 were analyzed together with subtype B reference sequences representative of the B_PANDEMIC (US/France = 300) and the B_CAR (Caribbean = 279, Panama = 37) clades. Methods: Phylogeographic and evolutionary parameters were estimated from sequence data using maximum likelihood and Bayesian coalescent-based methods. Results: Nonpandemic B_CAR strains were probably disseminated from the Caribbean islands of Hispaniola and Trinidad and Tobago into Latin America since the early 1970s. The B_CAR strains reached nearly all countries from Latin America here analyzed and in some of them were spread locally, although their overall prevalence in the region is low. The B_PANDEMIC clade comprises more than 90% of subtype B infections in most countries analyzed, with exception of Suriname, French Guyana and probably Guyana, where both B_PANDEMIC and B_CAR clades seem to circulate at a similar prevalence. Conclusion: This study demonstrates that nonpandemic subtype B lineages of Caribbean origin have been disseminated into Latin America shortly after the estimated introduction of subtype B in the continent. Despite their early dissemination, the B_CAR strains account for a minor fraction of current HIV-1 subtype B infections in the region that are mainly driven by spreading of the globally disseminated B_PANDEMIC clade.

In South America, the evolutionary history of influenza A virus (IAV) in swine has been obscured by historically low levels of surveillance, and this has hampered the assessment of the zoonotic risk of emerging viruses. The extensive genetic diversity of IAV in swine observed globally has been attributed mainly to bidirectional transmission between humans and pigs. We conducted surveillance in swine in Brazil during 2011–2020 and characterized 107 H1N1, H1N2, and H3N2 IAVs. Phylogenetic analysis based on HA and NA segments revealed that human seasonal IAVs were introduced at least eight times into swine in Brazil since the mid-late 1980s. Our analyses revealed three genetic clades of H1 within the 1B lineage originated from three distinct spillover events, and an H3 lineage that has diversified into three genetic clades. The N2 segment from human seasonal H1N2 and H3N2 viruses was introduced into swine six times and a single introduction of an N1 segment from the human H1N1 virus was identified. Additional analysis revealed further reassortment with H1N1pdm09 viruses. All these introductions resulted in IAVs that apparently circulate only in Brazilian herds. These results reinforce the significant contributions of human IAVs to the genetic diversity of IAV in swine and reiterate the importance of surveillance of IAV in pigs.