What evidence suggests that variola virus circulated before the 17th century?

Evidence that the variola virus circulated well before the 17th century is primarily derived from the recovery of viral DNA from human remains. Specifically, researchers have identified variola virus DNA in the teeth and bones of individuals who lived between 600 and 1050 CE, with remains uncovered in regions of modern-day Russia and Denmark.1

While some earlier historical theories suggested the disease may have emerged in Mesopotamia or the Nile River valley, those claims lacked concrete evidence. Additional historical context includes the introduction of the Latin term variola—meaning "pox" or "pustule"—by Bishop Marius of Avicentum around 570 CE, indicating the presence of an eruptive disease by that time.1