The story of the Aztecs is well known. After dominating much of Mesoamerica for three centuries, European diseases brought by Spanish invaders led by Hernán Cortés nearly wiped them out. The native word for these epidemics was cocoliztli (pestilence) and the worst occurred between 1545 and 1550 when 80 percent of the Aztecs died – upwards of 18 million people. That kind of “pestilence” can be caused by measles, smallpox or typhus and it has been assumed that one, if not all three, were responsible. But it’s never been proven by DNA analysis. That test has finally been run on human remains from this scourge and the surprise finding was not any of those but an early form of salmonella.
Researchers from the Max Planck Institute for the Science of Human History in Germany went to a burial ground in the Oaxacan highlands of southern Mexico and extracted DNA from the teeth of 24 people believed to have died during the cocoliztli. According to their report in the pre-print site bioRxiv, several of the teeth showed that they came from humans infected with Salmonella Paratyphi C, a severe form of Salmonella enterica which causes paratyphoid fever, a bacterial infection with the same symptoms and contagious effects as typhoid fever.
We propose that S. Paratyphi C contributed to the population decline during the 1545 cocoliztli outbreak in Mexico.
According to the report, “contributed to the population decline” means the disease was easily spread via the notorious fecal-matter-in-water-due-to-poor-sanitary-conditions method, killing 10-15 percent of those exposed to it. An account by a Franciscan historian describes the aftermath:
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.
For those who need more proof of where it came from, a separate study found evidence of Salmonella Paratyphi C in a young woman buried in Norway in the year 1200. Fortunately, this form of salmonella is extremely rare - but not extinct – today.
However, this new DNA evidence means it may have caused fatal epidemics in other areas that were once blamed on different bacterial or virus-caused diseases. It also reminds us how contagious and deadly the salmonella bacteria still is today.