What was Cocoliztli?

A team of German researchers from the Max Planck Institute for the Science of Human History and the Institute for Archaeological Sciences of Tubingen University could have identified the nature of the disease that decimated the Aztecs in the 16th century.

Estimated population graphic in Mexico between 1500 and 1840.

From 1545 to 1550 an unidentified disease wiped out the Aztecs. Native people name it Cocoliztli which translates as plague in the Nahuatl language. 15 millions died, i.e. around 80% of the population, which had been previously hit by smallpox. It was one of the deadliest epidemics of human history, after the great epidemic of Black Death (black plague) which spread over Western Europe in the 14th century. 30 years later, a second outbreak of cocoliztli killed half of the remaining population.

Until recently, the disease was supposed to be from European origin, but its real nature remained unknown. Measles, smallpox, mumps or even flu were considered. However, none of these diseases matches the symptoms described at the time: high fever, headache, nose, mouth and eyes bleeding.

By analyzing DNA, embedded in the teeth of individuals’ remains, buried in Teposcolula-Yucundaa, Åshild J. Vågene, Alexander Herbig and their team have identified a strain of salmonella enterica bacteria as the most likely cause of the epidemic, even if it can’t yet be excluded that multiple pathogen factors were involved in the cause of the epidemic. These bacteria cause enteric fever, identical to typhoid. While Europeans had been exposed to it for at least 300 years, the Aztecs had not developed immunity to it.

Sources: 1. Nature Ecology & Evolution, volume 2, pages 520–528, 2018 (paid access) - 2. National Geographic - 3. The Guardian, published in January 2018 and consulted in February 2018.