Preparation of a corpse, Florentine Codex Book 3

New Study Finds Salmonella Brought by Europeans Caused Epidemic that Wiped Out 80% of the Aztecs

For years, historians and scientists have said that much of the population of the New World died from infectious diseases brought by Europeans, for which the natives had little or no natural bodily defenses. Now a couple of new studies have found that it was Salmonella, along with war, that reduced Mexico’s population from an estimated 25 million to 1 million in the course of a century, effectively destroying the powerful Aztec civilization.

The first wave of the disease, in the 1540s, struck Mexico and killed as many as 80 percent of the nation’s inhabitants, says an article on about the new research, quoting a recent paper on bioRxiv. Scientists say they have discovered the stomach bacteria in remains of people buried in the 16 th century.

The Nature article, quoting a Danish DNA researcher who was not involved in the study, says this is the first genetic evidence of the disease that wiped out much of the native population after the Spanish colonized Mexico. The authors of the two articles are not responding to media inquires because they published their findings in peer-reviewed journals.

An Aztec Life-Death figure of the 900 to 1250 AD era

An Aztec Life-Death figure of the 900 to 1250 AD era ( Wikimedia Commons )

Major disease outbreaks were called cocoliztli ( pestilence) in the Aztec language Nahuatl . Two major outbreaks, one in 1545 and the other in 1576, are believed to have killed between 7 million to 18 million people in the Mexican highlands.

The Nature article quotes a Franciscan historian, who witnessed the cocoliztli of 1576 and wrote, “In the cities and large towns, big ditches were dug, and from morning to sunset the priests did nothing else but carry the dead bodies and throw them into the ditches.”

Other researchers have speculated variously that measles, smallpox or typhus were the germs behind the big disease events, but those have all been mooted, Nature says.

Aztec medicine

Aztec medicine (Florentine Codex, Book 11)

In the early 2000s, National Autonomous University of Mexico researchers said it may have been a viral hemorrhagic fever, in addition to a major drought, that caused the deaths. They said the epidemic’s magnitude was like that of the Black Death in Europe during the 1300s.

In one of these recent studies, evolutionary geneticist Johannes Krause and team at the Max Planck Institute for the Science of Human History, sequenced DNA from the teeth of 29 people buried in southern Mexico’s Oaxacan highlands. They determined several of the people were killed in the Salmonella pestilence that occurred from 1545 to 1550. DNA from their teeth matched Salmonella when compared to 2,700 modern bacteria genomes.

Arrival of Hernan Cortez by Diego Rivera in the Mexican Palacio Nacional, detail

Arrival of Hernan Cortez by Diego Rivera in the Mexican Palacio Nacional, detail ( Wikimedia Commons )

The Nature article states:

Further sequencing of short, damaged DNA fragments from the remains allowed the team to reconstruct two genomes of a Salmonella enterica strain known as Paratyphi C. Today, this bacterium causes enteric fever, a typhus-like illness, that occurs mostly in developing countries. If left untreated, it kills 10–15% of infected people…

Krause and his colleagues’ proposal is helped by another study posted on bioRxiv last week, which raises the possibility that Salmonella Paratyphi C arrived in Mexico from Europe.

The other team of researchers, headed by microbiologist Mark Achtman of the University of Warwick in Coventry, the United Kingdom, sequenced the genome of the Salmonella Paratyphi C from the remains of a woman who died around 1200 and whose remains were in a cemetery in Trondheim, Norway. This is the first evidence that the disease was afflicting people in Europe before they made contact with Mexican natives.

An evolutionary biologist who was not part of either study, Hannes Schroeder, said the presence of Salmonella Paratyphi C in Norway 300 years earlier than the so-called conquest of the New World isn’t proof that people from Europe communicated enteric fever in Mexico, but the theory is reasonable.  Also, he said, a small percentage of people can have the bacteria of Salmonella Paratyphi C without becoming sick. Mexicans would have lacked resistance to the disease.

The germ is transmitted in feces. In the chaos of famine and war, it’s possible the Spanish conquest caused bad sanitary conditions, which might have contributed to the spread of the disease.

Top image: Preparation of a corpse, Florentine Codex Book 3.

By Mark Miller


The theory sounds questionable as salmonella is not airborne. It's transferred thru contaminated foodstuffs and thru the contact with feces. The Aztecs, according to several historians were clean people, stout in stature but very muscular. Their habits of cleanliness were also noted, even to the point of washing the mouth after eating. A Salmonella 'epidemic' would imply filthy conditions and habits - not in keeping with the info noted by the first Europeans.  But again, this is just a theory. Airborne disease would stand a much better chance of decimating a population on this scale of this magnitude.  


Wasn't it true that human waste was used as fertilizer by the Aztecs? If so, this could have been a mechanism for transmission of the bacterium.

“If so”. But we don’t know, do we?. The salmonella bacterium is carried in many people guts, but doesn’t cause a problem. The NA’s didn’t have this bacterium. If the aztecs had been infected by the Euro’s, they likely would have become violently ill very quickly. Their civilization had survived centuries long before the Euro’s invaded. Using human waste would not have presented the problem if properly processed and applied, which, “if” they did use it, obviously didn’t cause this epidemic. But we still dont’ know they actually used human waste as fertilizer. I think it would be very unlikely they’de be using the ‘infected’ waste once the ‘epidemic’ had begun as it would be Diarrhea and it’s highly unlikely the Aztecs didn’t understand what that could mean. This whole theory presents a picture of these people wallowing around is human waste and squalor. Something we know was not a fact. I just feel this ‘theory’ is only that. The other problem of the ‘theory’ is the manner of transference. Again, Samonella is not airborne and is only transfered by contact with infected feces in some way. That’s an enormous number of people. The theory doesn’t seem to answer that question of how it spread. But we know the only way is can spread and it just doesn’t add up. 

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