Today I Discovered: The Mystery Epidemic That Wiped Out The Aztecs

In the 16th Century, over the course of five years, almost 80% of the Aztec population were wiped out due to an unknown disease that burnt through their villages, causing high fevers, bleeding from the mouth, nose and eyes and eventually lead to death. Without understanding the epidemic, the Aztecs named the phenomenon 'cocoliztli', their native word for 'pestilence'.

Scientists have pondered the potential cause of the cocoliztli epidemic for years, but only recently has new research uncovered what may have caused it.

Shortly after European settlers arrived in the New World, indigenous populations suffered severe population declines due to the introduction of infectious diseases that their bodies were not equipped to fight. Mexico's indigenous Aztec population is well-documented for being hit hard by a number of different infections over the years, including smallpox, measles and influenza, yet the diseases that wiped out much of the population shortly after Europeans arrived have been debated for more than a century.

A particularly devastating epidemic swept through the Aztecs in 1545, killing four out of five people, but the cause of this epidemic has been a point of contention.

Research detailed in Nature Ecology and Evolution and published online Monday suggests that a particularly nasty strain of bacteria may be to blame.

Salmonella Paratyphi C

Salmonella Paratyphi C is the cause of enteric fever, which results in muscle aches, fevers and a rash. It can also result in bleeding from the nose, ocular complications, vomiting and neurological problems. It still poses a major health threat today.

To come to this conclusion, the research team employed a new technology known as the MEGAN alignment tool (MALT), a piece of software that is designed to be used when DNA can be recovered from environmental samples.

Here, the research team used material gathered from individuals in a cemetery of the Teposcolula-Yucundaa region. Using tooth samples from 29 excavated skeletons, the team could recover ancient DNA and run them through MALT.

Think of MALT as a really powerful, all-seeing librarian. The research team wants to find a specific bacteria - a book - stored in a huge library of all possible bacteria that we know of. Instead of knowing the title of the book, the research team only have a single sentence to work with - DNA recovered from the tooth samples. It would take a long time to look at every book to find where that sentence fits, so they ask the librarian - MALT - which particular book most accurately matches the sentence.

After analysis, MALT found a wide number of books that the particular sentence fit in, but further analysis demonstrated that a subtype of Salmonella enterica, Salmonella Paratyphi C, was a strong candidate for causing the 1545 cocoliztli epidemic.

The team cautions that this is just a step toward understanding what may have caused the cocoliztli epidemic of 1545 and highlights the successful use of MALT in determining potential pathogenic agents involved in ancient diseases where the organisms that may be responsible are not already know.

[Nature Ecology & Evolution]


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