DNA analysis identifies the horrible disease suspected of devastating Mexico after the arrival of the Spanish

The arrival of the conquistadors in Mexico around 1550 brought with it an epidemic so brutal that it killed 15 million Indians, 80% of the population of Mexico. For decades there has been speculation about the nature of that plague, and a new DNA analysis points to a surprising culprit: Salmonella.

Although characters of the time such as the Franciscan friar Fray Juan de Torquemada left evidence of the appalling symptoms of that epidemic, it is difficult to know for sure what was its scientific origin. Different hypotheses pointed to diseases such as mumps, smallpox, typhus or some type of hemorrhagic fever.

An exhaustive study carried out by researchers from the Department of Sciences and Human History of the Max Planck Institute, in Germany, has finally given us a tangible proof of the evil that devastated Mexico at that time. Researchers have extracted DNA samples from 30 skeletons found in the city of Teposcolula-Yucundaa, Oaxaca, and subjected them to a technique called the Meta Genome Analyzer Alignment Tool (MALT). The result? The people buried there died victims of Eberth's bacillus, a small bastard whose scientific name is Salmonella enterica of serotype Typhi.

The effects of this bacterium on the human being are much wilder than the severe gastroenteritis we know as Salmonellosis. The ancient Indians knew it by the name of cocoliztli (pestilence in the Nahuatl language). The Spaniards called it blood pumping. It is now known as typhoid fever, and if left untreated it is lethal in most cases.

Enteric bacterium Salmonella. Photo: Wikipedia
The contagion of typhoid fever was caused by drinking water or eating food contaminated with the bacteria by contact with a sick person. After about two weeks of incubation, the disease had high fever, vomiting, diarrhea, ulcers in the mucous membranes and inflammatory processes in various organs. If not treated properly, typhoid fever could degenerate into internal bleeding, intestinal perforation and septic shock. Nowadays it is a serious but treatable disease. At that time it was a death sentence except for a few who managed to survive the infection.

The discovery is interesting because it finally defines what exactly the Spaniards liberated in Mexico, but the technique used is even more important. MALT DNA analysis opens the door to studying the medical history of pests like this with an unprecedented level of accuracy. The investigation of remains through this technique will allow to shed light on other plagues and massive disappearances of ancient civilizations that even today are an enigma for science. [Nature Ecology & Evolution via Science Alert]