500-year-old teeth reveal an unimaginably deadly epidemic.

Popular Science checks the dental records to get to the cause of a mysterious sickness that killed up to 15 million people in only three years:

Red spots appeared on the skin, accompanied by wretched vomiting, bleeding from multiple orifices, and eventually, death.

It bore the name cocoliztli, meaning ‘pestilence,’ and it killed between five and 15 million people in just three years. As many plagues were at the time, it proved deadly and mysterious, burning through entire populations. Occurring centuries before John Snow’s work on cholera gave rise to epidemiology, data on the disease’s devastation was sparse. Over the years, researchers and historians attempted to pin the blame for the illness on measles, plague, viral hemorrhagic fevers like Ebola, and typhoid fever—a disease caused by a variation of the bacteria Salmonella enterica.

In a paper published this week in Nature Ecology & Evolution, researchers present evidence that the latter was the most likely candidate in this cast of microbial miscreants.

The researchers detected the genome of a different variety of Salmonella enterica (the specific variety is Paratyphi C) in teeth of individuals buried in a cemetery historically linked to the deadly outbreak.

Enteric fevers (mostly typhoid) continue to wreak havoc on the modern world. In 2000, they caused 200,000 deaths and 22 million illnesses globally. And just as we can be laid low thanks to a viral infection, so would our ancestors, though without the benefit of antibiotics and other modern treatments.