Scientists Are Just Now Figuring Out The Mysterious Disease That Nearly Wiped Out The Aztecs

For hundreds of years, history left us wondering what disease killed the Aztecs in the mid-1500s. Many assumed the Aztecs were one of many Central American groups to be wiped out by European diseases like smallpox. However, DNA testing has unearthed new evidence about what really killed 80% of the Aztecs. 

Scientists extracted DNA from Aztec teeth, and discovered the presence of a strand of Salmonella. Research on climate change in Mexico at the time indicates droughts could have precipitated the spread of disease. Some things remain unexplained, however; only continued research can explain how a massive epidemic ravaged the Aztecs and whether the invading Spanish introduced something fatal to the population. 


  • An Infectious Bacteria Was Responsible For Wiping Out Native Populations
    Photo: clundh / flickr / CC-BY-NC 2.0

    An Infectious Bacteria Was Responsible For Wiping Out Native Populations

    For many years, scientists theorized about what could have caused the virulent epidemic that . Some thought it was something like Ebola, while others assumed it was diseases brought by Spanish explorers.

    In January 2018, researchers discovered at least some of the Aztec population died from a strain of Salmonella called Paratyphi C, which presents itself as typhoid fever. Paratyphi C could have been spread via food or water.

    Others suspect this strain of Salmonella was spread via rodents. The Spanish forced the Aztecs into deplorable working conditions, putting them in a compromised physical state and in closer proximity to rodents. 

  • DNA From Teeth Helped Piece Together The Mystery

    By studying DNA from Aztec teeth, scientists discovered that Paratyphi C was responsible for the death of a portion of their population. German scientists examined the DNA taken from 29 skeletons in Mexico, and found the lethal bacteria.

    According to Åshild Vågene, one of the contributing researchers at the Max Planck Institute for the Science of Human History, skeletons typically do not show visible marks or traces of disease. In this case, they were able to use a new screening technique, the Megan Alignment Tool (MALT), to identify the Salmonella DNA sequences. 

  • There Is Still More DNA Testing That Needs To Be Done
    Photo: Kodez Ramirez / Wikimedia Commons / Public Domain

    There Is Still More DNA Testing That Needs To Be Done

    As groundbreaking as the DNA evidence of a bacterial infection may be, it's still only DNA from 29 deceased Aztecs out of the millions who died. Moreover, a Salmonella-like condition wouldn't cause bleeding from nearly every orifice. Some reports say the Salmonella bacteria was actually only found in 10 skeletons. There's also only one known burial site where anyone with the disease - known locally as cocoliztli - was buried. More burial sites need to be tested before anything can be said for certain. 

  • The Salmonella Still Does Not Explain The Bleeding Orifices
    Photo: Jean de Tovar / Wikimedia Commons / Public Domain

    The Salmonella Still Does Not Explain The Bleeding Orifices

    Some scientists believe the Aztecs perished due to a blood-borne illness. Though we now have at least a partial answer to the deaths of 80% of the population, the Salmonella infection doesn't explain the facial bleeding. 

    Francisco Hernandez, who was the physician of King Phillip II, provided a very descriptive written account of the condition affecting the Aztecs. Symptoms included fever, headaches, vertigo, dark urine, black tongue, large nodules on the neck and face, neurological problems, and, most notably, bleeding from the eyes, nose, and mouth.

    Researchers accept Hernandez's description, as he was arguably the most medically knowledgeable person of the time. These symptoms have yet to line up with one disease specifically. 

  • Roughly 15 Million People Died In Five Years
    Photo: The Field Museum Library / Wikimedia Commons / Public Domain

    Roughly 15 Million People Died In Five Years

    Starting in 1545, about 15 million people died over the course of five years. To put that number in perspective, 20 million people died from the bubonic plague in just a little under a decade. While these numbers and time spans are close, it is important to consider the 15 million who lost their lives to this disease were concentrated in Mexico, whereas the Black Death spanned all of Europe. 

    The Aztecs called this destructive disease cocoliztli, and it killed in a matter of days. Victims of this illness ran a high fever and then bled from the eyes, nose, and mouth.

  • Climate Conditions Didn't Help The Aztecs
    Photo: justin_vidamo / flickr / CC-BY 2.0

    Climate Conditions Didn't Help The Aztecs

    New evidence has shown cocoliztli was worsened by climate change. Between 1545 and 1576, there was a "megadrought" that spanned the entire continent. It was the worst drought in Mexico for over 600 years.

    Cocoliztli was notably absent from warmer, wetter areas like the Gulf of Mexico. Researchers were able to use tree ring evidence to figure out how much rain fell during those years, and they discovered a correlation between the drought and the massive deaths associated with cocolizti.