A new study challenges the view that leprosy is a disease that was introduced into the Americas during European colonization. It reports that a strain of leprosy-causing mycobacterium, Mycobacterium lepromatosis, that was only discovered in recent years infected humans in the Americas longer ago – before European contact. The findings reshape current views of leprosy in the Americas and provide insights into the long-term interactions between humans and infectious diseases. There are two known mycobacteria that cause leprosy: Mycobacterium leprae and Mycobacterium lepromatosis. The former seems to have arrived in the Americas with European colonization and the latter was discovered in 2008 – and mostly reported in the Americas. To date, the only genomic data available from M. lepromatosis was obtained from three human samples from patients of Mexican origin and from seven red squirrels from Great Britain/Ireland, thereby limiting current understanding of the genetic diversity and history of the species. Here, Maria Lopopolo and colleagues sought to investigate the contemporary distribution and diversity of M. lepromatosis. They studied contemporary M. lepromatosis sequences, where data was available. To clarify the history and past prevalence of M. lepromatosis in the Americas, they also studied ancient DNA datasets from pre-European contact Ancestors from the Americas. Notably, the screening of pre-contact Ancestors uncovered three samples positive for M. lepromatosis in locations spanning the length of the Americas. “While our findings do not challenge the introduction of M. leprae leprosy into the Americas by European and African populations,” say the authors, “they reveal that M. lepromatosis was already circulating within human populations across the continent several centuries before the European arrival.”

In a Perspective, Mark Hanson and Peter Gluckman explore how maternal stress, caregiving quality, and early environmental conditions can shape the development of executive functions and emotional regulation in children, and how these factors contribute to the emergence of anxiety disorders in young people. Mounting evidence reveals a significant rise in anxiety disorders among adolescents ages 12 to 19, especially in developing countries like the United States, which cannot be fully explained by contemporary stressful events like the COVID-19 pandemic. This pattern suggests that broader longer-term societal or developmental factors are driving the growing prevalence of adolescent anxiety. Here, Hanson and Gluckman highlight how environmental conditions in the earliest stages of life – beginning even before birth – can significantly shape a child’s developing brain, particularly the systems responsible for emotional regulation and executive functioning. According to the authors, these early cues may "prepare" children for adversity, but if the anticipated threats never fully materialize as they grow, such heightened emotional responses may lead to anxiety disorders, especially in adolescence. This mismatch is further compounded by the rapid and dynamic social and technological changes young people now face. “Societies face an emerging burden of mental health issues, especially in young people. Although appropriate interventions are needed to help those already affected, preventative approaches are also critical,” write Hanson and Gluckman. “Solutions will need to adopt a lifecourse perspective, involving more cohesive thinking about parental and caregiver support and the early childhood years by policymakers across health, education, and social welfare."