Leprosy has been present in the Americas for more than 1,000 years, long before the arrival of European settlers, according to a groundbreaking new international study co-led by scientists at Colorado State University and the Institut Pasteur in France, in collaboration with Indigenous communities and more than 40 scientists from institutions across the Americas and Europe. The study reframes the history of leprosy in the Americas and has implications for better understanding how infectious diseases spread, persist and evolve in human and animal populations over time.

A large-scale genomic analysis reveals Brazil as one of the most genetically diverse countries on Earth – shaped by centuries of colonization, forced migration, and Indigenous heritage, researchers report. The study, which leveraged newly generated whole-genome sequences of over 2,700 individuals, uncovered more than 8.7 million previously undocumented genetic variants, including those potentially affecting population health. The colonization of Brazil by Europeans from the 15th to 20th centuries resulted in one of the most profound population displacements in history; around five million European settlers and at least five million enslaved Africans were forcibly brought to a region that was home to more than 10 million Indigenous people. As a result, Brazil today is home to exceptional genetic and cultural diversity – it is the most admixed nation globally, hosting over 200 million people descended from these diverse populations.

However, despite this rich and complex genetic heritage, fine-scale studies of Brazil's genetic population structure – which hold implications for health – remain limited. Whole-genome analyses focused on the Brazilian population are largely undone. To fill these critical gaps, Kelly Nunes and colleagues generated whole-genome sequence data from 2,723 individuals across Brazil, capturing a wide range of ethnic, geographic, and cultural backgrounds. Analysis of this data revealed that Brazilian genomes are among the most genetically diverse globally, containing novel haplotypes rooted in Indigenous American, African, and European ancestries. Notably, Nunes et al. uncovered over 8.7 million previously undocumented genetic variants – more than 11% of all variants in the dataset – many of which were absent from major global databases. Some of these variants lie in regulatory and protein-coding regions that may influence traits like fertility, metabolism, and immunity. The authors also identified 36,637 rare and potentially harmful variants that were more common in individuals with African or Indigenous American ancestry.