In 1570, King Philip II sent his personal physician to Mexico — then colonized as “New Spain" — on an expedition to learn more about medicinal plants in the region. On his trip, Francisco Hernández spent the first few years getting introduced to Indigenous foods such as cacao, corn, pineapple, and other fruits that would find great success in Europe. He even described hallucinogenic drugs like peyote. But nothing would have prepared him for the hands-on medical work that occurred when the second Cocoliztli epidemic tore through the population of Mexico City.
Patients suffered from intense symptoms like black tongue, fever, swollen stomachs, and bleeding from the nose, eyes, and mouth. Victims usually died within three or four days.
His description of the second Cocoliztli epidemic was remarkably detailed for the time. The disease was killing hundreds of people per day, at least, in just one area near Mexico City, and perhaps went on to kill millions by some estimates. If the latter is true, this epidemic, and the first Cocoliztli epidemic — that preceded it by about three decades — could be among the worst diseases to ever affect humans on our planet.
But compared to other deadly epidemics like the Black Death of Europe’s mid-14th century, we know very little about Cocoliztli. Academics don’t even agree on the little that we do know, other than the fact that these waves of deaths had a massive impact on the future of relationships between Indigenous Mexicans and European colonizers.
Explore All Options“This was one of the great demographic collapses in world history,” David Stahle, a professor emeritus in geosciences at the University of Arkansas in Fayetteville, told Discover. “This is up there with the Black Death in terms of the impact on humans.”
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The Cocoliztli Epidemics Killed Millions
Sandra Guevara Flores, a biological anthropologist at the Autonomous University of Barcelona, has studied the Cocoliztli epidemics for years. She says the first epidemic began around November 1544, carrying on through February 1546.
While Stahle and his colleague Rodolfo Acuna-Soto believe it was the deadliest, possibly killing 5 million to 15 million, the first Cocoliztli has comparably little description compared to the second, according to a study in Emerging Infectious Diseases. Guevara Flores explained that historical sources mostly describe nosebleeds, high fever, and death after three days. These hemorrhagic symptoms differ from smallpox, which had killed millions between 1519 and 1520. It also didn’t appear similar to other major European diseases known to have killed a lot of Indigenous Americans, such as measles, typhus, or mumps.
Nahuatl speakers called it Cocoliztli, which translates to “pest,” and the name is often applied to subsequent pandemics that occurred over the ensuing decades. But many of these may not have been the same thing.
The second big epidemic occurred from 1576 to 1578, Guevara Flores said. While less deadly than the first, it was still devastating, killing 2 million to 2.5 million people, Acuna-Soto estimates.
Potential Causes of the Cocoliztli Epidemics
Compared to pandemics such as the Black Death, anthropologists have found very little evidence of Cocoliztli outbreaks. One exception is a 2018 study published in Nature Ecology and Evolution. Researchers from the Max Planck Institute analyzed the DNA in a bloody shroud buried with human remains in Oaxaca dating to around the time of the first outbreak and found traces of Salmonella. The team stated that a kind of Salmonella related to paratyphoid fever was “a strong candidate” for the first and deadliest outbreak of Cocoliztli.
The latter statement is controversial among scholars, though. “This [Salmonella] strain could have been very deadly compared to what we see today,” Miriam Bravo-Lopez, who studies ancient pathogens at Arizona State University, told Discover.
Bravo-Lopez worked on a preprint study with Guevara Flores that finds that Europeans likely introduced the Salmonella enterica Paratyphi C found in the Oaxaca shroud and in other remains.
But neither of them, nor Stahle, believes that this strain of Salmonella was solely responsible for the initial Cocoliztli epidemic.
Guevara Flores told Discover that the DNA tests were conducted in Oaxaca, not Mexico City, and it’s unclear from historical records whether the first Cocoliztli experience in the capital was the same as Oaxaca. Records in Oaxaca describe symptoms like vomiting, diarrhea, skin pustules, and other problems that were more like Salmonella than the nosebleeds, quick death, and high fever experienced in Mexico City at the time.
If Salmonella was involved in the Mexico City deaths, it likely wasn’t the only thing. Whatever else was infecting them may have put victims in a weakened state where Salmonella could more easily take hold.
“Probably their immune system was very poor, and they found Salmonella because this pathogen may have been just taking advantage of their immune system,” Bravo-Lopez said.
“There may well have been overlapping epidemics,” Caitlin Pepperell, a microbiologist and physician at the University of Washington who studies pathogen evolution, told Discover.
As for the second Cocoliztli epidemic in the mid-1570s, Guevara Flores speculates it was caused by hantavirus, based on similarities in symptoms. She believes it was a strain from Africa based on hemorrhagic symptoms. But researchers have yet to find solid traces of this disease — excavations at known disease burial sites would be needed to search for more DNA that could provide clues.
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Why Was Cocoliztli So Deadly?
Not everyone agrees with the numbers of deaths projected by Acuna-Soto and Stahle. Guevara Flores said it’s very difficult to tell how many were killed, partly because census data recorded by the Spaniards is often inaccurate, particularly in the 16th century. But she believes their estimate of millions dead may be way too high — the smallpox epidemic earlier in the 16th century was likely far more deadly, she added.
Whatever it was, and whatever the numbers, these outbreaks didn’t happen in healthy conditions.
Stahle’s expertise lies in tree-ring dating, from which he determined that most of these epidemics can be related to times of drought. They either occur in the midst of a drought or in the year following one. He notes that one of the biggest prolonged droughts in Mexico occurred from the 1540s to about 1580.
This dry spell would have caused profound stresses on food availability and health. Indigenous Mexicans were already reeling from the impacts of the Spanish encomienda system, a brutally repressive legal framework the Europeans used to extract goods and labor. After the Aztec conquest in central Mexico in 1521, many Indigenous people were forcibly displaced and likely enslaved. All this, combined with malnutrition, contributed to a vulnerable state of health.
“That will make a disease that is normally grumbling along appear incredibly dramatic,” Pepperell said.
Furthermore, the Mexican climate was affected by the Little Ice Age, a weather pattern that affected much of the world from roughly the 16th to the 19th centuries. Indeed, deaths in the Cocoliztli epidemics seem to have been worse in the winter, which was abnormally cold for the region, Guevara Flores said.
The Impact of the Cocoliztli Epidemics
Scholars may not agree on the number of deaths the Cocoliztli epidemics caused. But they all agree the epidemics had long-lasting impacts. The first Cocoliztli had such an impact on Indigenous people that the Spanish crown paused taxation on them until 1560, while the European settlers were still on the hook.
Another major impact was on medicine itself. European and Indigenous medicine didn’t have a lot of intersections before, but Cocoliztli seems to have affected settlers and locals alike.
As a result, Guevara Flores explained that these traditions ended up coming together in some ways to create a “contact medicine,” incorporating theories from Indigenous people and Europeans.
“The whole society was really affected by them,” Guevara Flores, who comes from Mexico originally, told Discover.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in Emerging Infectious Diseases: Megadrought and Megadeath in 16th Century Mexico
- This article references information from a study published in Nature Ecology: Salmonella enterica genomes from victims of a major sixteenth-century epidemic in Mexico
