Leprosy's Long History in Americas Unveiled

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."