School of Human Evolution and Social Change, Arizona State University
Thursday 10:30-10:45, Ballroom A
The origin and ecology of leprosy, an ancient human scourge, remain poorly understood. Mycobacterium leprae, the causative agent of leprosy, exhibits a parasitic lifestyle based on extensive genome decay that happened millions of years ago, suggesting M. leprae may have been present in primates long before modern humans. In contrast, very limited genetic variation among strains of distant geographic locations suggests a recent jump to humans. To explore the evolutionary history of leprosy, we sequenced the genome of an M. leprae isolated from a West African mangabey. Further, to assess whether other non-human primates are also affected by leprosy, we surveyed wild chimpanzees and ringtail lemurs using qPCR of DNA extracted from cheek swabs or wadges.
Our analyses show that the mangabey strain is closely related to human strains. Human West African and the mangabey strains are ancestral to Eurasian strains, supporting an Africa origin of leprosy. To determine the timeframe of disease spread, we calculated M. leprae’s substitution rate from the estimated divergence time between M. leprae and M. tuberculosis. The latter was obtained using 101 homologous proteins across 27 bacterial taxa and a Byesian relaxed-clock framework calibrated with biogeochemical events. Our findings support the spread of leprosy from Africa to Europe and Asia around 10,000 years ago. The role primates play in the ecology of human leprosy remains unknown. New World nine banded armadillos that are infected with leprosy in their entire range, however, have been implicated as possible zoonotic source for human leprosy more recently.