Aztec apocalypse found to be Salmonella outbreak

By Dr. Ananya Mandal, MDJan 15 2018

There was an epidemic in the Mexican highlands in 1545 and then again in 1576 that killed between 7 and 17 million people. These people had fever and vomiting and developed red spots over their skin before they died.

These two epidemics essentially spelled doom for the Aztec Empire that died out soon after. There had been no evidence in the archeological findings to suggest the actual cause behind this mass wipe out.

Culture of Salmonella bacteria. 3D illustration. Image Credit: Tatiana Shepeleva / Shutterstock

A new study that appeared in the latest episode of the journal Nature Ecology and Evolution appeared yesterday (15th of January 2018) that reveals that scientists have found evidence that the culprit of the epidemic was Salmonella bacteria.

Kirsten Bos, a molecular paleopathologist at the Max Planck Institute in Germany, author of this new study says that plague and typhoid have both been suspected as the cause behind this wipe out. Other diseases were suspected as well she added. The epidemic is referred to as “cocoliztli” or “pestilence” because of the bleeding and vomiting. It killed people over Guatemala, Mexico and even Peru wiping out 80 percent of the population in the area. In this study the team of researchers thus analyzed the DNA obtained from the teeth of around 10 people who had died in the epidemic. They found evidence that a deadly strain of Salmonella could have been responsible. The 10 skeletons from which the DNA was obtained were found in a “cocoliztli” cemetery in Oaxaca, Mexico.

The team used a new technique that Bos called a “game changer”. This helped them to piece together the fragments of the centuries old salmonella DNA and identify it with accuracy. DNA has been extracted from archeological finds previously she explained. However this program helped them match it to the available databases of DNA to find out exactly what it was. The new program is called MALT or Metagenome analyzer (Alignment Tool). She added that this program helped them accurately identify several small DNA pieces to make a complete picture and identify the species to which those pieces of DNA belongs to.

The team used MALT and like reconstructing a jigsaw puzzle pieced together the DNA pieces that came from the teeth of the victims of the epidemic. Then it compared the sequences with the DNA databases of several pathogens until it found a match. PhD student and study author Ashild Vagene often had to manually compare sequences too at some points. The results of hours of work finally revealed that the DNA fragments belonged to a deadly Salmonella enterica Paratyphi C bacteria.

Now that the source is known, the researchers are looking for an origin of the bacteria. Whether the bacteria travelled to those regions via European invaders during the early 16th Century is being speculated. What is unclear is whether the Europeans got it from the local population or vice versa. It can be said that the indigenous population was susceptible to the infection. Bos said that the invaders changed the social landscape and there was an introduction of new livestock etc. All of the changes could have “increased their susceptibility to infectious disease,” she said. This may not be the only infection killing those millions Bos added. There could have been other deadly infections that were missed in this analysis she said.