Mysterious Cocoliztli Epidemics Killed Millions Across Mexico, but Historical Causes Remain Debated
Learn more about the Cocoliztli epidemics that swept through colonial Mexico, what may have caused them, and how they may have changed medicine.
In 1570, King Philip II dispatched his personal physician, Francisco Hernández, to Mexico — then known as "New Spain" — to investigate medicinal plants. During his expedition, Hernández witnessed the first Cocoliztli epidemic, which struck Mexico City with intense symptoms like black tongue, fever, swollen stomachs, and bleeding from various orifices.
The disease claimed hundreds of lives daily, potentially leading to millions of fatalities. Though less deadly than the Black Death, the first Cocoliztli is considered one of the worst demographic collapses in world history, comparable to the Black Death in its impact on humans.
Sandra Guevara Flores, a biological anthropologist at the Autonomous University of Barcelona, has studied the Cocoliztli epidemics for years. She posits that the first epidemic began in November 1544 and lasted until February 1546, with some estimates suggesting 5 million to 15 million deaths. The second Cocoliztli epidemic occurred from 1576 to 1578, killing an estimated 2 million to 2.5 million people.
Unlike smallpox, which had struck between 1519 and 1520, Cocoliztli lacked the distinctive hemorrhagic symptoms of that earlier pandemic. Nahuatl speakers named the disease "Cocoliztli," meaning "pest," a term often applied to subsequent pandemics over the following decades.
The origins of the Cocoliztli epidemics remain a subject of debate among scholars. In 2018, researchers from the Max Planck Institute discovered traces of Salmonella in a bloody shroud buried in Oaxaca, near the time of the first outbreak. Salmonella related to paratyphoid fever was considered a strong candidate for the first and deadliest outbreak of Cocoliztli.
However, the source of the epidemic in Mexico City, where the disease was most severe, remains unclear. While some researchers believe the second Cocoliztli epidemic might have been caused by a strain of hantavirus originating in Africa, further DNA evidence would be needed to confirm this hypothesis.
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