In 1545, people in the Mexican highlands starting dying in enormous numbers. People infected with the disease bled and vomited before they died. Many had red spots on their skin.
It was one of the most devastating epidemics in human history. The 1545 outbreak, and a second wave in 1576, killed an estimated 7 million to 17 million people and contributed to the destruction of the Aztec Empire.
But identifying the pathogen responsible for the carnage has been difficult for scientists because infectious diseases leave behind very little archaeological evidence.