When Spanish conquistadors arrived in what is now Mexico in 1519, the Aztec empire had about 25 million inhabitants.

Image attributed to Miguel Gonzalez of Hernan Cortes scuttling his fleet off the Veracruz coast. On display at the Naval History Museum in Mexico City. AlejandroLinaresGarcia

A century later, after a Spanish victory and a series of epidemics, the number of inhabitants was about one million.

“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,”

– A Franciscan historian who witnessed the 1576 outbreak.

The Aztecs fell victim to a host of different diseases brought by the Spaniards. But exactly which diseases have been unknown, until now.

New research from the German Max Planck Institute reveals that many Aztecs died of salmonella infection.

A team of researchers extracted and sequenced DNA from the teeth of 29 people buried in the Oaxacan highlands unearthed in southern Mexico.

They showed bacterial infection of the type Salmonella paratyphi C. A bacteria that cause enteric fever, a typhus-like illness, and that occurs mostly in developing countries today. It still kills about 10–15% of infected people if left untreated.

Åshild J. Vågene, Michael G. Campana et al. Salmonella enterica genomes recovered from victims of a major 16th century epidemic in Mexico doi: https://doi.org/10.1101/106740