Have Researchers Discovered What Caused the 16th Century Mexican Epidemic That Killed Over 80% of the Population?
A pair of recently published studies point the finger at a deadly form of salmonella as the cause of millions of deaths in a 16th century Mexican epidemic outbreak. This cocoliztli (pestilence in Nahuatl) occurred from 1545-1576 and took the lives of between 7 and 18 million people – leading some researchers to draw parallels with the Black Death that struck Eurasia in the 14th century.
The journal Nature reports that the native population of Mexico was around 25 million when Hernando Cortés arrived in 1519, but just a century later there were only 1 million people remaining. The primary cause for this dramatic decrease in population was apparently two major outbreaks of cocoliztli, one in 1545 and the other in 1576. As Dr. Acuna-Soto, a professor of epidemiology on the Faculty of Medicine at the National Autonomous University (UNAM) of Mexico wrote “In absolute and relative terms the 1545 epidemic was one of the worst demographic catastrophes in human history, approaching even the Black Death of bubonic plague.”
The 16th-century population collapse in Mexico, based on estimates of Cook and Simpson. (1948) ( Public Domain )
There has been a great deal of debate over what cocoliztli was, though small pox, measles, a viral hemorrhagic fever , and typhus have all been suggested to have been behind the epidemics.
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In Acuna-Soto’s article, published in The American Society of Tropical Medicine and Hygiene in 2000, he wrote that his team’s research showed that the illness:
“was characterized by an acute onset of fever, vertigo, and severe headache, followed by bleeding from the nose, ears and mouth; it was accompanied by jaundice and severe abdominal and thoracic pain as well as acute neurological manifestations. The disease lasted three to four days, was highly lethal, and attacked mainly the native population, leaving the Spanish population almost untouched.”
Indigenous victims of disease from the Florentine Codex (compiled 1540–1585). ( Public Domain )
But now, a team led by Johannes Krause at the Max Planck Institute for the Science of Human History in Jena, Germany have discovered a strain of Salmonella enterica known as Paratyphi C in the DNA from the teeth of 29 people buried in an early contact era epidemic cemetery at Teposcolula-Yucundaa, Oaxaca in southern Mexico. Ewen Calloway’s article in Nature describes the main symptom and possible effects of this bacterium, it “causes enteric fever, a typhus-like illness […] If left untreated, it kills 10–15% of infected people.”
The study, published in bioRxiv , suggests that the Salmonella Paratyphi C may have arrived in Mexico from Europe along with the “variety of plants, animals, cultures, technologies […that] accompanied the movement of people from the Old World to the New World immediately following initial contact, in a process commonly known as the “Columbian exchange.””
A) The location of the Teposcolula-Yucundaa site in the Mixteca Alta region of Oaxaca, Mexico; B) central administrative area of Teposcolula-Yucundaa showing the relative positioning of the Grand Plaza and churchyard cemetery sites. C) drawing of individual 35 from which the Tepos_35 S. Paratyphi C genome was isolated. ( Teposcolula-Yucundaa archaeological project archives - INAH )
Coincidentally, a team led by Mark Achtman, a microbiologist at the University of Warwick in Coventry, UK, have also recently presented their results on a study of a woman from Norway who died from enteric fever caused by Salmonella enterica Paratyphi C about 300 years before the epidemic hit Mexico.
An odd coincidence? Or is there a chance that the same bacterium spread throughout Europe to reach Spain and then got carried over to the ‘New World’ when the Spanish arrived in Mexico in the 1500s?
It may be possible. As Calloway points out “A small percentage of people infected with Salmonella Paratyphi C carry the bacterium without falling ill, so apparently healthy Spaniards could have infected Mexicans who lacked natural resistance.”
An illustration from Historia de las Indias de Nueva España e islas de la tierra firme (1579) by Diego Durán showing Aztecs and Spanish conquistadors fighting. ( CC BY SA 4.0 )
The chaos that surrounded their arrival would have altered the hygienic conditions in the area as well, with forced relocation, new farming practices, etc. increasing the likeliness of food or water contamination. Drought conditions would have worsened the situation.
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However, the ties between the studies are a little too thin for some researchers. María Ávila-Arcos, an evolutionary geneticist at UNAM, for example, isn't convinced; saying that it is more likely a virus caused the cocoliztli – something that the researchers’ methods wouldn’t have picked up in the current study.
Nonetheless, it would be interesting to compare the ancient genomes of the Salmonella strains from Mexico and Norway, as well as others collected from across the Americas and Europe, to test this hypothesis and see if the bacterium was brought in from Europe.
In fact, Krause’s team plans to continue their search for ancient pathogens in Caribbean burial sites, to see if other evidence will support their Salmonella hypothesis.
Top Image: Preparation of a corpse. Florentine Codex Book 3. Source: Mexicolore
There seems to be strong evidence that the "black death" plague of Europe was caused by some form of airborne ebola virus, not the flea-bite transfer of bacteria that we were taught.
The presence of salmonella in the corpses of Aztec plague victims argues that they weren't properly prepared and that you shouldn't eat them (scavengers and cannibals be warned), but not necessarily that they died from salmonella. You can be confident that the chicken that is left out on your counter, though it might be teaming with salmonella, actually died from getting its head lopped off at the processing plant, not from a bacterial infection.
Rotting bodies team with all kinds of dangerous bacteria that aren't necessarily the cause of death, and in a plague these bacteria can be transferred from body to body by the people handling the corpses. That's why we warn kids not to touch dead things in the woods.