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Can microbiology tell us exactly what killed the Aztecs?

The arrival of the Spanish conquistadors to Mexico in the 1520s marked the beginning of the end for the indigenous people. With an estimated population of between 15 and 30 million at this point, this dropped dramatically to only two million by 1700: the result of battles, famine, drought, and perhaps most significantly, infectious diseases. The following Q&A investigates how microbiology contributed to the ruin of the once-flourishing Mesoamerican culture.

What is the ‘cocoliztli’ and how was it introduced to the Aztec population?

Previously, historians have established that the epidemics of 1545-1548 and 1576-1580 – also known as the ‘cocoliztli’, or ‘plague’ in the native Aztec language náhuatl – were imported by the Spaniards during their arrival. The indigenous population, who had no previous immunity against the newly introduced viruses, quickly succumbed to the diseases. Alongside these epidemics, the revolution of the social order, evangelization, destruction of ancient culture, and architectonic transformation all contributed to the start of the Colonial Era in Mexico.

When was the ‘cocoliztli’ first clinically documented?

In 1576, Spanish physician and naturalist Francisco Hernández and physician Alfonso Lopez de Hinojosos described the ‘cocoliztli’. In their account, they detailed a clinical condition that was highly contagious, although different from other diseases of the time such as smallpox, measles, and typhus. Symptoms of ‘cocoliztli’ included severe weakness, strong headaches, dry mouth, dizziness, and stomach pain and haemorrhages. They included that death could occur just four or five days after the appearance of the initial symptoms. Thus, this plague was referred to as haemorrhagic fever, or blood congestion.

Indigenous victims, Florentine Codex (compiled 1540–1585). As reproduced in: Fields, Sherry (2008). Public domain via Wikimedia Commons.

How has microbiology evolved to give us a better understanding of ancient epidemics?

In recent years, state-of-the-art technologies have allowed scientists to learn much more about today’s microbial world. By extension, these same technologies could allow insight into the causal agent of epidemics which struck centuries ago. Just one example of this is a 1998 study where teeth pulp was extracted from what were believed to be the remains of victims of the Bubonic Plague. As a highly vascularized tissue, it is conceivable that blood in the pulp – contaminated with bacteria, viruses, or both – could provide insight into the various pathogens that circulated in the bodies of long-ago diseased individuals. The detection of Yersinia pestis DNA sequences from the teeth pulp in this study was the first step in discovering the microbial history of the Black Death which decimated the European population in 1347-1351.

How do these developments help us pinpoint the causal agent of the ‘cocoliztli’?

Similar to the 1998 study, investigators extracted dental pulp from individuals buried in a cemetery associated with the ‘cocoliztli’, which led to the reconstruction of two causal agent genomes. These genomes were identified as the Paratyphi C strain of the pathogen Salmonella enterica, a causal agent of enteric fever, or typhoid fever, suggesting that this bacterium could have been involved in the Aztec plague. Known to be facilitated by the faecal-oral route, this species would have thrived in the poor sanitary conditions in Colonial New Spain, with the indigenous people immunologically defenceless against the infectious diseases of the Old Continent. Another study performed on ancestral DNA from skeletons found in Trondheim, Norway found the same bacterial genome in the dental remains of an individual buried in the 13th century. This suggests that Salmonella enterica was prevalent in Europe at least 300 years before the Spanish conquest of Mexico, reinforcing the hypothesis that it could have been transported there by asymptomatic carriers.

Is it possible that there were multiple causal agents of the Aztec epidemics?

It is quite possible that other diseases could have been involved in the ‘cocoliztli’. Findings from these previous studies are not conclusive evidence that Salmonella was the major causal agent of the decimation of the Aztec population. For example, standard symptoms of Salmonella Paratyphi C do not include gastrointestinal haemorrhage, leaving room for the distinct possibility that the ‘cocoliztli’ epidemics were a result of mixed infections.

How can researchers take a holistic approach to understanding infectious diseases of the past, present, and future?

As demonstrated across these studies, and throughout history, there is much to be learnt from the diseases which impacted our ancestors. The One Health concept allows for the visualisation of infectious diseases with a multi-discipline approach, combining cultural history with microbiology and systems biology, all alongside the relationships microorganisms have with their environment. The pathogenesis of disease and the ecology of pathogen transmission are vital not only for our understanding of the historical infections of the past, but also for us to learn how to better deal with the infections of the future.

