Scientists believe they may have discovered the cause of an epidemic that struck Mexico’s Aztec empire in 1545, killing up to 15 million people.
In a paper published in Nature Ecology & Evolution, they describe how DNA extracted from the teeth of 29 skeletons buried in a cemetery in southern Mexico was revealed previously unidentified traces of the salmonella enterica bacterium.
The bacterium is known to cause enteric fever, of which typhoid is an example. The symptoms tally with those mentioned in records from the time, which describe victims developing red spots on the skin, vomiting, and bleeding from various body orifices.
The epidemic was one of several to hit the indigenous Aztec population soon after the arrival of Europeans in the early 16th century.
Its cause has been debated for more than a century. Measles, pneumonic plague and influenza have all been suggested as possibilities.
The Aztecs themselves gave the 1545-1550 outbreak the name “cocoliztli”, a generic term meaning “pestilence” in the Aztec Nahuatl language.
Although estimates vary, the epidemic likely wiped out between five and 15 million people – up to 80 per cent of the population.
It came just two decades after a smallpox epidemic that killed up to eight million people just after the Spanish arrival and is considered one of the most devastating epidemics in human history.
It affected large areas of central Mexico and Guatamala, perhaps extending as far south as Peru.
While many of the epidemics that swept through the Americas between the 16th and 19th centuries were undoubtedly a result of infectious diseases introduced by European colonisers, the scientists involved in this study cannot be certain that it was Europeans who introduced salmonella to the Aztecs.
Several factors point towards this conclusion, however. Comparing the DNA of Aztec people who died before and after the conquest, they discovered no trace of the bacterium in the former and often significant traces in the latter.
There is also evidence that salmonella enterica existed in Europe well before the Spanish began their conquest of the region.
Elizabeth Graham, professor of archaeology at University College London, offered a different interpretation of the findings.
“Salmonella wasn’t necessarily the root cause of the epidemic,” she told The Independent.
People may have been getting sick because of a different disease, which meant that they were less able to look after themselves and each other, increasing the risk of salmonella.
“The diseases themselves weren’t the only problem,” Professor Graham explained. “Everyone was hit at once. No one was able to care for anyone else. Salmonella may be a sign of people not being able to care for one another.”
But she welcomed the research and the development of enhanced DNA analysis tools that enabled it.
“Even today, diagnosis of diseases is difficult,” she said. “It’s so much more difficult to try to figure out how people died hundreds of years ago.”
Infectious diseases are particularly difficult to identify, Professor Graham explained, as they usually don’t affect the skeleton.
“Almost no DNA could be detected on skeletons a while ago,” she said. “Detection methods have certainly improved.”
