Salmonella enterica genomes are recovered from the teeth of victims of a sixteenth century epidemic in Mexico in a paper published online this week in Nature Ecology & Evolution. The study represents the first known occurrence of salmonella in the Americas, which appears to have been introduced by Europeans to devastating effect.
Identification of infectious-disease-causing pathogens from archaeological human remains is notoriously difficult because most do not leave skeletal traces. Ashild Vagene and colleagues used a new screening technique called Megan Alignment Tool (MALT) to identify Salmonella DNA sequences from the teeth of ten indigenous individuals buried in a cocoliztli ('pestilence' in the indigenous Nahuatl language) cemetery, dating to the time of early European contact. Historical documentation of the cocoliztli epidemic symptoms had previously been used to argue that some form of typhoid or enteric fever was responsible for the outbreak. This identification of S. enterica (the bacterium that causes typhoid) supports typhoid as the culprit.
Without prior exposure to S. enterica, which is known to have been present in Europe in the Middle Ages, indigenous populations would have been highly vulnerable to infection, which could explain the high mortality rates of cocoliztli. This pattern is mirrored in the exchange of multiple diseases (such as smallpox, flu and measles) between Americans and Europeans in the centuries following first contact. As with typhoid, many of these diseases do not leave skeletal traces; however it is hoped the new MALT technique may in future be able to help identify the DNA viruses and bacterial pathogens that caused some of them.