Scientists Discover What Killed the Aztecs After 500 Years

On Monday, scientists were able to set aside measles, mumps, smallpox and influenza as the likely suspects of killing the Aztecs. They have identified typhoid like ‘enteric fever’ for which they were able to find DNA evidence on the teeth of the long-dead victims of the disease.

Within five years, 15 million people which were about 80% of the population were wiped out in an epidemic named ‘cocoliztli’ that means pestilence. This disaster struck the Aztec nation of Mexico when people started coming down with headaches, high fevers along with bleeding from eyes, nose and mouth. They died in generally three to four days. The cause of the disease has been questioned for about five centuries.

Ashild Vagene of the University of Tuebingen in Germany said, “The 1545-50 cocoliztli was one of many epidemics to affect Mexico after the arrival of Europeans, but was specifically the second of three epidemics that were most devastating and led to the largest number of human losses,”

“The cause of this epidemic has been debated for over a century by historians and now we are able to provide direct evidence through the use of ancient DNA to contribute to a longstanding historical question.”

The outbreak was one of the deadliest epidemics in human history. The cocoliztli pestilence in 1545 in what is today Mexico and part of Guatemala after 20 years when smallpox killed about 5-8 million people in the wake of Spanish arrival. European colonizers spread diseases bringing such germs to local populations against which they had no immunity and had never faced before.

The second outbreak that lasted from 1576 to 1578 killed half of the remaining population.

“In the cities and large towns, big ditches were dug, and from morning to sunset the priests did nothing else but carry the dead bodies and throw them into the ditches,” is how Franciscan historian Fray Juan de Torquemada is cited as chronicling the period.

The scientists are now able to say that they might have caught the culprit. After analyzing the DNA extracted from 29 skeletons which were buried in the cocoliztli cemetery, traces of salmonella entrica bacterium were found of the Paratyphi C variety.

It is known to cause entric fever and one example of it is the typhoid fever. The Mexican subtype rarely causes human infection today. The research team said that many salmonella strains spread via infected food or water, and may have travelled to Mexico with domesticated animals brought by the Spanish.

“We tested for all bacterial pathogens and DNA viruses for which genomic data is available,” and salmonella enterica was the only germ detected, said co-author Alexander Herbig, also from Tuebingen University.


It is possible, however, that some pathogens were either undetectable or completely unknown. “We cannot say with certainty that S enterica was the cause of the cocoliztli epidemic,” said team member Kirsten Bos. “We do believe that it should be considered a strong candidate.”

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