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Salmonella might be the cause of the deaths of millions of Aztecs, new evidence suggests

Stefan Andrews

In one of the darkest episodes in history, the Aztecs suffered an unprecedented epidemic outbreak that claimed the lives of millions. It is largely accepted that it all began with the arrival of European explorers, who introduced new diseases to which the indigenous population had no immunity. Millions of people died in the first outbreak, an epidemic of smallpox that struck in 1519 and 1520.

Somewhere between 5 million and 15 million more lives were lost 25 years later, in another major disease outbreak. The locals started to refer to the malignant disease as “cocoliztli,” a word that otherwise means pestilence in Nahuatl, the native language of the Aztecs.

Aztec smallpox victims

Aztec smallpox victims

Roughly 80 percent of the Aztec population was lost in these epidemics and, for centuries afterward, questions lingered. What caused such a hazardous event that wiped out so many people? Numerous theories were brought to the table by experts and historians, but a conclusive explanation was not reached.

After five centuries, scientists finally seem to have some answers. The pathogen that caused high fevers, severe headaches, and bleeding from the nose, mouth, and even eyes may have been salmonella. In general, death followed within four days for the person who contracted this disease. Vast realms of Mexico were affected, with cases also reported in Guatemala and as far south as Peru.

Scientists have traced the presence of salmonella pathogen after conducting DNA analysis on skeleton remains of 29 bodies that were laid to rest in a massive graveyard known as Teposcolula-Yucundaa, a burial site associated with cocoliztli. They have identified the presence of the bacteria Salmonella enterica of the Paratyphi C variety on the teeth of the skeletons. The research findings were published in the journal Nature Ecology and Evolution in January 2018.

Åshild Vågene from the Department of Archaeogenetics at the Max Planck Institute in Germany, one of the study authors, commented that the pathogen would have caused enteric fever very similar to that of typhoid. Locals could have easily contracted the disease by simply consuming contaminated water or food.

The DNA analysis was carried out by making use of novel software that allows scientists to track down the presence of pathogens. Ten out of the 29 examined remains were linked to signs of the specific Salmonella pathogen.

The 1545-50 cocoliztli was one of many epidemics to affect Mexico after the arrival of Europeans, but was specifically the second of three epidemics that were most devastating and led to the largest number of human losses,” said Åshild Vågene.

Collapse of population in Mexico during the 16th century, attributed at least in part to repeated cocoliztli epidemics.

Collapse of population in Mexico during the 16th century, attributed at least in part to repeated cocoliztli epidemics.

Salmonella is a disease that you would normally catch through contaminated food or water sources,” she reports. “It would start in the gut, so finding it in the teeth suggests it had got into the bloodstream. The disease had spread everywhere in their body.” It means the individuals whose remains made up the subject of the recent study were indeed salmonella victims, not just carriers of the pathogen.

Vågene said it is only now that scientists have the technology and software needed to perform DNA analysis to yield answers to “a longstanding historical question.”

The recent study cannot alone confirm that the specific salmonella pathogen was the principal cause behind the historical epidemic. More rounds of DNA tests and research are needed to substantiate it.

Salmonella NIAID

Salmonella NIAID

The scientist suggests that perhaps there were other deadly microorganisms that played a role in the outbreak. Vågen and her team have analyzed a single group of skeletons retrieved from one graveyard only. It is uncertain if the pathogen was also present in other areas affected by the epidemics, she said.

Whether the arrival of Europeans on the continent was to blame for the salmonella fatalities is another question without a conclusive answer. However, historical records are clear that Europeans introduced several diseases to the indigenous people that they had previously not been exposed to, such as with smallpox.

Another recent study, one published in February 2017, said that the same variety of salmonella pathogen that was brought to the territory of Mexico in the 16th century was identified in DNA remains of a woman from Norway who passed away in 1200. This indicates that the particular deadly micro-organism was around on the European continent for at least three centuries before it traveled to Mexico.

Related story from us: The Aztec macuahuitl, a sword with obsidian blades, was sharp enough to decapitate a horse

Vågene has not excluded the possibility that salmonella was already present in Mexico before the arrival of Europeans. However, no evidence to back up such a claim has so far been found.

The 16th-century epidemics that killed millions of Aztecs remain among the deadliest that has taken place in human history. Two centuries before that, the “Black Death” bubonic plague wiped out 25 million Western Europeans, roughly half the population at the time.