In the decades after Hernán Cortés invaded Mexico, one of the worst epidemics in human history swept through the new Spanish colony. A mysterious disease called “cocolitzli” appeared first in 1545 and then again in 1576, each time killing millions of the native population. “From morning to sunset,” wrote a Franciscan friar who witness the epidemic, “the priests did nothing else but carry the dead bodies and throw them into the ditches.”
In less than a century, the number of people living in Mexico fell from an estimated 20 million to 2 million. “It’s a massive population loss. Really, it’s impressive,” says Rodolfo Acuña-Soto, an epidemiologist at the National Autonomous University of Mexico. What can even kill so many people so quickly?
The Spanish, infamously, brought a litany of diseases unknown to the indigenous population—smallpox, measles, typhus—so some experts have suggested cocoliztli is simply one of those. Others, like Acuña-Soto, have argued it is an unknown viral hemorrhagic fever native to Mexico. The cause of cocoliztli has never been conclusively identified.
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