Alexandre Meneghini / AP
In 1545, the people of the highlands of Mexico began to die in enormous quantities. People infected with the disease bled and vomited before they died. Many had red spots on their skin.
It was one of the most devastating epidemics in the history of mankind. The outbreak of 1545 and a second wave in 1576 caused the death of between 7 and 17 million people and contributed to the destruction of the Aztec Empire.
But identifying the pathogen responsible for carnage has been difficult for scientists because infectious diseases disappear. behind very little archaeological evidence.
"There have been different schools of thought about what this disease was, could it have been a plague, could it have been typhoid, could it have been a litany of other diseases?" says Kirsten Bos, molecular paleopathologist at the Max Planck Institute in Germany, and author of a new study published Monday in Nature Ecology and Evolution .
The study analyzes the DNA of the teeth of 10 people who died during the epidemic and points to a possible culprit: a type of salmonella that causes a deadly fever.
A new algorithm allowed Bos and his team to identify fragments of ancient Salmonella DNA with extreme specificity.
"It was a technical analysis that was really the game change for us," explains Bos. While scientists were able to extract ancient DNA from bones and other tissues, until recently it was impossible to compare that extracted DNA with a wide variety of possible matches.
But a new computer program called MALT allowed them to do just that. "The biggest advance was this algorithm," says Bos. "It offers a method to analyze many, many, many small pieces of DNA that we get, and actually identifies, by species name, the bacteria that are represented."
Bos and his team used MALT to match the DNA fragments extracted from the teeth of the epidemic victims with a database of known pathogens. The program did not completely save them from the numbing work of the mind. At one point, the doctoral student and study author Ashild Vagene had to go through the results of the program at hand.
In the end, they found evidence of death Salmonella enterica Bacteria Paratyphi C.
The study does not identify the source of the bacterium, which is an area of great interest to biologists and archaeologists alike. The authors point out that it is believed that many epidemics of the period originated with European invaders that arrived in the region in the first part of the 16th century, but the new research does not present biological evidence for or against it.
A previous The study suggested that the pathogen responsible for the epidemic originated in Mexico and that the epidemic was aggravated by the drought. And, says Bos, "the Europeans who were observing the symptoms did not know what it was, and the Europeans also caught it," suggesting it was not an endemic disease in Europe.
But even if Europeans did not know how to introduce the pathogen, they may still be responsible for its profound lethality among indigenous peoples. "We know that Europeans changed the landscape a lot once they entered the new world," says Bos. "They introduced new cattle, [and] there were many social disturbances among the indigenous population that would have increased their susceptibility to infectious diseases."