Featured image credit: The Aztecs Pyramid at St. Cecilia Acatitlan, Mexico State by Maunus. Public domain via Wikimedia Commons

Recent Comments

  1. thom prentice phd

    It wasn’t “battles” that killed the Aztecs — it was GENOCIDE – flat-out murder; the white supremacist, white superiority bigotry of OU shows.

    Try telling the truth and stop looking for microbial reasons to excuse white Europeans and white North and South Americans from culpability in this ghastly war crime against humanity.

    It was the sword — and dogs tearing living human indigenous flesh from living indigenous bones — that caused the end of the Aztecs. The same typical excuses were offered for British behavior against the aborigines of Australia and the First Nations of Canada that continues to this minute – and for the US / Anglo / Nato devastation of North Korea, Vietnam, Iraq and Ukraine among others. So far.

    Except, of course, that the Aztecs weren’t killed off.

    Their descendants are alive all through central and northern Mexico — yet still oppressed, repressed and exploited by the mestizo rulers of Mexico — who seem to have more brutal white Spanish blood and sensibilities from Christianity-banned extramarital (and interracial) sex and rape and the occasional voluntary interracial marriage than — they have empathy for humanity let alone empathy for their own compadres among the large remaining Aztec population.

    True to form, white descendants of English conquistadors in North America further condemned the Aztecs to penury through “free trade agreements” — which allowed, among other things, the British bastard offspring United States to dump corn in Mexico, destroying indigenous sustainable family-farm-based agriculture and is driving indigenous populations to the large cities where they barely survive in unconscionable poverty.

    Oh. And go or try to go to the United States — except that now, after having destroyed indigenous Mexican / Aztec family lives and sustainable family farm agriculture the current emperor of the United States wants to build a “beautiful wall” to keep them out. And to keep out the Hondurans, Guatemalans and Salvadorans who, suffering from US-imposed brutal puppet regime dictatorships, seek to escape with their lives, no fortunes, but sacred honor intact.

    It is sort of like the US/UK/France/Nato invading and bombing every nation in the Middle East on behalf of lebensraum and empire for Israel and then denying entry to England for the refugees from the nations laid waste — from Libya to Iraq and from Afghanistan and Pakistan to Yemen and Somalia.

    So no. It wasn’t microbes. It was white supremacy (racism) and swords and guns and aerial bombing and drone bombing and the US and England arming the most wicked regimes on the planet.

    Why not tell the TRUTH?

    Cheerio! And have a pleasant day.

  2. Rudy Troike

    A serious historical misattribution regarding the pictures, comparable to labeling the Roman Coliseum as a Renaissance structure. Teotihuacan flourished so much earlier (c. 400 A.D.) that the Aztecs knew it only as a mythical site where the gods were born. (OUP of all people should be immune to such flubs!)

  3. Priscilla Yu

    Hi Rudy, many thanks for pointing out this mistake in the original featured image. We have replaced the photo and sincerely apologize for the misrepresentation.

  4. littlefoot

    @Thom Prentice, why use such abrasive language? Nobody doubts that the Spanish conquerors have heavily contributed to the steep Aztec population decline during the 16th century by treating them abysmally. And initially patogens from the old world also have taken a heavy toll. But that’s not exactly the subject of this article. This article is about what kind of patogens might’ve caused what the Aztecs called cocolitzli during later outbreaks. This is interesting insofar as 15 years ago there has been a widely publicised attempt to explain the plague with an outbreak of an indigenous sort of hantavirus. It was pointed out that a rodent population which harbored the dormant virus might’ve exploded after severe droughts and then floods. While it seems to be true that cocollitzli outbreaks coincided with periods of extreme weather conditions this theory fails to explain why the indigenous population was almost wiped out while the Spanish population was much less affected. This cannot be explained solely by their better living conditions. An indigenous virus should’ve affected the Spanish population much heavier than cocolitzli did.
    The new theory is interesting because for the first time a patogen has been isolated in actual bodies. If a vicious strain of salmonella really is a sufficient explanation for cocolitzli remains to be seen, though. IMO it’s more plausible than the hantavirus theory. The observation that the cocolitzli outbreaks coincided with extreme weather conditions (severe droughts followed by floods) might be valuable nevertheless. And poor living condidtions have of cause aggravated things for the indigenous population.

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