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New DNA technique suggests Salmonella took out the Aztecs

Research, published Monday in the journal Nature, reports DNA analysis has unmasked Salmonella enterica bacteria as the cause of a 16th century epidemic that affected large parts of Mexico and wiped out an estimated 800,000 people in the Aztec Empire.

The study, by Germany’s Max Plankc Institute for the Science of Human History, discovered the introduction of Salmonella in the Americas; which is believed to have been brought to the continent by Europeans. The identification of S. enterica bacteria, which causes typhoid, supports the theory that typhoid fever was the killer.

Before the researchers identified the pathogenic possibility, a 2000 study in the American Journal of Tropical Diseases concluded that the cause of the epidemic was some type of viral haemorrhagic fever. Prior to 2000, studies blamed measles and pneumonic plague. Salmonella was never considered a culprit.

Working with 24 corpses from a cemetery in the town of Teposcolula-Yucundaa, the Max Plankc researchers were able to extract biological material found between teeth. Based on historical and archaeological evidence, the cemetery was linked to the 1545–1550 epidemic, that was locally known as “cocoliztli,” the pathogenic cause of which has been debated for more than a century.”

Salmonella was a preveleant pathogen in Europe during the Middle Ages. Without prior exposure to Salmonella bacteria, indigenous populations of the Americas were 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,” the researchers concluded.

Pathogens that cause infectious diseases are a notorious challenge when it comes to identification in archaeological human remains for one big reason; they don’t leave skeletal traces. However, a new screening technique known as ‘MALT’ (Megan Alignment Tool) is proving promising for identifying the DNA of viruses and bacterial pathogens that caused ancient outbreaks.

The major advancement was an algorithm, offering a method of “analyzing many, many, many small DNA fragments that we get, and actually identifying, by species name, the bacteria that are represented,” according to the report.

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